[Federal Register: February 2, 2007 (Volume 72, Number 22)]
[Proposed Rules]               
[Page 4967-4997]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]



Fish and Wildlife Service

50 CFR Part 17

Endangered and Threatened Wildlife and Plants; 12-Month Finding 
on a Petition To List the American Eel as Threatened or Endangered

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Notice of 12-month petition finding.


SUMMARY: We, the U.S. Fish and Wildlife Service (USFWS), announce our 
12-month finding on a petition to list, under the Endangered Species 
Act of 1973, (Act) as amended, the American eel (Anguilla rostrata) as 
a threatened or endangered species throughout its range. After a 
thorough review of all available scientific and commercial information, 
we find that listing the American eel as either threatened or 
endangered is not warranted at this time. We ask the public to continue 
to submit to us any new information that becomes available concerning 
the status of or threats to the species. This information will help us 
to monitor and encourage the ongoing conservation of this species.

DATES: The finding in this document was made on February 2, 2007.

ADDRESSES: Data, information, comments, or questions regarding this 
finding should be sent by postal mail to Martin Miller, Chief, Division 
of Endangered Species, Region 5, U.S. Fish and Wildlife Service, 300 
Westgate Center Drive, Hadley, Massachusetts 01035-9589; by facsimile 
to 413-253-8428; or by electronic mail to AmericanEel@fws.gov.

FOR FURTHER INFORMATION CONTACT: Heather Bell, at the street address 
listed in ADDRESSES (telephone 413-253-8645; facsimile 413-253-8428). 
Persons who use a telecommunications device for the deaf (TDD) may call 
the Federal Information Relay Service (FIRS) at 800-877-8339, 24 hours 
a day, 7 days a week.

SUPPLEMENTARY INFORMATION: The complete administrative file for this 
finding is available for inspection, by appointment and during normal 
business hours, at the street address listed in ADDRESSES. The petition 
finding, the status review for American eel, related Federal Register 
notices, and other pertinent information, may be obtained online at 


    Section 4(b)(3)(B) of the Act, as amended (16 U.S.C. 1531 et seq.), 
requires that, for any petition to revise the Lists of Endangered and 
Threatened Wildlife and Plants that contains substantial scientific and 
commercial information that listing may be warranted, we conduct a 
status review and make a finding within 12 months of the date of 
receipt of the petition (hereafter referred to as a 12-month finding) 
on whether the petitioned action is (a) not warranted, (b) warranted, 
or (c) warranted but the immediate proposal of a regulation 
implementing the petitioned action is precluded by other pending 
proposals to determine whether any species is threatened or endangered, 
and expeditious progress is being made to add or remove qualified 
species from the Lists of Endangered and Threatened Wildlife and 
    On May 27, 2004, the Atlantic States Marine Fisheries Commission 
(ASMFC), concerned about extreme declines in the Saint Lawrence River/
Lake Ontario (SLR/LO) portion of the species' range, requested that the 
USFWS and the National Oceanic and Atmospheric Administration's 
National Marine Fisheries Service (NMFS) conduct a status review of the 

American eel. The ASMFC also requested an evaluation of the 
appropriateness of a Distinct Population Segment (DPS) listing under 
the Act for the SLR/LO and Lake Champlain/Richelieu River portion of 
the American eel population, as well as an evaluation of the entire 
Atlantic coast American eel population (see Finding for definition of 
DPS) (ASMFC 2004a, p. 1). The USFWS responded to this request on 
September 24, 2004; our response stated that we had conducted a 
preliminary review regarding the potential DPS as described by the 
ASMFC, and determined that the American eel was not likely to meet the 
discreteness element of the policy requirements due to lack of 
population subdivision (further analysis is provided under Finding). 
Rather, the USFWS agreed to conduct a rangewide status review of the 
American eel in coordination with NMFS and ASMFC (USFWS 2004, p. 1).
    On November 18, 2004, the USFWS and the NMFS received a petition, 
dated November 12, 2004, from Timothy A. Watts and Douglas H. Watts, 
requesting that the USFWS and NMFS list the American eel as an 
endangered species under the Act. The petitioners cited destruction and 
modification of habitat, overutilization, inadequacy of existing 
regulatory mechanisms, and other

[[Page 4968]]

natural and man-made factors (such as contaminants and hydroelectric 
turbines) as the threats to the species.
    On July 6, 2005, in response to the petition, the USFWS issued a 
90-day finding on the petition (70 FR 38849), which found that the 
petition presented substantial information indicating that listing the 
American eel may be warranted. The finding noted concern that the 
dramatic decrease in recruitment of American eel noted at the Moses-
Saunders Dam in Canada (on the St. Lawrence River), coupled with the 
significant decline seen in the European eel (ASMFC 2000, pp. 12-14), 
could indicate a decline in the American eel. Information on possible 
reasons for this suggested decline included the following threats: 
Commercial harvest, habitat loss and degradation (primarily the loss of 
wetlands and upper tributary habitat), hydropower turbine mortality, 
and inadequacy of existing regulatory mechanisms. Other potential 
threats, such as seaweed harvest, benthic (sea or lake bottom) habitat 
destruction, alterations of stream flow, disease, predation, and 
contaminants, were not fully addressed or supported by the information 
presented in the petition. Further analysis of oceanic variations (such 
as changes in the Gulf Stream) were recommended in the 90-day finding, 
particularly in light of the scant direct evidence and the potential 
for oceanic variations to be compounding or confounding the impact of 
other threats. Additionally, the 90-day finding concluded that the 
complex life history and the incompleteness of historical data 
(abundance, stock composition, life stage mortality rates, and 
exploitation rates) made it challenging to understand the potential 
influence of multiple threats to the American eel (USFWS 2005a, p. 
    In response to our 90-day finding's request for information for use 
in the species' status review, we received comments and information on 
American eel from the majority of the State fish and wildlife agencies 
within the range of the eel; State universities; State and university 
museums; the U.S. Forest Service (USFS); National Park Service (NPS); 
U.S. Geological Survey (USGS); Army Corp of Engineers (ACOE); the 
Department of Defense; the ASMFC; the Great Lakes Fisheries Commission; 
Department of Fisheries and Oceans (Canada); Tribal Nations; academics 
and researchers from the United States, Canada, Japan, and several 
European countries; hydropower and fishing industries; nongovernmental 
organizations; private citizens; and other entities. Additionally, we 
coordinated with the USFWS's International Affairs Program (IAP) to 
obtain information on international trade and with State and Federal 
law enforcement officials on illegal trade. Although all countries 
where the American eel is native were contacted regarding information, 
there was no available data on eel distribution, habitat use, habitat 
degradation or loss, or other threats (other than international harvest 
data) from Central or South America. Distribution information was 
provided by some Caribbean Islands. Therefore, the status review 
focused on where data is available within the North American Continent.
    A status review allows for additional collection, clarification, 
and interpretation of information on the status of the species by the 
USFWS. The resulting status review, from which the 12-month finding is 
based, relied on our extensive review of the existing literature, data 
resulting from the 90-day finding request for information, and new 
information obtained during the status review period. Among the new 
information we received, the documents most relevant to the status 
review include the recently completed stock assessments for the 
Atlantic coast (ASMFC 2006a and b), the American eel data assembled for 
the Canadian stock assessment (Cairns et al. 2005), and recently 
completed research on life history and potential threats to the 
American eel (van den Thillart et al. 2005; Oliviera in USFWS 2006; 
Machut 2006; Lamson et al. 2006; Devarut et al. 2006; Knights et al. 
    Also, because of the large body of literature and the uncertainty 
surrounding several threats, we hosted two scientific workshops with 
over 25 scientific experts. The goal of the workshops was to insure 
that the USFWS properly utilized the best and most current scientific 
and commercial data available in conducting the status review. To reach 
this goal, each of the experts was asked a series of facilitated 
questions to assess the presented information (which included multiple 
factual inputs, data, models, assumptions, etc.), including the 
completeness of the literature selected, and to comment on the 
relevance and quality of the literature for purposes of our status 
review (see workshop summaries Web site at http://www.fws.gov/northeast/ameel/
). The USFWS recorded each expert's individual 

assessments and the basis for those assessments in a compendium (cited 
in the finding as USFWS 2005b and 2006). Workshop objectives included 
determining the following: Utility of the information; life history 
stages vulnerable to certain threats; the geographic scope of the 
threats; the immediacy of the threats; and uncertainties in the 
available information and the potential implications of those 
uncertainties in making a status determination.
    The selection of the expert panelists was based on recommendations 
from within and outside of the USFWS and NMFS (the Services). The 
panelists selected represented a broad and diverse range of scientific 
perspectives relevant to the status review of the American eel coming 
from State and Federal agencies, fishery commissions, Tribes, academia, 
domestic and foreign research institutions (Canada, Japan, and 
England), industry organizations, and nongovernmental organizations. 
Participating individuals had expertise on threats or life history 
characteristics associated with threats to the American eel.
    Therefore, in addition to the published literature, our review 
considered: (1) Each expert panelist's characterization of the threat 
(the life stages acted upon by the threat, the severity of the threat, 
and the timing of the threat) based on their own and other published 
and unpublished research on the species; (2) the basis for each expert 
panelist's assessments of the literature in the context of a rangewide 
status review; and, (3) each expert panelist's assessments of the 
implications of the uncertainty in the information. This finding 
therefore builds on, clarifies, reinterprets, and, in some cases, 
supersedes information presented in the 90-day finding.
    In conducting our 12-month finding for American eel, we considered 
all scientific and commercial information on the status of American eel 
that we had in our files. Parallels in life history traits that are 
unknown for the American eel are drawn from other species of Anguilla.

Evolution and Population Structure

    The American eel is one of 15 ancient species (evolving circa 52 
million years ago) of the worldwide genus Anguilla, whose members spawn 
in ocean waters, migrate to coastal and inland continental waters to 
grow, and then return to ocean spawning areas to reproduce and die--a 
life history strategy known as catadromy (McCleave 2001a, p. 800; Avise 
2003, p. 31; Knights et al. 2006, pp. 2-3).
    The North Atlantic is home to two, closely related, recognized 
species of Anguilla--the American eel and the European eel (A. 
anguilla) (Avise 2003, p. 31). Genetic research indicates that the 
American eel lacks appreciable phylogeographic population structure,

[[Page 4969]]

meaning that American eels are one, well-mixed, single breeding 
population, termed panmixia or panmictic (Avise 2003, pp. 34-35). This 
likely occurs from a combination of the random distribution of the 
eel's larval stage when they reach continental waters and random mating 
among all adults throughout the species' range. This is in contrast to 
many anadromous species (which, even though they have an oceanic phase, 
return to their rivers of origin to spawn), where mating is within 
separate populations that are geographically or temporally isolated.
    This panmictic life history strategy maximizes adaptability to 
changing environments and is well suited to species that have 
unpredictable larval dispersal to many habitats (Stearns 1977 in 
Helfman et al. 1987, p. 52). Additionally, by not exhibiting geographic 
or habitat-specific adaptations, eels have the ability to rapidly 
colonize new habitats and to re-colonize disturbed ones over wide 
geographical ranges (McDowall 1996 in Knights et al. 2006, p. 7).

Life History

    In brief, the life history of the American eel begins in the 
Sargasso Sea, where eggs hatch into a larval stage known as 
``leptocephali.'' These leptocephali are transported by ocean currents 
to the Atlantic coasts of North America and upper portions of South 
America. They enter coastal waters, where they may stay, or they may 
move into estuarine waters or migrate up freshwater rivers, where they 
grow as juveniles and mature. Upon nearing sexual maturity, these eels 
begin migration toward the Sargasso Sea, completing sexual maturation 
en route. Spawning occurs in the Sargasso Sea. After spawning, the 
adults die; a species with this life history trait is known as a 
semelparous species. For a detailed description of the life cycle and 
other life history characteristics, see McCleave 2001a, Tesch 2003, and 
Cairns et al. 2005. Aspects of the species' life history most relevant 
to this finding are discussed in more detail below.

Egg and Larval Life History Stage

    The egg and larval stage of the American eel occur in the Atlantic 
Ocean, the Sargasso Sea, ocean currents, and Continental Shelf waters.
    Sargasso Sea. The Sargasso Sea is part of the North Atlantic Ocean, 
lying roughly between the West Indies and the Azores. The Sargasso Sea 
is part of the western half of a large clockwise gyre (circular pattern 
of ocean circulation). It is here that American eel eggs hatch into a 
larval stage known as ``leptocephali.'' The leptocephali are 
distributed in the upper 300 meters (m) of the ocean and are subject to 
transport from surface currents in the Sargasso Sea. These surface 
currents can be complex due to the fronts that form in the Subtropical 
Convergence Zone (where equatorial and temperate waters meet) primarily 
in the winter and spring, and the eddies that are likely present year 
    Ocean current transport. The Sargasso Sea includes a powerful 
western boundary current, the Florida Current and Gulf Stream, which 
flows to the north and northeast along the Atlantic coast of North 
America. The Florida Current is the southern half of this flow, from 
the Straits of Florida to Cape Hatteras (Schott et al. 1988 in Miller 
2005, p. 3). The Florida Current transports water from the Caribbean, 
Gulf of Mexico, and more distant regions through the Straits of 
Florida. It then combines with Gulf Stream recirculation water from the 
Sargasso Sea as it flows north of the Bahamas (Marchese 1999, pp. 29, 
549), and forms the Gulf Stream off Cape Hatteras, North Carolina. Once 
past Cape Hatteras, the Gulf Stream (which is at least 48 km or 30 
miles offshore but more typically 160 km or 100 miles or greater 
offshore) usually has pronounced meanders, which, if large enough, can 
get separated and cast off to the north into the continental slope 
water (a water mass found in the permanent thermocline between the Gulf 
Stream and the continental shelf north of Cape Hatteras (35 [deg]N)). 
The flow of the Gulf Stream continues to the northeast, mostly 
paralleling the Atlantic coast, towards Europe and becomes the North 
Atlantic Current (Miller 2005, pp. 3-4).
    The majority of the leptocephali enter the Florida Current just 
south of Cape Hatteras (just south of where the Florida Current enters 
the Gulf Stream) directly from the Sargasso Sea. The remainder may 
enter the Florida Current by a more southern route (e.g., transported 
on the Caribbean Current through the Yucatan Straights (Kleckner and 
McCleave 1985, p. 89), to the Gulf Loop Current and then to the Florida 
Current, which would be the route most likely taken for Gulf of Mexico 
recruitment) (Kleckner and McCleave 1982, p. 329-330; Miller 2005, p. 
    The distribution of American eel leptocephali in the Florida 
Current was first described by Kleckner and McCleave (1982, pp. 334-
337; 1985, pp. 73-77). Additionally, they found evidence of westward 
movement of leptocephali across the current toward the coastal waters. 
Because the distances of transport, to southern and northern points 
along the Atlantic coast, differ by thousands of kilometers, it has 
been suggested that the timing of metamorphosis from leptocephali to 
the next life history stage may determine where individuals arrive in 
Continental Shelf waters.
    Other than likely current transport, we know very little about the 
American eel leptocephali. Recent studies on other species have 
indicated that leptocephali may feed on marine snow or specific 
detrital particles, such as discarded larvacean (planktonic tunicates 
that secrete a gelatinous house) houses and zooplankton fecal pellets 
(Otake et al. 1993, pp. 28-32; Mochioka and Iwamizu 1996, p. 447).
    Continental shelf waters. The American eel undergoes metamorphosis 
twice. The first occurs when the leptocephali enter the Continental 
Shelf waters (the area of shallow seas just off the coast to the area 
of marked increase in slope to greater depths); the second is during 
sexual maturation. The leptocephalis' leaf-like, laterally compressed 
shape transforms during metamorphosis into a reduced, 
characteristically eel-like shape, as they become transparent ``glass'' 
eels. Leptocephali are unusual fish larvae that are filled with a 
transparent gelatinous energy storage material, and they can swim 
either forwards or backwards (Miller and Tsukamoto 2004 in Miller 2005, 
pp. 1-2); this may be an important aspect in detraining from (getting 
off of) the Gulf Stream. According to Miller (2005), this directional 
swimming appears to be the only way that leptocephali can cross and 
detrain from the Gulf Stream system and cross the Continental Shelf 
waters, due to the lack of any persistent oceanic transport mechanism 
that can account for the large-scale transport of millions of larvae 
across the current.

Juvenile Life History Stage

    Arrival in coastal waters. When juvenile eels arrive in coastal 
waters, they can arrive in great density and with considerable yearly 
variation (ICES 2001, p. 2). Arriving juvenile eels (unpigmented 
``glass eels'' and pigmented ``elvers'') have been collected and 
recorded for 10 years from two sites in North Carolina in the Beaufort 
estuary. Densities as high as 13.5-14.0 eels/100m\3\ and as low as 1.5 
eels/100m\3\ have been recorded (Powles and Warlen 2002, p. 301). In 
the East River, Canada, Jessop (2000, p. 520) had daily counts of 
30,000 elvers entering the mouth of the river. Between May and August 
200,000 elvers were recorded by trap method, and a population estimate 
of 960,000 elvers was conducted by mark-

[[Page 4970]]

recapture (Jessop 2000, pp. 518-520). Variation in recruitment between 
years can be quite significant. In the 9 years of records between the 
years 1982 to 1999, estimated recruitment to the Petite rivi[egrave]re 
del la Trinit[eacute] varied roughly four-fold, from a low of 14,014 to 
a high of 61,308 (ICES 2001, p. 36). Some arrivals remain in brackish 
(estuarine) or marine (salt) waters, others migrate up rivers to a 
variety of fresh water habitats, and still others, as they mature, will 
show inter-habitat movement patterns (Jessop et al. 2002, pp. 217-218; 
Morrison et al. 2003, pp. 90-92; Cairns 2006a, p. 2; Thibault et al. 
2005, p. 36; Lamson et al. 2006, p. 1567; Daverat et al. 2006, p. 2).
    Juvenile mortality. Information on mortality rates for all of the 
life stages is limited. In Jessop (2000, p. 514), the recruitment of 
elvers to the East River, Chester, Nova Scotia, during May through July 
was estimated by mark-recapture population estimates to be 960,000 
elvers. The population size following migration to recapture sites 
about 1.3 kilometers (km) upstream during late July-October was 2,894 
elvers. These data indicate high juvenile mortality rates, in this case 
at a rate of 99 percent. This high mortality was attributed to the 
effects of low pH (4.7-5.0), high initial elver density (4.7 elvers/
m\2\) (which may lead to predation, including cannibalism, starvation, 
and competition for space), and predation by resident, presumably 
older, eels. V[oslash]llestad and Jonsson's (1988 in Jessop 2000, p. 
523) research indicates that eel mortality in fresh waters is density-
dependent when elver numbers exceed a certain abundance. Although it is 
not certain if early juvenile mortality is this high throughout the 
range of the species, this supports the observation, according to 
Jessop, that oceanic conditions may deliver relatively high quantities 
of elvers to rivers, such as those along the south shore of Nova Scotia 
(Jessop 1998 in Jessop 2000, p. 523), even to the point that elver 
abundances too great for habitat capacity can occur (Jessop 2000, p. 
523). Surviving juvenile eels mature into fully pigmented ``yellow 
    Mortality rates likely decrease with size. One study in Prince 
Edward Island, Canada, calculated loss from the population due to 
mortality and emigration. Estimates of loss in American yellow eels 
from the Prince Edward Island study are reported at 22 percent, with 
mortality rates decreasing to 12 to 15 percent as the juvenile yellow 
eels age (Anonymous 2001 in Morrison and Secor 2003, p. 1498), likely 
due to lower mortality from predation and starvation as size increases.
    Juvenile diet. The enormous dietary breadth of eels reflects their 
great adaptability with respect to nearly all conditions of water 
bodies. Yellow eels are opportunistic, consuming nearly any live prey 
that can be captured. Smaller eels eat benthic invertebrates; larger 
eels include mussels, fish, and even other eels in their diet. Yellow 
eels also adapt to seasonal changes, decreasing intake or ceasing to 
eat during the winter. Eels can also respond to local abundances of 
appropriately sized prey through the seasons (Tesch 2003, pp. 152-163). 
This adaptable diet allows for resource partitioning as well as the 
ability to withstand changes in local environmental conditions and the 
ability to occupy a geographically wide variety of habitats.
    Density-dependent dispersion. As young eels begin to grow, density-
dependent competition promotes eels to disperse into less crowded areas 
(Feunteun et al. 2003, pp. 201-204; Ibbotson et al. 2002 in Knights et 
al. 2006, p. 10). Aggressive interactions at high density inhibit 
feeding and growth, but stimulate dispersive swimming activity in 
smaller eels (Knights 1987 in Knights et al. 2006, p. 10), the latter 
likely as a defense against predation. As size differences in these 
juveniles increase, cannibalism can also be an important cause of 
mortality (Knights 1987 in Knights et al. 2006, p. 10). Density 
dependent dispersion ensures wider distributions, further minimizing 
intra-specific competition. Benefits of density dependent dispersion 
include selection of optimal habitat productivity and temperature, 
lower predation risks, rapid colonization or re-colonization of 
habitats, and avoidance of inter-specific competition. Larger 
individuals farther upstream tend to become more sedentary and occupy 
territories, densities of eels decline, and females predominate 
(Feunteun et al. 2003, p. 201).
    Distribution clines. It has been suggested that there are 
latitudinal clines in eel distribution related to river typologies. For 
example, the American eel tends to extend farther inland in southerly 
lowland drainages compared to distributions in the shorter and steeper 
post-glacial stream systems in the Northeast (Jessop et al. 2004 in 
Knights et al. 2006, p. 11). Smogor et al. (1995, p. 799) and Knights 
(2001 in Knights et al. 2006, p. 8) have documented decreases in 
densities with increasing distance from the Continental Shelf in a 
predictable pattern, likely as a result of density dependant dispersion 
and mortality due to predation. Although mean watershed densities 
decrease by an order of magnitude with distance inland from the 
Continental Shelf, mean biomass only declines by about 50 percent 
because mean body weight and eel length increase (and hence relative 
fecundity). This, according to Knights et al. (2006, p. 10), helps 
maintain biomass relative to carrying capacity. Machut (2006, p. 13) 
indicates that as barrier intensity increases, so does eel growth above 
the barrier. Recent research (Knights et al. 2006, pp. 11-13) has 
documented that as eel density decreases, the proportion of females 
increases, which, assuming females are the limiting sex, would be, 
according to Knights et al. (2006, p. 13), a compensatory mechanism 
during times or in areas of low density.

Sexually Maturing Life History Stage

    Sex determination. There are no morphologically differentiated sex 
chromosomes in the American eel (McCleave 2001a, p. 803). Prior to 
sexual differentiation, eels are intersexual, meaning they can develop 
into either sex. It is only when yellow eels reach a length of about 
20-35 cm that it is possible to distinguish males from females 
visually, and there is considerable variation in age and size at 
differentiation. The determination of sex is likely influenced by 
environmental factors, including eel densities (Tesch 2003, pp. 43-46). 
Studies indicate that as the density of eels in a particular area 
increases the number of male eels increases; decreasing density favors 
more females. It has been argued by Knights et al. (2006, p. 13), that 
an advantage of this life history strategy is that when recruitment 
declines, so will density and tendencies to migrate far upstream in 
rivers. In turn, this will lead to relative increases in the number of 
(larger) females and hence compensatory increases in fecundity. This 
may take a number of generations (and hence decades) to manifest 
itself, but this strategy confers enormous benefits in the face of 
threats, past, present and future, such as tectonic events and changes 
in ocean currents and climate (Knights et al. 2006, p. 13).
    Silvering. After a number of years, the yellow eels begin 
metamorphosis. Beginning at 3 years old and up to 24 years, with the 
mean becoming greater with increasing latitude (e.g., 6-16 years in the 
Chesapeake Bay region; Helfman et al. 1987, pp. 44-45; and 8-23 years 
in Canada; Cairns et al. 2005, p. 11), yellow eels metamorphose into 
``silver eels'' (Cairns et al. 2005, p. 13). This metamorphosis from 
bottom-oriented yellow eels to silver eels (termed ``silvering'') is a 
key physiological event

[[Page 4971]]

preparing these future spawners for oceanic migration and reproduction 
(van den Thillart et al. 2005, p. 12).
    Environmental factors may play a role in the triggering of 
silvering. Habitat conditions, such as food availability and 
temperature, will influence the size and age of silvering eels via 
growth conditions. Thus, variation in length and age at maturity can 
occur in different habitats (e.g., freshwater habitat versus estuarine 
habitat) within a restricted geographic range and over larger 
geographic scales as well.
    The length of the growing season and the temperature are negatively 
correlated with latitude, so age at maturity is strongly correlated 
with latitude (McCleave 2001a, p. 803). Characteristics of silver eels 
vary across the species' range. Eels from northern areas, where 
migration distances are great, show slower growth and greater length, 
weight, and age at migration, preparing them, it could be assumed, for 
the longer migration.
    Indeed, favorable growth conditions cause eels to silver more 
rapidly (V[oslash]llestad and Jonsson1988 in Jessop 2000, p. 522; 
V[oslash]llestad 1988 and 1992 in van den Thillart 2005, p. 56; De Leo 
and Gatto 1995 in van den Thillart 2005, p. 56) such as is the case in 
aquaculture, under experimental conditions (Tesch 1991 and Beullens et 
al. 1997 in van den Thillart et al. 2005, p. 56), or in brackish water 
and at low latitudes (Lee 1979 and Fernandez-Delgado et al. 1989 in van 
den Thillart et al. 2005, p. 56). For example, Morrison et al. (2003, 
p. 95-96) found annual growth rates in brackish water were two times 
higher than growth rates of eels that resided entirely in fresh water. 
Also American eels in U.S. southern Atlantic coast waters develop into 
silver eels about 5 years sooner than northern populations (Hansen and 
Eversole 1984, p. 4; Helfman et al. 1984, p. 139), likely as a result 
of warmer, more stable water conditions (Helfman et al. 1984, p. 138).
    Variation in maturation age benefits the population by allowing 
different individuals of a given year class to reproduce over a period 
of many years, which increases the changes of encountering 
environmental conditions favorable to spawning success and offspring 
survival. For example, variability in the maturation age of eels born 
in 2006 may result in spawners throughout 2010-2030, during which time 
favorable environmental conditions are likely to be encountered at 
least once.
    Additionally, males and females differ in the size at which they 
begin to silver. Eels appear to need to reach a certain size to begin 
the silvering process, with this size increasing with age (thus, 
rapidly growing eels will silver at smaller sizes than slow-growing 
eels). In males, silvering happens at a very early stage, at a size 
typically greater than 35 centimeters (cm). In females, silvering 
happens at a size greater than 40 to 50 cm (Goodwin and Angermeier 
2003, p. 530; van den Thillart et al. 2005, pp. 31, 55).
    Actual metamorphosis is a gradual process occurring during the 
summer, and in the fall eels metamorphosing in preparation for 
migration back to the spawning grounds have a silvery body color, 
enlarged eyes and nostrils, and a more visible lateral line (Dave et 
al. 1974; Lewander et al. 1974; Pankhurst 1983; and Barni et al. 1985 
in van den Thillart 2005, p. 12). As the structure and metabolism of 
the liver changes, the swim-bladder also changes, allowing for 
increased gas deposition rates and decreased loss of gas (McCleave 
2001a, p. 804).
    A drop in temperature appears to trigger the final events of 
metamorphosis (gut regression and cessation of feeding), which will 
lead to migratory movements under the appropriate environmental 
conditions. It is theorized that responding to a drop in temperature 
would help to synchronize out-migrating eels, thus increasing their 
chances of reaching the Sargasso Sea simultaneously. Conversely, 
increasing temperatures, delays in migration, or possibly low fat 
content will cause eels to start feeding again and to revert to a 
yellow resident stage. This would happen in the natural environment if 
eels did not reach the sea before the end of the migrating season. It 
has been observed that even after eggs and sperm have developed, eels 
are capable of gut regeneration and feeding (Fontaine et al. 1982, 
Dollerup and Graver 1985, in van den Thillart et al. 2005, p. 56). Van 
den Thillart et al. (2005, p. 56) confirmed that silvering may occur 
more than once in the lifetime of an eel. It has been said that this 
phenomenon would explain the extreme variability in age and size of 
silver eels. It has been hypothesized that conditions encountered 
during oceanic migration, such as the high pressure they would 
experience at depth in the open ocean, may complete the sexual 
maturation of eels (Fontaine et al. 1985 in van den Thillart et al. 
2005, p. 13).

Outmigration Life History Stage

    Energy requirements. To successfully complete the migration from 
the continent to the Sargasso Sea (out-migration), great endurance and 
an extensive fat reserve are required. Larger, fatter eels have an 
advantage over smaller eels in reaching the Sargasso Sea and having 
sufficient energy stores to reproduce. Eels are very efficient swimmers 
(eels swim approximately four to six times more efficiently than 
salmonids), and larger eels appear more efficient than smaller eels 
(van den Thillart et al. 2005, pp. 106-107). Also, larger eels usually 
have larger fat stores per body weight. Silver eels have ceased 
feeding, and use their stored fat for energy during their migration and 
for completing gonadal growth. In a study conducted on European eel, 
the most recent estimate of necessary energy (fat) needed to 
successfully complete the migration to the Sargasso Sea from Europe and 
spawn is 20 percent fat reserves, of which 13 percent is for transport, 
and an additional 7 percent for completing gonadal growth. In European 
silver eel, about 50 percent of the eels studied had a fat percentage 
of 20 percent (van den Thillart et al. 2004 in van den Thillart et al. 
2005, p. 109).
    It is unknown if American eels require 20 percent fat reserves. 
American eels travel a shorter distance to reach the Sargasso Sea than 
do European eels. Actual distances, routes, and depths of migration for 
adult eels are unknown. Distances traveled by migrating silver American 
eels likely vary from under 1,500 km to over 4,500 km, shorter than the 
5,000 km to 7,000 km likely traveled by European eels. An American eel 
maturing in the Mississippi River, Louisiana, would travel a distance 
of over 2,200 km; from South Carolina, 1,440 km; from Chesapeake Bay, 
Virginia, 1,550 km; from Newfoundland, Canada, over 2,800 km (McCleave 
2001a, p. 805); and from western Lake Ontario, over 4,500 km. Silver 
eels, it has been hypothesized by Knights (2003, p. 240), may follow 
the deep currents (for American eel, the Deep Western Boundary Current) 
to return to the Sargasso Sea. However, others believe the American eel 
migrates in the upper portions of the ocean (see van Ginneken and Maes 
2005, pp. 385-387; Tesch 2003, pp. 206-207).
    Fecundity. Fecundity also varies with size. Fecundity increases 
exponentially with length, ranging from about 0.6 million to almost 30 
million eggs depending on the size of the female (McCleave 2001a, p. 
804). As an example, in the lower Potomac watershed, the average silver 
female length of 734 mm would produce 2.7 million eggs; farther up the 
watershed the average silver female length of 870 mm would produce 5.2 
million eggs (Goodwin and Angermeier 2003, p. 533). Fecundity is also 
linked to the habitat which the eel occupies. In an eel

[[Page 4972]]

farm growth experiment, favorable nutrition was one of two factors (the 
other being genetic heterozygosity, where 2 different alleles are at 
one loci) producing eels with a high reproductive capacity (van den 
Thillart et al. 2005, p. 232). This high fecundity is thought to 
compensate for very high larval mortality (reported by Knights et al. 
2006, p. 4, as most probably well in excess of 99 percent).
    Spawning. Spawning takes place in the Sargasso Sea (Schmidt 1922 in 
Bo[euml]tius and Harding 1985, p. 122). Here, in the area where 
northern and southern waters meet, it has been hypothesized that there 
is some unidentified feature of the surface water (perhaps the abrupt 
horizontal temperate change of the frontal zone located within the 
subtropical convergence) that serves as a cue for migrating adults to 
cease migration and begin spawning (Kleckner et al. 1983, p. 289; 
Kleckner and McCleave 1988, pp. 647-648; Tesch and Wegner 1991 in 
Miller 2005, p. 1). Spawning has not been witnessed by humans, but the 
assumption is that adult eels die after spawning.


    The extensive range of the American eel includes all accessible 
river systems and coastal areas having access to the western North 
Atlantic Ocean and to which oceanic currents would provide transport. 
These drainages and coastal areas are along more than 50 degrees of 
latitude (from 5[deg] to 63[deg]) of the western North Atlantic Ocean 
coastline, from Northern Brazil/Venezuela to southern Greenland (Scott 
and Crossman 1973, pp. 624-625; Tesch 2003, pp. 92-97; Helfman et al. 
1987, p. 42), including most Caribbean Islands and Bermuda, the eastern 
Gulf of Mexico and associated drainages including the extensive 
Mississippi River watershed (e.g., Mississippi River, Ohio River, 
Tennessee River, Arkansas River, and Missouri River) as far north as 
Minnesota, the Gulf of St. Lawrence and the associated rivers, and Lake 
Ontario and associated drainages. It is believed that the eel was 
absent from the waters of Lakes Erie, Huron, and Superior before the 
completion of the Welland Canal in 1829 (Patch 2006, p. 2). In 1878, 
the Michigan Fish Commission planted young eels in southern Michigan 
waters, and for more than a decade, beginning in 1882, the Ohio Fish 
Commission released young eels throughout Ohio, including drainages to 
Lake Erie (Trautman 1981, pp. 192-193) (Figure 1). This extensive range 
should provide the American eel with a buffer against adverse 
conditions, as spawners would still be coming from areas not 
experiencing adverse conditions, and would, due to random dispersal and 
relatively homogeneous genetic structure, be capable to successfully 
re-colonize areas once the threat has abated.

[[Page 4973]]



[[Page 4974]]

    It has been reported in other documents that Bo[euml]tius and 
Harding (1985) estimated that the American eel range covers more than 
10,000 km of coastline; however, we could not locate this information. 
Utilizing current mapping technology, our estimate of the available 
coastline (including barrier islands) from Maine to Texas (Atlantic and 
Gulf coast) is 29,612 km (Castiglione 2006, p. 1).
    As a result of oceanic currents, the majority of the American eel 
population is located along the Atlantic seaboard of the United States 
and Canada. The historic and current distribution of the American eel 
within its extensive continental range is well documented along the 
United States and Canadian Atlantic coast, and the SLR/LO. The 
distribution is less well documented and likely rarer, again due to 
currents, in the Gulf of Mexico, Mississippi watershed, and Caribbean 
Islands, and least understood in Central and South America.


    The American eel is said to have the broadest diversity of habitats 
of any fish species (Helfman et al. 1987, p. 42) by occupying multiple 
aquatic habitats. From an evolutionary standpoint, this generalist use 
of habitats is favored in fluctuating environments, while specialists 
excel under constant or slowly changing environmental conditions 
(Richmond et al. 2005, pp. 279-280).
    During their spawning and oceanic migrations, eels occupy 
saltwater, and in their continental phase, they use all salinity zones: 
Fresh, brackish, and marine (for detailed habitat use by life stage, 
see Cairns et al. 2005). Eels occur in waters highly productive to fish 
species and those that are not, and from waters of near tropical 
temperatures to waters that are seasonally ice-covered (McCleave 2001a, 
p. 800).
    Growing eels are primarily benthic, utilizing substrate (rock, 
sand, mud) and bottom debris such as snags and submerged vegetation for 
protection and cover (Scott and Crossman 1973, p. 627; Tesch 2003, pp. 
181-183). In Canadian waters, American eels hibernate in mud during the 
winter. Wintering areas include fresh water, brackish estuaries, and 
bays with full strength salt water (Cairns et al. 2005, p. 3.4.6).
    Barring impassable natural or human-made barriers, eels occupy all 
freshwater systems, including large rivers and their tributaries, 
lakes, reservoirs, canals, farm ponds, and even subterranean springs. 
The anquillid (eel-shaped) body form allows for climbing when at young 
stages and under certain conditions (e.g., rough surfaces), allowing it 
to pass up and over some barriers encountered during upstream 
migrations in freshwater streams (Craig 2006, pp. 1-4). Eels are able 
to survive out of water for an exceptionally long time (eels can meet 
virtually all their oxygen needs through their skin), as long as they 
are protected from drying (for which their ability to produce mucus is 
of great adaptive significance), and eels have been seen using overland 
routes (while moist) when they encounter a barrier, explaining their 
entrance into landlocked waters (Tesch 2003, pp. 184-185) and their 
presence above numerous dams and weirs (USFWS 2005b, pp. 16-18).
    Abundance. Abundance (density) and distribution of eels within 
habitats may be a function of distance from the ocean and may not be 
related to habitat features (Smogor et al. 1995, pp. 796-797) (see also 
Density-Dependant Dispersion). According to Smogor et al. (1995, p. 
799) when examining Virginia streams, they found little connection 
between habitat features and the distribution and abundance of American 
eels at least at a large scale. Their results, they suggest, 
demonstrate a diffusion pattern of eel occurrence. This lack of eel-
habitat relations (at least at a large scale) within freshwater systems 
suggests that comparison of abundance for purposes of identifying 
quality habitat would be misleading. Rather, it has been suggested 
(USFWS 2006, pp. 13-14, 22) that the reproductive contribution of an 
area to the total American eel population would be the best manner of 
identifying quality habitat; however, reproductive contribution 
estimates from throughout the range of the American eel are not 
available. Examples of densities provided below are to illustrate the 
variation of densities, not for comparison of habitat importance. 
Machut (2006) summarized freshwater and brackish water density research 
and standardized to eel densities per 100m\2\. In Lake Champlain, 
Vermont, densities ranged from 2.32-6.36 eel/100m\2\ (LeBar and Facey 
1983 in Machut 2006, p. 50). In a tidal creek, Georgia, densities 
ranged from 1.82-2.32 eel/100m\2\ (Bozeman et al. 1985 in Machut 2006, 
p. 50). A Massachusetts salt marsh yielded densities of 8.46-9.28/
100m\2\ (Ford and Mercer 1986 in Machut 2006, p. 50). In Machut's own 
study in the Hudson River freshwater tributaries densities ranged from 
0.28-155.06/100m\2\ (Machut 2006, p. 50), while in brackish waters 
Morrison and Secor (2003 in Machut 2006, p. 50) reported densities of 
0.03-0.24/100m\2\ . In four Maine freshwater rivers, densities ranged 
from 1.80-35.40/100m\2\ (Oliveira and McCleave 2000, p. 144). Recent 
population estimates of juvenile eels (mostly elvers) on the South Anna 
River in Virginia were 1.88 eels/100m\2\. On the North Anna River, 
where the eels were smaller, the population estimate was greater at 
4.48/100m\2\ (Odenkirk 2006, p. 1). No estimates of abundance or 
density are yet available for marine waters.
    Habitat associations at a finer scale, such as areas within a lake, 
have recently been researched by Cudney (2004). In her studies, she was 
able to associate certain short-term habitat conditions, such as non-
stagnant waters and to a lesser extent long-term habitat features such 
as water depth and percent organic matter, to a higher probability of 
eel capture (Cudney 2004, pp. 57-60).
    Facultative Catadromy. Contrary to the earlier dominating paradigm 
that the eel growth phase is restricted to fresh water, it has been 
suggested that brackish (or estuarine) waters produce eels that grow 
faster, mature earlier, and emigrate as silver eels sooner than eels in 
fresh water, and that some eels complete their life cycle in brackish 
or marine waters without ever entering fresh water. Facultative 
catadromy, therefore, refers to migrations into fresh water as not 
being obligatory (Tsukamoto and Arai 2001, p. 2651).
    Morrison et al. (2003, p. 94) found annual growth rates in brackish 
water were two times higher than growth rates of eels that resided 
entirely in fresh water. The mechanism for this higher growth in 
brackish water is not well understood. Possible causes include an 
increase in quality or quantity of food, increase in habitat quality 
(Helfman et al. 1987 in Morrison et al. 2003, p. 94), lower resting 
metabolism resulting from living in near-isoosmotic (same salinity 
within the eel as the external environment) conditions, increased water 
temperature (which reduces the amount of time that eels are dormant 
during winter) (Walsh et al. 1983 in Morrison and Secor 2003, p. 1499), 
reduced effects from parasites, decreased predation, or decreased 
intra- or inter-specific competition. Morrison and Secor (2003, p. 
1499) hypothesized that the higher brackish-water eel growth measured 
on the Hudson River is general to most large North American estuaries.
    Two other studies became available during our status review, which 
provided data on use by eels of marine habitats during the eel growth 
phase (Daverat et al. 2006; Lamson et al. 2006). The first study, by 
Daverat et al. 2006,

[[Page 4975]]

looked at habitat plasticity in the American, European, and Japanese 
eel (A. japonica;) the second, by Lamson et al. (2006), at American eel 
in Canadian waters. In the first study, habitat use consisted of either 
residency in one habitat (fresh, brackish, or marine) or movements 
between habitats. Seasonal or minor (1 or 2) movement patterns were 
seen from brackish water to fresh water and vice versa. Single habitat 
switch events occurred, usually between 3 and 5 years of age. 
``Nomadic'' movement between water masses of different salinity was 
common; the differences in productivity between freshwater and brackish 
habitats (and the resulting lower growth of eels in temperate 
freshwater sites), the authors state, might explain this phenomenon. 
Occurrence of eels with no freshwater experience was demonstrated, but 
such eels accounted for a smaller proportion of the overall sample than 
did eels with some (even brief) freshwater experience. Another 
interesting result was that eels tend to prefer brackish and marine 
habitats for feeding at the northern extremes of their range. The 
authors also suggest that this high degree of habitat use plasticity 
suggests a remarkable ``bet hedging'' strategy for angullids as a group 
(Daverat et al. 2006, p. 11). In the second study, conducted on 
American eels in Canada, marine (saltwater) resident eels were the 
dominant migratory contingent of eels in saltwater bays (85 percent). 
Resident eels were established in salt and freshwater habitats by the 
year after their arrival in continental waters. Eels that shifted 
between habitats increased their rate of inter-habitat shifting with 
age. This study also showed that plasticity of habitat usage is the 
norm among eels, and that the American eel life cycle can be completed 
in marine waters (Lamson et al. 2006, p. 1572). A study of Japanese eel 
found that estuarine (43 percent) and marine (40 percent) eels 
contributed more spawners than did eels from freshwater areas (17 
percent), with some seasonal differences. Additionally, the study noted 
that eels from all three habitats began their marine spawning migration 
at about the same time. The implication here is that eels from all 
habitats can mix together during spawning migration and potentially 
contribute to the next generation (Kotake et al. 2005, p. 220). In 
Tsukamoto et al's evolutionary perspective, the authors hypothesize, 
based on Inoue 2001, that molecular evidence might suggest that 
catadromous Anguillidae come from deep-sea eels, with a migration loop 
that extended to coastal waters and incidentally visited estuaries; 
these eels may have eventually obtained a reproductive advantage 
because of higher food availability in estuaries than in freshwater 
(Tsukamoto et al. 2002 in Miller 2005, p. 2).
    According to Lamson et al. (2006, p. 1568), [Eacute]deline and 
[Eacute]lie (2004) reported that European glass eels have distinct 
individual salinity preferences. This implies that young eels separate 
into migratory contingents upon arrival on the coast, with salt-seeking 
eels remaining in marine waters while fresh-seekers ascend into fresh 
    The benefits of facultative catadromy include resource 
partitioning, by minimizing intra-specific competition between life 
stages and cannibalism of young by adults. Additionally, there are 
growth-temperature benefits, as shallow brackish and fresh waters 
(especially still waters) will heat up faster in the spring and summer 
than marine waters. Although not tested by any large-scale quantitative 
distribution data, the effective reproductive contribution of brackish/
marine habitats may be substantial (Tsukamoto and Arai 2001, p. 275; 
Jessop 2002, p. 228; Kotake et al. 2005, p. 220; Knights et al. 2006, 
pp. 12-13; Cairns 2006a, p. 1). Densities may be relatively low in 
coastal waters, but for European eel in England and Wales, Knights et 
al. (2001 in Knights et al. 2006, p. 13) calculated that estuarine and 
shallow coastal waters (estimated at 5,000 km\2\) exceed that of 
freshwater (1,035 km\2\).
    Clinal Variations. American eels show clinal variation (gradual 
changes over a geographic area) in their growth rates and size at 
maturity between the southern and northern portions of their range. 
Although mostly a warm water species, Anguillids are eurythermal 
(tolerant of a wide range of temperatures) and can survive extremes by 
migratory and cryptic behaviors. Even so, growth seasons inevitably 
shorten with increasing latitude. This produces clines as you move 
north of slower growth rates and larger size at maturity, thus 
retaining relative fecundity with increasing latitude (Knights et al. 
2006, p. 6).

Population Status

    Typically an evaluation of population status for a 12-month finding 
would include a rangewide estimate of population size and information 
on the demographic structure of the population and subpopulations as 
well as population trend information in context with historical data, 
and possibly an evaluation of the long-term viability of the current 
population through a population viability analysis model.
    No rangewide estimate of abundance exists for the American eel. 
Information on demographic structure is lacking and difficult to 
determine because the American eel is a single population (panmixia) 
with individuals randomly spread over an extremely large and diverse 
geographic range, with growth rates and sex ratios environmentally 
dependent. Because of this unique life history, site-specific 
information on eels must be evaluated in context with its significance 
to the entire population. Determining population trends is challenging 
because the relevant available data is limited to a few locations that 
may or may not be representative of the species' range and little 
information exists about key factors such as mortality and recruitment 
which could be used to develop an assessment model. Furthermore, the 
ability to make inferences about species' viability based on available 
trend information is hampered without an overall estimate of eel 
abundance. Despite these challenges we have determined the species 
currently appears stable, as we explain below.
    The Stock Assessment Committee of the ASMFC recently assessed the 
``stock status'' of the American eel (ASMFC 2006a), and this assessment 
was subsequently reviewed by an independent panel of scientists (ASMFC 
2006b). The Stock Assessment Committee concluded that the status of the 
stock is uncertain as a result of insufficient data. Their conclusion 
was based on the review of nine indices, two were fisheries-dependent 
and seven were fisheries-independent. Of these indices, one index shows 
an upward trend over time, one shows no trend, and the remaining seven 
show a downward trend (ASMFC 2006a, p. x). The committee hypothesized 
that the indices exhibiting a downward trend suggest that the stock is 
at or near documented low levels. The glass eel data from two Atlantic 
Coast sites were not used, and the panelists who reviewed the stock 
status felt that these indices were a valuable asset. These panelists 
interpreted the absence of a declining trend in glass eel abundance in 
either series over the last 14 to 15 years as the only positive 
indicator that recruitment, at least to the glass eel stage to these 
portions of the coast, had not declined in concert with some of the 
yellow eel indices (ASMFC 2006b, p. 4). The ASMFC stock status 
assessment has limited value in the 12-month finding because the 
purpose of the ASMFC stock status assessment is to inform management of 
the commercial

[[Page 4976]]

American eel fishery by determining allowable harvest, not to look 
specifically at long-term viability of the species.
    Recently Canada completed its review of the American eel status 
within Canadian waters as part of the Committee on the Status of 
Endangered Wildlife in Canada's (COSEWIC) review for possible listing 
under their version of the Endangered Species Act, known as Species At 
Risk Act (SARA). This review also was more similar to a stock status 
assessment than a population viability analysis. They determined that 
indicators of the status of the total Canadian component of this 
species were not available. Their evaluation of the data (indices of 
abundance in the upper SLR/LO declined by approximately 99 percent 
since the 1970s and four out of five time series from the lower St. 
Lawrence River and Gulf of St. Lawrence declined) led them to apply the 
Special Concern designation (COSEWIC 2006, p. III). Because the COSEWIC 
review focuses on the status of American eels in Canadian waters, the 
report also discussed the ``rescue effect.'' In the hypothetical 
scenario where the American eel became depleted or extirpated within 
Canadian waters external components would ``rescue'' the species in 
Canada. These external components refer to the young eels from the 
Sargasso Sea that are from American eels whose parents originated from 
U.S. waters, and experience random dispersal due to oceanic currents 
which would continue to deposit leptocephali into Canadian waters 
(COSEWIC 2006, p. 43).
    Together, however, these reports provide a more recent presentation 
of the individual data sets than was available in the stock status 
report by the International Council for the Exploration of the Sea or 
ICES (2001, pp. 51-52), which was the only stock assessment available 
at the time of the 90-day finding published on July 6, 2005 (70 FR 
38849). As a result of these factors, our assessment of the American 
eel population status will utilize the available information to: (1) 
Provide context of historical reports and current landings data as a 
surrogate for absolute abundance estimates; (2) evaluate the data from 
each different life stage and the significance of that life stage when 
evaluating the population status of the species including trend data in 
specific geographic areas and each area's significance to the 
population status of the species; and (3) evaluate the data to 
determine if there is a sustained downward trend in a location or 
locations that would be considered representative of the entire range. 
Together these will provide the basis for our assessment of whether the 
species is currently being impacted by threats to the degree that the 
American eel meets the definition of threatened or endangered. In 
addition, in the 12-month finding we also take into account the 
species' life history characteristics and compensatory mechanisms (see 
Background and for further discussion).

(1) Historical and Current Information

    Historically eels were a significant winter food source for Native 
Americans (see Casselman 2003, for a compilation of prehistoric and 
historic information from the United States and Canada) and later for 
European settlers. However, qualitative rather than quantitative 
information is all that is available from these early times. In the 
early 1900s, records from commercial fisheries began to appear. For 
example, weirs at Oneida Lake, Canada, caught 100 metric tons (220,000 
pounds) annually of emigrating eels (Adams and Hankinson 1928 in 
Casselman 2003, p. 260). Casselman cites the subsequent construction of 
dams and canals, which restricted access to the lake as the reason for 
its eventual extirpation from Lake Oneida. Given the size of the 
harvest, Casselman concludes that recruitment immigration in the past 
was much more extensive and probably much greater than in recent times.
    Although the current status of American eels cannot be described in 
absolute terms because rangewide estimates of abundance do not exist 
(ASMFC 2006a, p. viii; ASMFC 2006b, pp. 3, 13), we provide below recent 
ASMFC and COSEWIC landings data (long-term fishery independent indices 
do not exist) that indicate that the order of magnitude of yellow and 
silver phase eel abundance is probably in the many millions. In the 
past decade, commercial fisheries in the United States and Canada have 
landed approximately 800 metric tons (1.8 million pounds) of yellow and 
silver phase American eels annually (ASMFC 2006a, p. 82). These 
landings data provide a general sense of eel abundance if we make 
assumptions about the size and relative proportion of eels that are 
landed. Specific data on the size of eels harvested were not available, 
but 45 cm was considered a reasonable estimate (Cairns 2006b, p. 1). 
The average weight of American eels 45 cm long is 156 grams (g) (Cairns 
2006b, p. 1), which indicates that 800 metric tons is equivalent to 
over 5 million eels. Assuming a high capture efficiency of 25 percent 
for the eel fisheries (Caron et al. 2003, p. 235) suggests that the 
post-fishery abundance (i.e., 75 percent are not captured) of yellow 
and silver phase eels is greater than 15 million within the areas 
fished. Given that not all areas within the range of the eel are 
fished, this number would represent a minimum. These calculations are 
not intended to be used as a formal estimate of population size, but 
simply to provide the context that large American eels, throughout 
their range, likely number in the many millions.

(2) Trend Data From Different Life Stages and Locations

    Trends in American eel abundance from fishery-independent indices 
(e.g., data from surveys and research) varied among locations and life 
stages during the past 10-25 years. Data from yellow eels (which may 
include silver eels) and glass eels (and elvers) are presented below.
    Yellow eel. Four indices (including Maritime rivers in Canada and a 
standardized U.S. coastwide yellow eels abundance index) did not 
exhibit trends (ASMFC 2006b, p. 3). Indices from freshwater and tidal 
sites distributed from the mid-Atlantic region north to Canada and the 
St. Lawrence River indicated a statistically significant declining 
trend in yellow eel abundance at three sites. Two of these indices, 
Lake Ontario and the Chesapeake Bay index, had strong and statistically 
significant declining trends over the recent 1994 to 2004 time period, 
with 10-year declines in the order of 50 percent in the Chesapeake Bay 
index to 99 percent in the Lake Ontario indices (ASMFC 2006b, p. 3). 
Smaller declines (15 percent) were reported in the St. Lawrence estuary 
(COSEWIC 2006, p. vi). Recent data suggest that declines may have 
ceased in some Canadian locations; but the positive trends in some 
indicators for the Gulf of St. Lawrence are, the COSEWIC report states, 
too short to provide strong evidence of an increasing trend (COSEWIC 
2006, p. 58).
    It should be mentioned that yellow eel indices may reflect local or 
regional impacts, such as impacts from harvest or turbine mortality 
(see Factors B and E for further discussion). Additionally, yellow eels 
have not yet been subject to mortality that may occur during their 
oceanic outmigration to the Sargasso Sea. Therefore, yellow eel indices 
are not the best indicator for estimating annual reproductive success.
    Evaluation of the Significance of Upper SLR/LO. The extreme decline 
in eels migrating up to the upper SLR/LO, as tallied at the Moses-
Saunders eel ladder, has focused attention on the potential impact of 
that decline to the overall status of the American eel;

[[Page 4977]]

however, COSEWIC states that a rigorous way to quantify this impact to 
the overall population has yet to be developed (COSEWIC 2006, p. 35). 
The suggestion is that the reproductive contribution to the overall 
American eel population from the upper SLR/LO may be disproportionately 
larger than from other freshwater portions of the range because the 
American eels in the upper SLR/LO are almost exclusively female and 
highly fecund (producing many eggs) due to their large size, and the 
watershed is of considerable size. Two methods for estimating the 
relative reproductive contribution were presented in the COSEWIC report 
(2006, pp. 35-41), but both methods, they state, are based upon 
questionable assumptions and large uncertainties that reduce confidence 
in the results. Additionally, contributions from marine and estuarine 
waters were not considered in the analysis. According to COSEWIC some 
sources of uncertainty suggest that it is more probable that the 
methods overestimate, rather than underestimate, the reproductive 
contribution of the St. Lawrence River basin (COSEWIC 2006, p. 41).
    Glass eels. Indices of glass eel recruitment at the only two U.S. 
sites with long-term data (North Carolina and New Jersey) did not 
exhibit a declining trend over the last 14-15 years (ASMFC 2006b, p. 
4). Recruitment estimates into Canadian rivers are available for two 
Nova Scotian sites. The East River, Sheet Harbour, abundance series is 
the longest elver series available for the species. Annual recruitment 
varied without any upward or downward trend from 0.1 to 0.5 million 
elvers between 1989 and 1999 (Jessop 2003a in COSEWIC 2006, p. 28). In 
the East River, Chester, the total run of elvers peaked at 1.7 million 
in 2002. Since the overlap periods of the two series are strongly 
correlated, a combined index of 13 years was interpreted in the COSEWIC 
report. Elver recruitment showed inter-annual variability, but no 
indication of decline between 1989 and 2002 (COSEWIC 2006, p. 28).
    Glass eel counts, also called recruitment indices, are the best 
measure we have to annual reproductive success (see section immediately 

(3) Evaluation of Trend Information

    Of the available index data for the different American eel life 
history stages, we have determined that glass eel indices best 
represents the species status rangewide. Although we do not have glass 
eel indices from the entire range, the random nature of the 
leptochephali dispersal allows us to consider these data representative 
of the reproductive success of the species. As described above, there 
is not evidence of a sustained downward trend of these glass eel 
indices; therefore, we conclude that the American eel is not undergoing 
a sustained downward trend at a population level.
    In summary, the best available scientific and commercial 
information indicates that despite a population reduction over the past 
century, eels remain very abundant and occupy diverse habitats over an 
exceptionally broad geographic range. Because of the species' unique 
life history traits areas which have experienced depletions may 
experience a ``rescue effect'' allowing for continued occupation of 
available areas without concern for genetic fitness. Trends in 
abundance over recent decades vary among locations and life stages, 
showing decreases in some areas, and increases or no trends in other 
areas. Limited records of glass eel recruitment do not show declines 
that would signal recent declines in annual reproductive success or the 
effect of new or increased threats. Taken as a whole, a clear trend 
cannot be detected in species-wide abundance during recent decades, and 
while acknowledging that there have been large declines in abundance 
from prehistoric and historic times, we have determined the species 
currently appears stable.

Summary of Background

    The American eel is an extremely wide ranging species, continuing 
to occupy most of its historic range. This species is highly plastic in 
both its behavior and physiology, being able to occupy habitats ranging 
from sea water to freshwater lakes. This species also exhibits adaptive 
behaviors such as switching between habitats and diets. These life 
history characteristics provide the American eel with the ability to 
withstand a wide range of, and changing, environmental conditions. The 
best available scientific and commercial information does not indicate 
any sustained declining trend in the American eel population.

Previous Federal Actions

    On July 6, 2005, we published a 90-day finding (70 FR 38849) which 
found that the petition to list the American eel presented substantial 
scientific and commercial information indicating that listing the 
American eel may be warranted. That document initiated a status review 
to determine if listing the species was warranted. This 12-month 
finding provides the results of that status review.

Summary of Factors Affecting the Species

    Section 4 of the Act (16 U.S.C. 1533), and implementing regulations 
at 50 CFR 424, set forth procedures for adding species to the Federal 
Lists of Endangered and Threatened Wildlife and Plants. In making this 
finding, information regarding the status and threats to this species 
in relation to the five factors provided in section 4(a)(1) of the Act 
is summarized below. We examined each of these factors as they relate 
to the current distribution of American eel.
    Regional information was more obtainable from the Atlantic coast, 
likely due to the economic interest in the American eel. We have 
divided the range of the American eel into seven areas for purposes of 
discussion: (1) The Gulf of Mexico (from south Texas to the southern 
tip of Florida); (2) The Mississippi watershed (Lake Itasca in 
Minnesota to the Gulf of Mexico); (3) The U.S. Atlantic coast (the 
southern tip of Florida north to Maine's border with Canada); (4) The 
Canadian Atlantic coast (Canadian border north to Labrador, and 
including the Gulf of the St. Lawrence); (5) The St. Lawrence River and 
Lake Ontario (from the Gulf of the St. Lawrence River to and including 
Lake Ontario, abbreviated as SLR/LO); (6) The Caribbean Islands 
(Antigua, Barbuda, Bahamas, Cuba, Dominica, the Dominican Republic, 
Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, 
and Bermuda); and (7) Central/South America (Atlantic coasts of 
northern Mexico; south through Guyana, Suriname, and Venezuela; to 
northern Brazil).

Addressing Uncertainties

    The life history of American eels presents unique challenges to 
understanding the biological and environmental processes influencing 
eels at the species level. The eel's panmictic nature, wide geographic 
range, oceanic spawning, and segregation into freshwater, estuarine, 
and marine environments all contribute to the complexity of assessing 
status, threats, and whether listing is warranted. With many species, 
population dynamics modeling can inform listing determinations, but the 
current understanding of American eel population dynamics is 
rudimentary due to its complex life history and the paucity of data 
available for many key parameters, such as recruitment, growth, and 
mortality. A useful conceptual framework for a population dynamics 
model has recently been

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developed by a group of eel experts (Angermeier 2005), but quantitative 
analysis has been precluded due to a lack of data.
    As discussed below in the five factor analysis, much speculation 
exists on factors that could negatively affect eels, often based on 
effects seen on other species but with little supporting data for eels. 
Much of the uncertainty exists because decreased fitness would be 
realized during life stages that are currently not possible to assess, 
specifically, the time between adult spawning migration and the return 
of glass eels to coastal streams. For example, contaminants and swim-
bladder parasites may compromise the health of silver eels during 
migration. Contaminants could also contribute to significant early life 
history mortality, but these effects are not directly observable.
    We considered a number of questions when reviewing the available 
information and potential threats to American eel. What is the 
population status of American eel and how much caution is warranted? 
What is the species' ability to withstand threats and changing 
environmental conditions? Would all eels throughout the widely 
distributed range of the panmictic population be affected by a given 
threat? Is there evidence that indicates a threat has caused 
significant population effects, or are effects only speculative? Has 
there been a reduction in juvenile (glass eel) recruitment (which would 
signal population-level effects)? And if so, does it correlate in time 
(temporal correlation) to the appearance of a particular threat or 
threats? Answers to these and other questions are important to making a 
listing determination.
    When addressing uncertainty (not having complete, or in some cases 
any, data on one or more of the questions listed above), we employed a 
multi-step approach. The first step was to review all available data on 
the American eel with regard to uncertainty and determine, for example, 
if the data we have regarding an impact at a local or regional level 
implies an impact at a population level, and if so, what the likely 
response of the population is and in what given time period. If data 
for American eel is lacking, then we reviewed data for other Anguillid 
species, such as the European and Japanese eel, and determined if the 
application of that data was appropriate to the analysis. If 
uncertainty still remained high, then we requested individual 
assessments from experts regarding the probable implications to the 
species given the uncertainties.
    In making this finding we examined all the relevant data on 
threats, life history characteristics (such as resiliency and 
vulnerabilities), and distribution information. We explored all 
reasonable conclusions and examined information to support and refute 
theories on population level effects, looking at whether the species 
was currently showing the effects of any population level threats. A 
population level effect is defined for purposes of this finding as an 
effect that is acting in a way which puts the persistence of the entire 
species at risk. Population-level effects would be demonstrated by a 
sustained downward trend in glass eel abundance (recruitment) observed 
at index sites that represent a substantial portion of the range. Our 
five-factor analysis follows.

Factor A. The Present or Threatened Destruction, Modification, or 
Curtailment of the Species' Habitat or Range

    In analyzing these threats we assessed: (1) The relative importance 
to reproductive contribution of the various habitats occupied by the 
American eel during its life stages (such as spawning habitat in the 
Sargasso Sea, oceanic migration habitats, fresh water, estuarine and 
marine habitats), including which habitats are more likely to produce 
males or females, various growth rates, and levels of fecundity; (2) 
the threats to these habitats; and (3) the availability of that habitat 
to the American eel. Much of the information on the habitats other than 
freshwater was not available for the 90-day finding, and the new 
information has had a significant effect on our assessment of the 
status of the American eel.

Spawning and Ocean Migration Habitat

    American eels spawn only in the Sargasso Sea, and the young 
produced from that spawning utilize ocean currents to migrate to 
continental habitats where they will grow to maturity before again 
entering oceanic habitats to migrate back to the Sargasso Sea to spawn. 
Therefore, the spawning and ocean migration habitats are of vital 
importance to the persistence of this species.
    Seaweed harvest was indicated as a possible threat to the American 
eel in the ASMFC's Interstate Fisheries Management Plan for the 
American eel (FMP) (2000, pp. 6, 34). The seaweed Sargassum is commonly 
found floating in the Sargasso Sea and drifting with currents along the 
Atlantic coast from Florida to Massachusetts. Harvesting Sargassum, it 
was proposed, would affect eggs and leptocephali, if harvesting occurs 
where eggs and leptocephali are present.
    After analysis of the available data, we conclude that Sargassum 
harvest is not a threat to American eel either in the Gulf Stream 
current or in the Sargasso Sea because first, studies of larval and 
juvenile fishes associated with Sargassum found no American eel larvae 
(Settle 1993 in SAFMC 2002, pp. 20-23), and second, according to the 
South Atlantic Fishery Management Council (SAFMC), there has been no 
commercial harvest of Sargassum reported in U.S. waters since 1997. Any 
future Sargassum harvest will be highly regulated because in November 
2002, the SAFMC finalized the revised Fishery Management Plan (FMP) for 
Pelagic Sargassum Habitat of the South Atlantic Region. This plan 
specifies maximum and optimum sustainable Sargassum yield and sets 
total allowable catch limits, which severely limit Sargassum harvest 
(SAFMC 2002, pp. vi, viii). As such, we have concluded that U.S. 
commercial Sargassum harvest is not a threat to the American eel. 
Furthermore, there is no information indicating any other threat to the 
Sargasso Sea or ocean migration habitats (see Factor E for Oceanic 
Conditions), and these habitats remain abundantly available to the 
American eel.

Estuarine and Marine Habitat

    Estuarine. The importance of estuarine habitat is described by 
Helfman et al. (1984, p. 135), Jessop et al. (2002, pp. 84, 228), 
Morrison et al. (2003, pp. 93-95, 97), and Knights et al. (2006, pp. 
12-13). An estuary is a semi-enclosed coastal body of water which has a 
free connection with the open sea and within which sea water is 
measurably diluted with fresh water derived from land drainage 
tributaries. Estuarine habitat appears to not only be habitat in which 
eels may choose to remain during their continental phase, but it is 
used by freshwater residents for weight gain. According to Knights et 
al. (2006, p. 25), inshore coastal and estuarine mean net primary 
productivity (the transformation of chemical or solar energy to 
biomass) is greater than that of rivers and lakes. Females inhabiting 
estuarine waters, therefore, can provide a greater reproductive 
contribution. Estuarine habitat includes a mix of males and females. 
Because eels grow faster in estuarine waters than fresh water, the 
average age of a female within estuarine waters preparing to spawn is 
much younger (9 years of age) than females leaving lake habitats (24 
years of age in Lake Ontario). Variation in maturation age benefits the 
population by allowing different individuals of a

[[Page 4979]]

given year class to reproduce over a period of many years, which 
increases the chances of encountering environmental conditions 
favorable to spawning success and offspring survival. Jessop et al. 
(2002, p. 228) provides an interesting perspective on the relative 
production of silver eels by comparing elvers that spend 1 to 4 years 
in the estuary versus elvers that entered the river shortly after 
continental arrival. The authors suggested that the relative production 
of silver eels was 380 times higher for juvenile eels that spent 1 or 
more years in estuarine water, due possibly to lower mortality rates in 
the estuary than in fresh water (see Background, Facultative 
Catadromy). Helfman et al. (1984, p. 135), even as early as 1984, 
recognized the value of estuarine habitat where annual growing 
conditions were more favorable. Maximum size was greater in fresh 
water, but lengths at a given age were greater in estuaries. Morrison 
et al. (2003, pp. 94-95) found that annual growth rates were 
approximately 2 fold higher in brackish water when compared to annual 
growth rates in fresh water. The theory is that eels which grow faster, 
emigrate to spawn earlier.
    Although there have been historic losses and degradation of 
estuarine habitat (from, e.g., contaminants, low dissolved oxygen, 
etc.), current rates of estuarine habitat loss (nationwide) are now 
estimated at 0.9 percent (averaging 5,540 acres annually) (Dahl 2006, 
p. 16). The results of the most recent Status and Trends of Wetlands in 
the Conterminous United States from 1998-2004 became available during 
the status review. In summary, coastal wetlands are still being lost 
but at a slower rate than in prior reports. Human-caused loss of deep 
salt water in coastal Louisiana accounts for much of the recent coastal 
wetland loss (Dahl 2006, p. 16). Hurricanes can also transform coastal 
habitats, but the effects of this transformation of habitats on the 
American eel have not been studied. A U.S. Geological Service (USGS 
2006, pp. 1-2) preliminary wetland loss estimate for southeastern 
Louisiana from hurricanes Katrina and Rita, which is not included in 
the status and trends report, is the transformation of some 64,000 
acres of marsh to open water.
    From the 1950s to 1970s, substantial amounts of estuarine wetlands 
were dredged and filled extensively for residential and commercial 
development and for navigation (Hefner 1986 in Dahl 2006, p. 48). Since 
the mid 1970s, however, many of the nation's shoreline habitats have 
been protected either by State or Federal regulations or public 
ownership (Dahl 2006, p. 48).
    Channel dredging and overboard spoil disposal are common throughout 
the Atlantic coast, and changes in salinity as a result of dredging 
projects could alter the distribution of American eels. Additionally, 
dredging associated with whelk and other fisheries may damage benthic 
habitat for this species (ASMFC 2000, p. 42). Although it is likely 
that dredging and overboard spoil disposal at least temporarily degrade 
benthic habitat, we were not aware of any analysis indicating that 
these activities are a threat to the American eel.
    The two largest estuaries in North America are both on the eastern 
seaboard and support American eels: The Chesapeake Bay and the 
Albemarle-Pamlico Sound. The Chesapeake Bay and its tidal tributaries 
have over 11,000 miles of shoreline; this is more than the entire West 
coast. The Albemarle-Pamlico Sound, located in North Carolina, is the 
second largest estuary with 1.5 million acres of brackish estuarine 
waters (EPA 2006, pp. 3-4).
    Although there are limitations to the following data, as they 
include areas outside the range of the American eel, the status and 
trends report estimated that in 2004, there were slightly more than 5.3 
million acres (2.1 million hectares) of marine and estuarine wetlands 
in the conterminous United States. Eighty-six percent of that total 
area was vegetated wetland (Dahl 2006, p. 48).
    Significant estuarine areas remain from Maine to Texas. Therefore, 
this important habitat remains available to American eels, and there is 
documentation of distribution of the yellow stage of American eels 
within estuarine areas from commercial harvest data (Weeder and 
Hammond, in press, pp. 1, 6), surveys, and research data (Helfman et 
al. 1984, p. 135; Morrison et al. 2003, pp. 91-92).
    Marine. New information on marine or saltwater habitat became 
available during the status review (Daverat et al. 2006, see 
Background, Facultative Catadromy). The relative importance of marine 
habitat is not well understood, and the use of marine habitat by 
American eel for growth and maturity has only been recently confirmed. 
There was earlier confirmation in Japanese and European eel. We do not 
know what percent of the eel population inhabits strictly marine 
habitats, but eels in this habitat have high growth potential (Knights 
et al. 2006, pp. 6, 10-11), there is a predominance of females, and 
extensive habitat is available. Sasal et al. (2001 in Knights et al. 
2006, p. 12) found the female-male ratio to be 4:1 for Japanese eel 
caught in the East China Sea from 1952-1999. Knights et al. (2006, p. 
13) calculates that for the European eel in England and Wales the 
combined estuarine and marine contribution to reproduction probably 
exceeds that of fresh water. Others have also suggested that the 
percent of the American eel population living in estuarine and marine 
waters, particularly those that will contribute to future generations, 
may be quite high (Cairns 2006a, p. 1). Although there is no available 
data on the distribution of the American eels in marine waters 
throughout their range, the estimated totaled nearshore habitats (tidal 
fresh areas, through mixing areas, to seawater) are substantial. In the 
United States nearshore habitats have been estimated at 5,379 
km2 for the North Atlantic, 20,298 km2 for the 
Mid Atlantic, 12,172 km2 for the South Atlantic, and 30,604 
km2 for the Gulf of Mexico (ASMFC 2000, p. 35; NOAA 2006, 
pp. 1-3); this amounts to a total of 68,453 km2. No threats 
to the American eel in marine habitats are known to exist.

Freshwater Habitat

    Lacustrine Habitat. Lacustrine, or lake, habitat has historically 
been considered among the most important habitats for eel because some 
very well-known lake habitats, such as Lake Ontario, produce 
exclusively large, highly fecund females (Castonguay et al. 1994a, p. 
481; Casselman 2003, p. 255). Studies by Oliveira et al. (2001, pp. 
947-948) showed that the greater the amount of lake habitat within a 
watershed, the more the sex ratio favors females. There are numerous 
lakes within the distribution of the American eel, many of which have 
likely been impacted by water quality issues or exotic species 
invasions, and American eels have been denied access to some historical 
lake habitats due to barriers (see Riverine Habitat below for more 
discussion of barrier impacts) such as dams constructed in the past. We 
are not aware of new dam construction activities that are likely to 
threaten the American eel. Below we will present the information on two 
lakes, Lake Champlain and Lake Ontario that are in the Saint Lawrence 
River drainage. It has been suggested in the literature that a cause of 
declines of American eels in these lakes was barriers.
    The significance of Lake Ontario's reproductive contribution to the 
American eel was presented and discussed at a workshop (Casselman 2006, 
pp. 1-8 in USFWS 2006, pp. 8-10) and presented in the recently released 
COSEWIC Assessment and Status Report on the American Eel

[[Page 4980]]

(2006, pp. 35-41) (see Background, Population Status for further 
    Access to Lake Ontario and other Great Lakes by American eel was 
restricted to a degree by the building of hydroelectric facilities on 
the St. Lawrence River; however, the building of canals also opened new 
avenues and even provided passage past the natural barrier of Niagara 
Falls. Eels migrating into the Great Lakes and Finger Lakes basin in 
New York historically had one route through the Gulf of St. Lawrence 
and up the St. Lawrence River to Lake Ontario. Once in Lake Ontario, 
the eels could access a large number of tributaries in the United 
States or Canada, but were blocked from Lake Erie and the upper Great 
Lakes by the natural barrier at Niagara Falls. With the opening of the 
Erie Canal in 1825, and later, the New York State Barge Canal in 1928, 
a second route up the Hudson River and through the canal system was 
created, allowing eels another access route to Lake Ontario and the 
Finger Lakes (Patch 2006, p. 2).
    Although the building of the Beauharnois Dam blocked American eels 
from passing directly up the St. Lawrence River for 70 years, many eels 
were able to continue their migration through the adjacent canal--the 
St. Lawrence Seaway. Two ladders were recently constructed on the 
Beauharnois Dam, increasing the opportunities for upstream eel passage 
at that site. A second large hydroelectric dam, the Moses-Saunders Dam, 
is located 40 miles upstream from the Beauharnois Dam. From 1959 until 
1974, eels were able to pass upstream of the Moses-Saunders dam only 
through the Wiley-Dondero Canal (Verdon and Desrochers 2003, p. 140-
141). In 1974, an eel ladder was constructed on the Canadian side of 
the Moses-Saunders Dam, allowing American eels to again migrate 
directly up the St. Lawrence to Lake Ontario (Casselman et al. 1997, p. 
163), and a ladder on the U.S. side of the Moses-Saunders Dam was 
completed in 2006. These historical and recently constructed fish 
ladders are likely to benefit American eels in the SLR/LO by providing 
them with multiple opportunities to access to this drainage.
    Lake Champlain also produces predominately female eels. Declines in 
Lake Champlain were noted in the fishery in the Richelieu River (the 
river carrying about 3 percent of the fresh water from the lake to the 
St. Lawrence River). The decline has been mainly related to the 
rebuilding of two old cribwork dams on the Richelieu River in the 1960s 
(Verdon et al. 2002, p. 2) that impeded access to Lake Champlain by 
young up-migrating eels. In 1997, a ladder was retrofitted on the 
Chambly Dam to enhance eel recruitment, and in 2001, the Saint-Ours 
dam, downstream, was retrofitted with a similar eel ladder (Verdon et 
al. 2002, p. 11-12). In 1997, the total population at the foot of the 
dam was estimated at 19,650 individuals, and minimum ladder efficiency 
was estimated at approximately 57 to 68 percent. Access to Lake 
Champlain, having been reestablished, now allows American eel access to 
1,200 km2 of habitat (Verreault et al. 2004, p. 5).
    Although we are not aware of a rangewide analysis of the remaining 
amount of lacustrine habitat available to the American eel, according 
to the NatureServe data a significant amount of lacustrine habitat 
remains available to the American eel. A survey of 203 randomly 
selected lakes in eight states in the northeast United States showed 
American eel as being present in at least 20 percent of the lakes 
sampled (Wittier et al. 2001, p. 1).
    Also, efforts are being undertaken in the two large lake systems 
described above to increase American eel densities. A 10-year annual 
transfer to Lake Champlain of 0.5 to 1 million elvers from the Bay of 
Fundy (New Brunswick, Canada) is underway as an effort to improve 
abundance within Lake Champlain (Dumont et al. 2006, pp. 1-2). In Lake 
Ontario, 50,000 young eels were recently stocked as a first step in a 
Canadian multi-year plan to restore the American eel to greater numbers 
in Lake Ontario (CNEWS 2006, p. 1).
    Riverine Habitat. Riverine habitat within the range of the American 
eel is highly variable with respect to water depth, temperature, and 
flow, and habitats available. Therefore, yearly reproductive 
contributions vary among river systems. The amount of habitat, rather 
than specific types of habitat within the river, primarily determines 
how many eels a river can support (Oliveira and McCleave 2000, p. 148-
149). Both males and females are produced; densities of eels apparently 
determine the sex of individual eels, rather than habitat type (see 
Background, Sex Determination).
    Loss of access to riverine habitat has been put forward as a threat 
to the American eel (ASMFC 2000, pp. 35-39) by both decreasing 
distribution and abundance. However, most of the loss of access to 
riverine habitat occurred prior to 1960 and we have no information of 
future water development projects that threaten the American eel. Below 
we will discuss effects of the construction of dams to the eel's 
distribution first. Busch et al. (1998, pp. 1-3) conducted a 
preliminary analysis of stream habitat availability for diadromous fish 
in Atlantic coast watersheds. They reported that from Maine to Florida, 
15,115 dams have the potential to hinder or prevent upstream and 
downstream movement of fish such as eels, resulting in a restriction or 
loss of access to 84 percent of the stream habitat within the Atlantic 
coastal historic range. This constituted a potential reduction from 
345,359 miles (556,801 kilometers) to 56,393 miles (90,755 kilometers) 
of stream habitat. However, only 35 percent (5,387) of the dams from 
Maine to Florida are over 25 feet in height. The majority (65 percent 
or 9,728) are, therefore, less than 25 feet in height. Regional 
analysis of two watersheds in the South Atlantic area noted that eels 
remained present over many barriers, until those barriers reached 50 
feet in height (Cantrell 2006, pp. 4-5). Of the 15,115 dams, only 7 
percent are for hydroelectric power (Busch et al. 1998, p. 3).
    Most barriers are thought to have been in place before the 1960s. 
Castonguay et al. (1994a, p. 484) reviewed major habitat modifications 
as a potential cause for the extreme decline of American eels in the 
Lake Ontario and Gulf of St. Lawrence ecosystems. Anthropogenic (human-
caused) habitat modifications in the Lake Ontario and St. Lawrence 
River ecosystem occurred mostly before the 1960s, whereas the eel 
upstream migration decline noted at the Moses-Saunders Dam started only 
in the early to mid 1980s. Castonguay et al. (1994a, pp. 484, 486) 
proposed that the lack of temporal correspondence between permanent 
habitat modifications and the start of the regional decline evident in 
the SLR/LO argues against the role of habitat loss in the decline, as 
the decline should have been evident earlier than the 1980s. This 
assessment was tempered by the brief mention that American eels may be 
slower to respond to impacts than other fish species.
    Riverine habitats within the range of the eel can be highly 
degraded through contaminants (see Factor E, Contaminants) and changes 
in temperature, pH, and biological communities. The effect, if any, on 
eel is an increase in susceptibility in eels to disease, likely 
decreased growth (Machut 2006, p. 152; USFWS 2006, p. 27), increased 
elver mortality (Jessop 2000, pp. 523-524), and changes in behavior 
(USFWS 2006, pp. 9-10). Stream flow velocities can affect the upstream 
migration of elvers (Jessop 2000, pp. 515, 520) due to their weak 
swimming ability. However, reduced velocities due to seasonal or 

[[Page 4981]]

changes of managed flows have likely provided periods when velocities 
are passable for migration. The elver's ability to find paths around 
these velocity barriers has also been documented (elvers have strong 
climbing abilities and can negotiate vertical barriers) (Jessop 2000, 
p. 520; Craig 2006, pp. 2-4).
    Impacts of barriers on distribution: When discussing impacts of 
barriers on distribution, we will cover impacts at three levels: (1) 
Rivers, (2) watersheds, and (3) the American eel's entire range.
    At the level of individual rivers, the impact of barriers can range 
from very little impact to local or regional extirpation. This is 
because the effect of barriers on eel upstream migration appears to be 
site-specific. For example, a steep vertical barrier has a different 
effect on elvers, which can climb, than on yellow eel, which do not 
have the same climbing ability. Therefore, the location of the barrier 
along the river and in the watershed will dictate its impact (USFWS 
2005b, p. 16). Additionally, the level of impact is also affected by 
the type of barrier (i.e., hydroelectric dam, weir, old mill dam, or 
dam for recreation, water supply, or navigation), as well as how the 
barrier is operated (if there is spill water), its general condition 
(those in poor repair are more likely to have rough areas or spillage, 
both better for eel), whether it was equipped with eel or other fish 
passage, and other site specific conditions (Goodwin and Angermeier 
2003, pp. 532-533; USFWS 2005b, pp. 16-19). Indeed Busch et al. (1998, 
p. 3) originally suggested that site-specific assessments would be 
required when further analyzing the impacts of barriers to the American 
eel, and that their estimate of 84 percent loss of freshwater habitat 
for the American eel was a gross estimate, provided as a starting point 
for future scientific studies.
    Our additional research into eel distribution shows that eels 
remain widely distributed within most of the watersheds historically 
inhabited by the American eel. For example, Jacobs et al. (2004, pp. 
325, 330), in a Connecticut watershed survey, verifies the presence of 
American eel above barriers and a current extensive distribution. 
American eel were the most ubiquitous species of all fish species 
sampled in the Connecticut River drainage, present in 97 percent of all 
sites sampled and common in both the main stem rivers and tributary 
streams (Jacobs et al. 2004, p. 325). Machut (2006, p. 49), in his 
study of Hudson River tributaries, found that American eels are the 
most numerous fish within the tributaries surveyed.
    To better understand the impacts of historically constructed 
barriers on eel upstream migration and potential loss of habitat we 
analyzed three watersheds we think are representative of the U.S. range 
of the species.
    The Mississippi Watershed. The American eel persists in the 
Mississippi watershed (Mississippi River and the tributaries of the 
Missouri, Arkansas, Ohio, and Tennessee Rivers), albeit having likely 
declined in abundance during the past half century (Becker 1983, p. 
258). Very little data exists on the abundance of the American eel 
within the Mississippi watershed (Ickes et al. 2005, p. 4), both 
historically and currently, as eels are not typically targeted during 
studies and are likely underestimated. The Long-Term Resource 
Monitoring Program (LTRMP) conducted by the Upper Mississippi 
Environmental Sciences Center (UMESC) observed 75 eels out of nearly 
four million fish collected from 1993-2002 (Ickes et al. 2005, p. 9).
    The distribution of the American eel remains widespread in the 
Mississippi watershed even though it was anticipated by Coker (1929, p. 
173) that the American eel, in time, would cease to exist in areas of 
Minnesota, Wisconsin, and Iowa, due to the construction in 1913 of the 
Keokuk Dam, or Lock and Dam 19, in Keokuk, Iowa (River Mile 364). The 
barriers on the Mississippi River mainstem are mainly navigation locks 
and dams in the upper portion of the river. These navigation locks and 
dams were built to hold back water and form deeper navigation ``pools'' 
while allowing for barge passage through the locks. Presumably, these 
lock and dam complexes allow for eel passage when barges pass (Cochran 
2005, p. 2) or eels pass during high water stages, as American eel are 
still found above Keokuk Dam today. The Keokuk Dam is currently the 
tenth dam eel encounter during their upstream migration on the 
Mississippi River.
    South Atlantic-Pee Dee River and Santee River Basins, North 
Carolina and South Carolina. American eels continue to be distributed 
throughout the lower areas of these watersheds, indicating they are 
able to negotiate certain barriers and persist within this historic 
habitat. Of the six dams in the Santee and Pee Dee River basin, eels 
are able to pass four (Cantrell 2006, p. 3). They are prevented from 
reaching their extreme headwaters where they had historically been 
reported as ``everywhere common'' by Jordan (1889, p. 139). Large (over 
50 feet) hydroelectric and other dams likely impede upstream movements 
of elvers and subadult eels to these historic habitats.
    Androscoggin and Kennebec River Basins, Maine and New Hampshire. 
Our knowledge of current distribution of American eel for the 
Androscoggin and Kennebec watersheds of Maine and New Hampshire is 
based on a systematic survey in 2002 and 2003, and supplemental 
electrofishing survey data (Yoder et al. in preparation, pp. 1-7). 
Presence of fishways on dams; dam leakage, height, configuration, 
materials, and location up the river relative to the size of eel; water 
quality issues; and presence of lakes (which may be of more interest to 
eels due to odor cues) are thought, by Wippelhauser, to play a role in 
the distribution differences within the two watersheds and explain why 
eels are more abundant in the Kennebec watershed (2006a, p. 1).
    The American eel remains present above the first dams encountered 
inland, as well as subsequent barriers, up to the Gulf Island Dam on 
the Androscoggin (approximately 52 river miles) and the Wyman Dam on 
the Kennebec (approximately 122 river miles), with anecdotal 
information indicating that abundance has decreased (Adams 1992, p. 
    Rangewide our analysis of the impacts of barriers was limited to 
the information available, that of North America. An update of 
NatureServe's distribution map (Figure 2) includes the American eel 
freshwater distribution information we received from most States within 
the species' historic range as well as from Canada and a few of the 
Caribbean Islands, along with NatureServe's existing database.

[[Page 4982]]



[[Page 4983]]

    At the scale analyzed, the American eel remains distributed over 
roughly 75 percent of its historic native range within U.S. watersheds 
(Castiglione 2006, pp. 1-5). Figure 2 represents the historic 
(291,416,355 hectares) and current distribution (163,781,049 hectares) 
of the American eel within its native freshwater habitat in the United 
States. Additionally, Figure 2 identifies the area where the eel was 
introduced and is considered currently present, an addition of 
2,921,343 hectares (Castiglione 2006, pp. 1-5).
    The watershed examples provided earlier are indicative of the 
relationship of barriers and eel distribution throughout the species' 
range in North America. From these examples, and the data from 
NatureServe, we conclude that not all structures (natural or human-
made) considered barriers to other fish species should be thought of as 
barriers to the eel. We also conclude that there are dams, other human-
made structures, and some natural features that are complete barriers 
to American eel. In the case of human-made structures, those structures 
have reduced the historical range of the American eel.
    The fate of eels that are unsuccessful in passing a barrier is 
unknown, but it has been speculated that eels may find alternative 
habitat, that overcrowding below the barrier may increase the 
likelihood the eels will become male, and that below the dams there is 
likely increased competition, reduced food availability negatively 
affecting growth rates, and predation (USFWS 2005b, p. 19; Machut 2006, 
p. 53).
    Impacts of barriers on density: Whereas general fish surveys can 
provide American eel distribution data, few studies address the changes 
in eel density (also called abundance) due to barriers. Goodwin and 
Angermeier (2003, p. 533) found that dams can exacerbate the decline in 
eel density; however, this is clearly the case for only one in three 
dams within their study area. Machut (2006, p. 51) found in the Hudson 
River watershed, where there are almost 800 barriers, that the first 
barrier encountered dramatically reduces eel densities, but did not 
necessarily result in local extirpation. Densities were highest below 
barriers, while age, growth (in length), and the number of females 
increased above barriers.
    Two aspects of the eel's life history add complexity to 
understanding the true impact that decreased density may have on eel 
reproductive contribution. Densities decrease naturally with distance 
from the Continental Shelf (see Background), while relative female 
fecundity increases with lower density (see Background). Based on these 
factors, we conclude that low upstream abundance is a natural 
phenomenon exacerbated to varying degrees geographically by human-made 
structures and natural barriers, but that relative reproductive 
contribution is not lost in direct proportion to the decrease in 
density (see Background, Distribution Clines). Additionally, we 
conclude that when taking into consideration or trying to quantify the 
impact of barriers on the American eel, site-specific information on 
the barrier is critical, as is analyzing the historic sex ratio of an 
area, the dynamic between lower abundance and the higher probability 
that females will be produced, density-dependant growth relationships, 
and length-fecundity relationships. Unfortunately, the information to 
conduct this comprehensive analysis is not available.
    The availability of riverine habitat can be seen in Figure 2, and 
also be looked at in terms of kilometers of riverine habitat unimpeded. 
Unimpeded freshwater habitat (riverine kilometers downstream of 
terminal dams, the dams closest to the ocean) in each river also 
remains available to the American eel. In the United States alone, from 
Texas to Maine (not including the Great Lakes), there remains over 
590,000 km of freshwater habitat available to American eels downstream 
of terminal dams or within rivers that do not have significant barriers 
(such as the Delaware River). An example of this downstream available 
habitat on a watershed basis is the 1,153 river miles available on the 
Connecticut River downstream of the terminal dam, including both the 
mainstem and tributaries (Castiglione 2006, p. 1-2).
    In our analysis, we found that the distribution of the American 
eels has not been significantly reduced by barriers, as many barriers 
do not preclude upstream migration of the American eel. Some dams 
appear to form a complete barrier to upstream migration, potentially 
responsible for the reduction in available freshwater habitat of 
approximately 25 percent. Further, distribution is far less affected by 
barriers than is density. If there were population level effects from 
this decrease in American eel distribution or density in maturation 
habitats, there would be corresponding declines in the recruitment of 
juvenile eels; however, this is not the case (see Background, 
Population Status).
Summary of Factor A
    Spawning and ocean migration habitats are essential to the 
persistence of the American eel; there are no apparent human-caused or 
significant threats to these habitats; and, they remain available and 
occupied by the American eel.
    Estuarine, marine, and freshwater habitats provide maturation 
habitat for the American eel, and new information verifies that some 
portion of the American eel population completes its lifecycle without 
ever entering fresh water. Of these maturation habitats, freshwater 
habitat has been the most impacted by human-caused actions such as 
barriers (i.e., dams constructed for hydroelectric, water supply, and 
recreation purposes), most of which we would consider historic losses; 
in which case population level impacts have likely been mostly 
realized. We are not aware of future dam construction which is likely 
to cause significant impact to the American eel. We have concluded that 
although some dams appear to form a complete barrier to upstream 
migration and likely caused the regional extirpations seen in 25 
percent of the eel's historic freshwater habitat, American eels are 
able to negotiate many barriers. This has allowed the American eel to 
remain well-distributed throughout roughly 75 percent of its historic 
freshwater range, mainly in the lower reaches of watersheds. American 
eel abundance has been affected by barriers to a greater degree than 
has distribution; however, there is no evidence that the reduction in 
densities has resulted in a population level effect, such as a 
reduction in glass eel recruitment. Analyses of local and regional 
declines in abundance do not temporally correlate with the loss of 
access to habitat.
    The status of the American eel and the effects of freshwater 
habitat loss must be examined in light of the American eel's habitation 
in fresh, estuarine, and marine habitats. Highly fecund females 
continue to be present in extensive areas of fresh water (lacustrine 
and riverine) and estuarine and marine habitats; males also continue to 
be present in these habitats. Recruitment of glass eels continues to 
occur in these habitats with no evidence in reduction in glass eel 
recruitment. For these reasons, we believe the available freshwater, 
estuarine, and marine habitats are sufficient to sustain the American 
eel population.

Factor B. Overutilization for Commercial, Recreational, Scientific, or 
Educational Purposes

    In analyzing the threat of overutilization, we focused primarily on 
recreational and commercial fisheries on the U.S. Atlantic coast and in 
Canada because these fisheries are the most

[[Page 4984]]

active. We will briefly characterize these two fisheries and discuss 
recent changes, summarizing the pertinent scientific and commercial 
information. For detailed descriptions of United States and Canadian 
fisheries (e.g., harvest restrictions by State), see the 90-day finding 
(July 6, 2005, 70 FR 38849) or ASMFC 2006a (pp. 11-20) and for Canada's 
fishery, see the COSEWIC report (2006, pp. 46-48). We will begin, 
however, with a short discussion of the factors that drive the 
commercial harvest of Anguillid eel.

Commercial Fishery (Including Bait Fishery)

    Eels (most notably Japanese and European eels) are popular seafood 
in Europe and Asia, particularly Japan, and to a much lesser degree in 
North America. At this time, fish culturists have not been able to 
provide the conditions necessary for eels to reproduce and mature in 
captivity; therefore all eels consumed or used as bait are taken from 
the wild. Some of the eels taken from the wild as glass eels or elvers 
are grown out to maturity in aquaculture facilities.
    The commercial eel harvest both here or in other countries is 
driven in large part by the international demand for eel (see Pawson et 
al. 2005 for discussion of international eel market), yet American eel 
represent but a fraction of the total international trade in eels. 
China appears to be setting the world price by both buying eels on the 
international market and producing eels in extensive aquaculture 
facilities (Dekker 2005, p. 2). According to TRAFFIC, a joint program 
of the World Wildlife Fund and the World Conservation Union (IUCN), 
over 90 percent of the world's eel aquaculture yield takes place in the 
Asian countries of Japan, Taiwan, and mainland China (TRAFFIC 2002, pp. 
11-12). Between 1998 and 2004, China supplied two-thirds (i.e., 
approximately 130,000 metric tons) of the world's cultured eel 
production. The species used in aquaculture in Asian countries consists 
primarily of European and Japanese eel. According to the United 
Nations' Food and Agriculture Organization (FAO), even with increasing 
dependence on European and American glass eels for aquaculture purposes 
with the decline of Japanese eels (TRAFFIC 2002, pp. 13-14), American 
eels represent only about 5 percent of the overall worldwide yield of 
Anguillid eels (OLE 2004, p. 1; FAO in Dekker 2005, p. 3). The 
insignificant contribution to the worldwide eel trade indicates that 
the American eel harvest is unlikely to be appreciably affected by 
changes in international markets.
    Commercial harvest of the American eel in North America occurs 
mostly along the Atlantic coast of the United States and Canada. In the 
United States, the commercial fishery occurs mainly in the Chesapeake 
Bay with smaller fisheries scattered throughout other States. All 
continental life stages are harvested commercially, but regulations 
restrict harvest so that exploitation of life stages differs 
geographically. American eel fisheries are unevenly distributed within 
Canada. In some regions, there are intensive fisheries, while in other 
regions, eels are unexploited. All continental stages are harvested 
commercially in Canada, but the stages that are exploited vary 
geographically (COSEWIC 2006, pp. 46-47). Limited commercial fisheries 
exist in Mexico and some Caribbean islands (ASMFC 2006a, p. 14). No 
glass eel or elver fishery exists in the Gulf of Mexico (ASMFC 2000, p. 
    Exploitation rates (the percent of mortality associated with 
harvest) vary with the life stage, fishing gear, and other factors. 
Glass eels and elvers are typically harvested as they ascend rivers and 
estuaries. One study suggests an exploitation rate of 30-50 percent of 
arriving elvers (Jessop 2000, p. 523). If there was no density-
dependent change in sex ratio, growth, survival, or emigration rate in 
subsequent stages, the reduction in egg production due to the elver 
fishery would be equivalent to the percent elver exploitation described 
above. However, such density-dependent effects are believed to occur 
(ICES 2001, p. 34). In other words, the relatively high exploitation 
rate for glass eels and elvers does not translate to that level of 
reproduction loss because the glass eels and elvers that are not 
harvested have a greater potential for survival and, therefore, 
reproduction. Elver fisheries, it has been suggested by Jessop (2000, 
p. 523), may be biologically justified to a greater degree in Nova 
Scotian streams with low pH, given the abundance of elvers entering 
these streams and the high mortalities that occur during their first 
summer in fresh water (rather than in more productive streams with 
higher pH values).
    Silver eels are exploited in rivers mainly in weir fisheries and in 
coastal waters with eel pots. In the St. Lawrence estuary silver eel 
fishery, mark-recapture experiments estimated exploitation rates of 19 
percent in 1996, and 24 percent in 1997 (Caron et al. 2003, p. 239).
    In the Chesapeake Bay, the estimated exploitation rate is something 
less than 25 percent. The data collected did not separate exploitation 
rates for yellow eels harvested in the pot fishery from eels that 
naturally emigrated from the area. This combined fishing mortality and 
emigration was estimated at 25 percent, significantly lower than the 
Prince Edward Island fishery presented below (ICES 2001, p. 34).
    Data from Prince Edward Island, Canada, were used by the authors of 
the ICES report (2001) to calculate yellow eel exploitation rates. They 
estimated an approximately 50 percent rate of exploitation in estuary 
and tidal waters (ICES 2001, p. 41). The authors also estimated how 
this rate of exploitation would be expressed in loss of reproductive 
contribution, but based on some significant assumptions, they consider 
the estimate preliminary. They suggest the effect on reproduction would 
be a decrease of approximately 90 percent, based on the premise that 
the largest, and hence most fecund, females are targeted. However, they 
also note that the estimated reduction in reproduction for the entire 
Prince Edward Island area would be less than this value, because there 
is no eel fishery in non-tidal waters, and there is minimal fishing 
effort in the central and western portions of the Northumberland 
Strait, which amount to about one third of the Prince Edward Island 
coastline (ICES 2001, pp. 34-35).
    Exploitation rates are lacking for most of the range where the 
American eel is harvested, but the above examples show how complex 
estimating exploitation rates is, given that factors, such as areas 
unfished, need to be accounted for when evaluating harvest effects on a 
species rangewide.
    The American eel fishery has changed over time. Harvest, or 
landings, were significantly higher in the 1970s (Figure 3), presumably 
as a result of demand for glass eels for the newly emerging aquaculture 
industry in China (St. Pierre 1998, p. 1), which inflated prices and 
made eel fishery profitable. Landings have declined in the United 
States and Canada since then; however, the reason for the decline in 
landings appears multifaceted.

[[Page 4985]]


    The price per pound fluctuates considerably for American eel, 
thereby affecting landings. For instance, the Chinese aquaculture 
market still requires glass eels to maintain the established 
aquaculture business (Moriarty and Dekker 1997 in ASMFC 2006a, p. 6), 
but when available, the Chinese buy Japanese glass eel, which is the 
eel preferred by Asians. Consequently, the price for American eel has 
dropped. ASMFC (2006, p. 7, 12-13, 43) also lists poor market 
conditions as likely responsible for more recent reductions in all 
commercial eel fisheries. Since 1998, glass eel market prices have 
fluctuated from $300 per pound (1998), to $10-$15 per pound in 1999, to 
$105-300 per pound in 2005, to $60 per pound in 2006 (Wippelhauser 
2006b, p. 1).
    License requirements and State-regulated size and catch limits have 
also played a role in the decline seen in landings (ASMFC 2006, p. 43). 
In 2000, the ASMFC (the agency regulating harvest along the U.S. 
Atlantic coast), responding to the concerns of fishers, scientists, and 
resource managers that American eel had declined from historic levels 
and that assessment data was limited, implemented a Fishery Management 
Plan that required States to establish minimum size limits for 
commercial eel fisheries.
    Trends in Canadian eel fishery. In Canada, there has been a trend 
towards increasingly restrictive fishing regulations in the last 
several decades, especially in the Atlantic Provinces, and especially 
since 2000 (Cairns et al. 2005 submitted in COSEWIC 2006, p. 48). This 
could translate, we believe, to a decline seen in Canadian landings 
data. Changes include shortening of seasons, increases of minimum size, 
caps on the number of fishing gear that can be deployed, and freezes on 
development of any new American eel fisheries (COSEWIC 2006, p. 48). 
There was a buy-out of 50 percent of commercial licenses at Lake St. 
Pierre, the fishery in the Richelieu River was closed in 1998, and the 
fishery in the upper SLR/LO was closed in 2004 (OMNR 2004, p. 1). Glass 
eel and elver fishery only exists in the Scotia-Fundy area of the 
Maritime Provinces and occurs during narrow time windows (COSEWIC 2006, 
pp. 46-47).
    Trends in United States glass eel and elver eel fishery. During the 
lucrative early 1970s, Florida, North Carolina, South Carolina, 
Virginia, Massachusetts, and Maine developed glass eel and elver 
fisheries. By 2002, all Atlantic coast States except Maine and South 
Carolina had restrictions on harvestable eel size or fishing gear that 
restricted glass eel and elver fishery (ASMFC 2006a, pp. 12-18). One of 
those remaining States, Maine, began in 1999 to limit glass eel

[[Page 4986]]

and elver harvest through emergency legislation with a limited entry 
system, restrictions in fishing gear, restrictions on locations, and a 
reduced length of the season (March 15-June 15). This later requirement 
allows for one or more months in winter when glass/elvers are not 
harvested. The emergency legislation reduced fishing effort in Maine by 
at least 79 percent (ASMFC 2005, p. 18), ensuring that a significant 
run remains in Maine waters. Maine was the only State reporting glass 
eel and elver landings in 2004, at approximately 0.5 metric tons, down 
from 7.53 metric tons in 1995, and 9.98 metric tons in 1977. South 
Carolina and Florida permit glass eel fishery, but it is not active 
(ASMFC 2005, pp. 5, 14).
    Trends in United States yellow and silver eel fishery. Currently a 
yellow and silver eel fishery exists to varying degrees in all States 
and jurisdictions along the Atlantic coast except Pennsylvania and the 
District of Columbia. South of Maine, the yellow and silver eel fishery 
seems to be primarily coastal pot fisheries, and different States have 
varying regulations, if any, imposed on this fishery. In Maine, the 
yellow and silver fishery occurs in both inland and tidal waters (ASMFC 
2006a, pp. 19-20). The Maine fishery has declined since 1998 because of 
legislation and poor market conditions, with prices paid declining from 
$3-$4 per pound to $1.25-$1.75 per pound. Harvesters report that the 
low prices are due to eels being grown out in aquaculture facilities in 
Canada (Knights 2003, p. 242). Eels grown out in an aquaculture 
facility, a fish company representative suggests, are better suited to 
smoking, due to their high fat content and uniform size and shape. The 
uniform size is better suited for the current mechanized processing 
(Feigenbaum 2005, p. 12). The decline in effort may encompass other 
areas along the Atlantic coast as well (ASMFC 2006a, pp. 13-14). For 
example, on the northern shores of New Jersey, the number of active 
fishers has declined from 16 in 1980s to 0 in 2004 (Feigenbaum 2005, p. 
    In characterizing the future impact of harvest, the literature 
supports the prediction that 1970s harvest levels are unlikely to occur 
again due to the changes in the market (Pawson et al. 2005, p. 6; 
Dekker 2005, p. 2), including the interest in eels raised in 
aquaculture facilities rather than wild caught eel, due to ease of 
processing (Feigenbaum 2005, p. 12); the implementation of harvest 
regulations (ASMFC 2006a, p. 43); and the retirement of eel fishers 
(Wippelhauser 2006b, p. 1).
    Population level impacts. In assessing population level impacts of 
commercial fishing on American eels, we took into account both the 
species' resiliencies and vulnerabilities, and levels of exploitation, 
including a review of fished versus unfished areas in the species' 
range, and whether there is evidence of a population level impact.
    Resiliencies include the following: (1) The wide range of the 
species, which leaves many areas without fishing pressure (USFWS 2005b, 
pp. 69-70, 76; COSEWIC 2006, pp. 46-47, 53; Cairns 2006c, pp. 1-3); (2) 
harvesting within an area is unlikely to substantially affect the 
replenishment of the area through recruitment (to the degree it might 
with fish species that have river specific stocks) because of the 
random nature of recruitment (see Background section and Factor E Ocean 
Conditions); (3) harvesting will not affect genetic variability because 
the species is a single population; (4) eels have relatively high 
fecundity rates; and (5) the species possesses general plasticity and 
robustness (Knights 2005 in USFWS 2005b, pp. 50-59); also see 
Background for further explanation and citations). Conversely, 
vulnerabilities include the following: (1) All eel harvest takes place 
before the species has had an opportunity to spawn, and American eel 
only spawn once; (2) all continental life stages and multiple year 
classes are subjected to harvest in some portions of the species' 
range; and (3) harvest of large individuals unequally affects females 
(eels below 40 cm in length are either male or female, but almost all 
eels greater than 40 cm are female) (ASMFC 2000, p. 2; USFWS 2005b, p. 
    Although we have data on landings (harvest) of American eel, we 
lack specific data on fished versus unfished areas over the range of 
the American eel. Recent mapping by Cairns and others (2006c, p. 3) has 
begun to identify (but not yet quantify) fished versus unfished areas 
in Canada, but initial results suggest that much of the Canadian range 
of the American eel is unfished (COSEWIC 2006, pp. 46-47, 53). In 
Canada, there is little eel fishing effort in the Gulf of Nova Scotia, 
and none in most fresh waters of the southern Gulf of the St. Lawrence 
River. Many rivers and coastal areas in the Scotia-Fundy area of the 
Maritime Provinces are unfished and Newfoundland and Labrador have 
rivers which are not exploited. Additionally, there are the areas of 
harvest closure including the Richelieu River and Lake Ontario (Cairns 
2006c, pp. 1-3).
    Although we do not have similar mapping in the United States, there 
are considerable areas within the species' range that are not subject 
to harvest. Commercial eel harvest is either prohibited (such as in 
Tennessee, Todd 2006, p. 1) or at low levels in States within the 
Mississippi watershed (Keuler 2006, p. 1) and the U.S. portion of the 
Great Lakes (Lutz 2006, p. 1). Although the ASMFC was unable to provide 
fished versus unfished areas along the Atlantic coast, a fish company 
representative who works with the fishers was able to confirm that 
there are areas along the Atlantic coast which support eels and are not 
now being exploited (Feigenbaum 2006, p. 6).
    Modeling exercises have indicated that harvest has depleted the 
abundance of eels in the Chesapeake Bay, where approximately 50 percent 
of the U.S. yellow eel landings occur (Weeder and Uphoff, in press, pp. 
6-7). Modeling conducted by BEAK (2001, pp. 31, 5.1, 5.7) for the 
purposes of prioritizing factors influencing eel abundance, ranked 
fishing mortality on yellow and silver eels as the number one factor 
with regards to American eel abundance in the upper SLR/LO. The upper 
SLR/LO was an area of substantial harvest beginning in the 1970's, with 
a peak in 1978 of 230 metric tons (Robitaille et al. 2003, p. 258). 
Commercial harvest in the upper SLR/LO closed in 2004.
    At a population level, however, one must take into account existing 
regulations and exploitation rates that allow for: (1) A level of 
individuals who are not subjected to fishing pressure; (2) the theory 
that fishing of glass eels and elvers does not necessarily represent a 
substantial loss to reproductive capacity of the species; (3) the vast 
areas that remain unfished; and, (4) the lack of evidence that there is 
a reduction in glass and elver recruitment rangewide (which would be 
the indicator of overharvest) (see Background, Population Status). 
Taking all these factors into account, we have determined that 
commercial harvest currently affects the American eel only at a local 
or regional level.

Recreational Fishery

    Recreational harvest is either limited or nonexistent throughout 
most of the range of American eel. Eels are likely purchased or caught 
by recreational fishermen for use as bait for larger gamefish such as 
striped bass (USFWS 2005b, p. 74; ASMFC 2005, p. 6), and the remainder 
is mostly catch and release (ASMFC 2005, pp. 5-6). The NMFS Marine 
Recreational Fisheries Statistics Survey (MRFSS), which has surveyed 
recreational catch in ocean and coastal waters since 1981, shows a 
declining trend in the recreational catch of eels during the latter 
part of the

[[Page 4987]]

1990s. In 2003, total recreational catch was 156,381 eels, and in 2004, 
112,001 eels. In 2004, the combined catch from New Jersey and Delaware 
represented 40 percent of the recreational American eel catch, and the 
combined catch from New York and Delaware represented 62 percent of the 
recreational American eel harvest. About 79 percent of the eels caught 
were released alive by the anglers in 2004 (ASMFC 2005, p. 6).
    To protect American eel from unregulated recreational harvest, all 
ASMFC member States were required to establish uniform size (6 inches) 
and possession limits (maximum 50 eels per person per day) for 
recreational fisheries, and recreational fishermen are not permitted to 
sell eels without a State license that specifically authorizes this 
activity (ASMFC 2006a, p. 17). After a review of the best available 
scientific and commercial information, it does not appear that 
recreational harvest poses a significant threat to American eel.
    There is little information in the literature on subsistence 
harvest and bycatch. But according to Laney (2006, p. 1) and others 
(USFWS 2005b, p. 14, 79), bycatch of eels in marine waters, during 
harvest for other targeted fish species, does not appear to be of 
concern for the American eel. This is likely due to the fishing gear 
used in these other fisheries (Laney 2006, p. 1). Fisheries utilizing 
trawl gear may catch eels, depending on the size of the netting. 
Netting of a \1/2\ inch and 1 inch used in the late 1960s did catch 
eel, but only a handful (Wenner 1973, p. 1). Modern netting size is 
more specific to the targeted fish species in an attempt to limit 
Summary of Factor B
    In conclusion, there are no data to suggest that subsistence 
harvest, bycatch, and recreational harvest are having a significant 
impact on American eel regionally or rangewide. Future commercial 
harvest of American eel is not anticipated to reach 1970s levels, and 
we find it unlikely that American eel landings will increase 
significantly by future changes in the international market.
    Commercial harvest has had a strong influence on eel densities in 
some local and regional areas, but we see no evidence that commercial 
harvest is having an effect at a population level. A population level 
impact would be seen in declines in juvenile recruitment rangewide, yet 
this is not in evidence. It is probable that: (1) The random dispersal 
of the larval stage enables the species to successfully recruit to 
other areas, including extensive unfished areas, throughout its range, 
thereby buffering the effects of harvest; (2) the compensatory 
mechanism of the increasing probability of glass eel and elver 
survival, or of undifferentiated eels becoming female, as densities 
decrease provide this species with some level of resilience; and, (3) 
current exploitation rates and regulations insure that substantial 
numbers of eels remain unfished. These factors are likely sufficient 
enough to maintain the species as a whole even under foreseeable 
fishing pressure. As such, we have determined that harvest is not a 
significant threat to the American eel at a population level.

Factor C. Disease or Predation

    In our analysis of diseases and predation, we focused on the 
diseases and types of predation that were most likely to affect the 
American eel at a population level.


    We evaluated changes in predation as a result of human-caused 
activities. It had been suggested in the 90-day finding that American 
eels blocked or delayed at upstream barriers could experience higher 
than normal mortality rates due to predation, because birds of prey and 
piscivorous fish often congregate at the base of dams to prey on other 
fish species (USFWS 2005b, p. 20). However, we found nothing more than 
anecdotal information on this topic, and therefore we were unable to 
quantify the impact of predation as a result of barriers. Natural 
predation rates are likely very high for elvers upon entering 
freshwater (see Background, Juvenille Mortaltiy and Jessop 2000, p. 
522), but there is no evidence to indicate that natural rates of 
predation have risen, or that eel population numbers are approaching a 
diminished level where natural predation rates pose an increased risk 
to the eel rangewide (USFWS 2005b and 2006).


    We analyzed whether the spread of fish diseases, and in particular 
parasites, has accelerated due to human activities, including global 
transport of fish for aquaculture, and whether the threat of disease 
presented a risk to the American eel at a population level.
    Parasites. The parasite of most concern is the nonindigenous 
nematode Anguillicolla crassus, a parasite with five life stages that 
becomes sexually mature in the swimbladder of the eel. The only other 
parasite found in the eel swimbladder is another nematode, Daniconema 
anguillae (Moravec and K[oslash]ie 1987 in Kirk 2003, p. 387), but it 
rarely occurs in high numbers (Kirk, unpublished observations in Kirk 
2003, p. 387).
    Although there is no direct evidence that A. crassus prevents 
Anguilled eels from completing their spawning migration or influencing 
the silvering process, hypotheses, such as those of Kirk 2003, have 
suggested that A. crassus may impair the capacity of the eel to 
undertake the migration to the Sargasso Sea. Presented below is the 
history of invasion by A. crassus, percentage of American eels 
infected, the known physiological effects on Anguilled eels from A. 
crassus, hypotheses regarding impacts to outmigrating silver eels, and 
our analysis of the data.
    Native to Japanese eel, A. crassus invaded wild populations in 
Europe, most likely through aquaculture, around 1982, and in North 
America (Texas) about 1995, again likely a result of transported eels. 
Since then, the U.S. invasion by A. crassus has spread north along the 
Atlantic coast. By 1997, 10 to 29 percent of the American eels in the 
Chesapeake Bay were infected by A. crassus, and by the year 2000, 
greater than 60 percent of the American eels in the freshwater portions 
of the Hudson River, New York, were infected. The known northern extent 
of the parasite at this time is the Sedgeunkedunk Stream in Maine 
(USFWS 2006, p. 2). Although it has not yet been detected in Canadian 
waters, it is believed that A. crassus is likely to spread to Canada in 
the future, potentially through aquaculture, because there do not 
appear to be limiting factors for the parasite spreading farther north 
(USFWS 2006, p. 2, 7). Temperature is apparently not a limiting factor 
(although temperatures at or below 4 [deg]C slow infection rates), nor 
is salinity (although rates of infection have been shown to be lower in 
brackish waters), and the parasite has now been found in all size 
classes of eel (Oliviera 2006, pp. 1-20, in USFWS 2006, p. 2).
    An aspect that may aid in the spread of the parasite is the number 
and variety of intermediate hosts (currently 12 families, both fish and 
invertebrates, are known to serve as intermediate hosts). However, 
physical barriers, such as dams and natural waterfalls, which likely 
preclude movement of intermediate hosts, have been shown to 
significantly reduce infections of eels upstream beyond the second 
barrier (Machut 2006, pp. 75, 81-82). Also the expulsion of ballast 
waters may be providing transport for the parasite. Recent research 
indicates rivers with large ports have the highest rates of infection, 
leading researchers to the conclusion that ballast water may

[[Page 4988]]

explain continued invasion (Oliveira 2006, p. 19 in USFWS 2006, p. 2). 
Another recent finding is that urbanization may increase susceptibility 
to infection. Elevated infection rates were present when urbanized 
lands exceeded 15 percent (Machut 2006, p. 82).
    The percentage of American eels infected by A. crassus can vary 
significantly. In one North Carolina study the percentage of American 
eels infected ranged from 10 to 100 percent, between sites studied 
(Moser et al. 2001, p. 1). Hypotheses suggested to explain this wide 
range in American eel infection rates include: (1) Eels occurring near 
large shipping ports will have more exposure to exotic parasites, 
possibly as a result of infected intermediate hosts being transported 
by ballast water; (2) warmer waters are equated with higher prevalence 
of parasitic infection; and, (3) the longer a watershed has been 
infected, the higher the anticipated infection rate (USFWS 2006, p. 1-
    Although A. crassus infection causes physiological damage to the 
swimbladder, this damage is not much of a concern except for silver 
eels during outmigration. There is no apparent detrimental effect on 
eel weight and length in the yellow eel stage, but the demands on the 
swimbladder, which assists in buoyancy and depth control, would be 
greatest during outmigration because the eel may use deeper waters on 
its trip back to the Sargasso Sea to spawn. The parasite typically 
lives for several months and therefore likely persists during 
outmigration (van den Thillart et al. 2005, pp. 7, 233; USFWS 2006, p. 
2). According to Knopf and Mahnke (2004, p. 494), Japanese eel are not 
affected by A. crassus to the degree that a non-adapted host, such as 
the European eel (and presumably American eel) is because the Japanese 
eel possesses more effective defense mechanisms against A. crassus, 
likely due to the co-evolution process which resulted in a balanced 
host-parasite system without significant harm to the host. Kirk (2003, 
pp. 390, 391) presents studies suggesting there may be a level of 
immunity that develops in the non-adapted hosts.
    Laboratory studies in the European eel, have shown that light 
(approximately 5 nematodes per eel) and moderate infections can reduce 
eels' swim capacity, perhaps by as much as 10 percent (Sprengel and 
Luchtenberg 1991 in Moser et al., 2001, p. 851). W[uuml]rtz et al. 
(1996 in Kirk 2003, p. 390) demonstrated that adult parasite 
intensities of greater than 10 adult parasites per eel can reduce the 
proportion of oxygen in the swimbladder of adult eels by approximately 
60 percent when compared to uninfected eels. Simulated swimming 
experiments in European eel indicate the impact of heavily parasitized 
eels (20 or more parasites) results in a decrease in swim efficiency 
and possibly reduced buoyancy. Heavily infected eels were not able to 
swim longer than a few months. Parasites cause the swimbladder to 
shrink, resulting in higher costs of transport (van den Thillart et al. 
2005, p. 105). In addition, heavy infection causes deterioration of the 
swimbladder function due to severe permanent damage.
    According to van den Thillart et al. (2005, pp. 233, 236) a damaged 
swimbladder interferes with the buoyancy control, resulting in poor or 
absent vertical navigation capacity in the open ocean and a decrease in 
swim efficiency which, they hypothesize, prevents the completion of the 
spawning migration. The likely result is death en route to the spawning 
grounds in the Sargasso Sea.
    There is a significant level of speculation about the impact of A. 
crassus on the American eel during outmigration and spawning, neither 
of which can be easily studied under natural conditions. A level of 
uncertainty is therefore, inherent in our analysis. Also unknown is 
whether contaminants may act synergistically with parasites, possibly 
magnifying the impact on the species (USFWS 2006, pp. 7, 26).
    For the American eel, the number of nematodes per infected eel 
(mean intensities) is an important aspect in evaluating the potential 
impact of this nematode on American eel, as is understanding the depths 
at which American eels outmigrate back to the Sargasso Sea, the length 
of that migration, and further understanding of what proportion of the 
American eel completes its life cycle in salt and brackish water where 
infection rates may be significantly lower. Unfortunately much of this 
information is not available.
    Mean intensities in American eels have been found to be 
significantly different among sites, including being significantly 
lower in brackish water when compared to fresh water, (Morrison and 
Secor 2003, p. 1492). The majority of studies of American eels have 
shown fairly moderate levels of intensity of infection. North Carolina 
had a mean ranging from 2.0 to 12.3 nematodes per eel, depending on the 
river (Moser et al. 2001, p. 851). Mean intensities of infection of 
eels from the Hudson River in early studies were 1.0 to 1.7, increasing 
over time to 3.2 and 23.7, depending on the site (Morrison and Secor 
2003, p. 1491). Low to moderate mean intensities of 2.6 to 9.0 were 
reported in the Chesapeake Bay (Barse et al. 2001, p. 1366). It is 
unknown if these relatively moderate mean intensities would have the 
same impact on American eels under natural conditions as was reported 
by the recent laboratory research by van den Thillart et al. (2005, p. 
105) on European eels where higher densities of parasites caused a 
decrease of the optimal swim speed and increased the energetic cost of 
    We remain cautious in extrapolation of these preliminary laboratory 
studies with regard to rangewide implications given the absence of 
evidence for population-level effects, such as reduced recruitment of 
glass eels (which would be an indicator of decreased outmigration 
survival). This being said, we acknowledge the statement by the 
International Council for the Exploration of the Sea (ICES 2001, p. 6) 
that due to the fairly recent invasion of the U.S. by A. crassus and 
the long-lived nature of at least a portion of the American eel 
population, the impact of A. crassus on American eel may not yet have 
been fully realized. ICES (2001, p. 6) concluded that, for the European 
eel, the occurrence of this parasite does not match the timeline for 
when the decline in recruitment for European eel occurred. Given the 
extensive research on the European eel and the reasons for its apparent 
decline this statement should be given due consideration.
    In summary, indigenous parasites are not known to be of significant 
concern to American eel at a population level. During the status 
review, we were provided with new information on the nonindigenous 
parasite A. crassus, including the northern extent of invasion. The 
literature details the impacts to individual European eels by A. 
crassus in a laboratory setting, and puts forward the hypothesis that 
these impacts reduce an individual's chance of successful spawning. 
However, similar research in the American eels has yet to be undertaken 
and several factors pertaining to the American eel may indicate less 
potential impact from A. crassus: (1) The mean intensities reported for 
American eels appear to be moderate; (2) the American eel has a shorter 
outmigration distance to the Sargasso Sea than European eels; (3) some 
areas currently are free from A. crassus infection (Canada, and 
possibly Central and South American and the Caribbean Islands); and (4) 
areas remain where A. crassus is found, that are still

[[Page 4989]]

producing uninfected outmigrating individuals.
    Pathogens. Viruses such as EVA (Eel Virus--America) and bacteria 
are present in the American eel, and periods of stress, such as 
metamorphosis, may activate viruses and bacteria. Although mortality 
from viruses may occur, there is no information available about virus 
prevalence and impact on American eel at a population level.
    Van den Thillart et al. (2005, p. 7) found that European eels 
infected with the rhabdovirus EVEX (Eel Virus European X), a virus 
widely spread in the European eel population, developed hemorrhage and 
anemia during simulated migration in large swim tunnels and died after 
swimming for 1,000 to 1,500 km (estimated European eel outmigration to 
the Sargasso Sea is 5,500 km). The resting group of eels did not 
develop the disease, although they were also infected with the virus. 
This supports the theory that stress, such as completing metamorphosis 
and migrating, may activate the virus. Because none of the infected 
swimming eels survived the swim test, the authors concluded that virus 
infections may adversely affect the spawning migration of eels. The 
virus infection appeared more severe than the infection with the 
swimbladder parasite, A. crassus (van den Thillart et al. 2005, p. 7). 
In a report on the presence of viruses in eel populations from various 
geographic regions and countries, the samples taken from the United 
States (Virginia) and Canada (St. Lawrence River) were negative for 
EVEX virus (van Ginneken et al. 2004, p. 270). Disease screening for 
glass eels used in recent stocking programs have also been free of EVEX 
virus. Other pathogens, such as Aeromonas salmonicida, a bacterium 
known to cause furunculous lesions, exist in cultured American eel 
(Hayasaka and Sullivan 1981, p. 658), but neither rates of infection in 
the wild nor population level impacts have been established.
    In summary, pathogens such as EVEX virus appear to have a 
significant impact on eels in a laboratory setting; however, the 
prevalence of this virus, or any other virus or bacteria, in the 
American eel population is not documented.
Summary of Factor C
    We conclude that predation is not a threat to the American eel at 
the population level, nor are disease and pathogens. We acknowledge 
that there is a high level of uncertainty with regards to the impacts 
on individual silver American eels infested with A. crassus during 
outmigration. However, given the absence of information for population-
level effects, such as reduced recruitment of glass eels, and given 
that there remain uninfected eels for spawning and extensive areas of 
the species range which are not currently invaded by A. crassus or 
infection levels are low to moderate, we have determined that the 
current information does not indicate that A. crassus is a threat to 
the American eel at a population level.
    Because outmigration occurs in the open ocean, direct study of the 
effect of A. crassus under natural conditions will continue to be 
difficult. This emphasizes the need for data collection and analysis 
designed to differentiate between population fluctuations responding to 
natural phenomena, such as oceanic conditions, and those that are 
human-caused. We support the continuation and expansion of the 
coastwide monitoring program started several years ago, and the ongoing 
research being conducted by the scientific community.

Factor D. Inadequacy of Existing Regulatory Mechanisms

    Under this factor we will briefly describe and address whether 
existing regulatory mechanisms are adequate or inadequate to conclude 
that the American eel is not endangered or threatened. As part of our 
analysis of threats under Factors A, B, and E, we describe how certain 
existing regulatory mechanisms directly or indirectly reduce these 
threats (we are unaware of regulatory mechanisms that would directly 
reduce the threats discussed in factor C). Based on this analysis, we 
conclude that Sargassum harvest, freshwater and estuarine benthic 
habitat destruction, streamflow alteration, harvest, passage barriers, 
turbines, and contaminants are not significant threats to the American 
eel at the population level and that additional protection is not 
necessary to determine that listing the species is not warranted. 
Because we found no threat that, individually or in combination with 
other threats, is significant at a population level, there is no 
instance in which the protections provided by existing regulatory 
mechanisms are inadequate such that listing as endangered or threatened 
would be necessary.

Seaweed Harvest

    The status of the American eel with regard to Sargassum harvest is 
influenced by the effect of the following regulation, and therefore, we 
describe in this section how the existing regulatory mechanisms 
directly or indirectly reduces this threat. During the status review, 
we evaluated the harvest restrictions outlined in the second revised 
Fishery Management Plan for Pelagic Sargassum Habitat of the South 
Atlantic Region. The specified maximum and optimum harvest of Sargassum 
severely limit Sargassum harvest, and American eel larvae have not been 
found in the Sargassum. We concluded during the status review that the 
commercial harvest of Sargassum is not a threat to the American eel 
(see Factor A), and therefore we find that the regulations governing 
Sargassum harvest are more than adequate for the protection of American 
eel larvae.

Habitat Degradation

    The status of the American eel with regard to habitat degradation 
is influenced by the effect of the following regulations, and 
therefore, we describe in this section how certain existing regulatory 
mechanisms directly or indirectly reduce this threat.
    Stream Flow and Benthic Habitat. During the status review, we 
evaluated Federal and State and local regulations that afford levels of 
protection and regulate benthic habitat destruction and stream flow 
alteration. The Clean Water Act (33 U.S.C. 1251 et seq.) is the primary 
Federal law, enacted at Federal and State levels that restricts the 
degradation of benthic habitats and flow alteration. The Fish and 
Wildlife Coordination Act, as amended (16 U.S.C. 661 et seq.), has been 
the principal authority for incorporating fish and wildlife 
conservation measures into water development projects. The River and 
Harbors Act of 1938 (Pub. L. 75-685) provided for wildlife conservation 
to be given ``due regard'' in planning Federal water resources 
projects. The Federal Power Act, as amended (16 U.S.C. 791a et seq.), 
contains requirements to incorporate fish and wildlife concerns into 
licensing, relicensing, and exemption procedures. The original Federal 
Power Act provides for cooperation between the Federal Energy 
Regulation Commission (FERC) and other Federal agencies, including 
resource agencies, in licensing and relicensing power projects.
    Many States have specific laws and regulations that limit benthic 
habitat destruction and flow alterations. Some mirror or implement 
Federal clean water law regarding water quality standards, including 
designated uses, criteria, and an antidegradation policy, which can 
provide a sound legal basis for protecting wetland resources, including 
benthic habitats for American eels, through State water quality 
management programs. In most of the

[[Page 4990]]

eastern United States and Canada, the riparian doctrine provides some 
protection for maintenance of instream flows. The riparian doctrine 
generally affords some protection for off-stream uses of water, while 
flow alterations usually must conform to some minimum standard.
    Estuarine habitat. Laws, such as the Estuary Protection Act (16 
U.S.C. 1221 et seq.), the Estuaries and Clean Waters Act of 2000 (33 
U.S.C. 2901 et seq.), and the Coastal Barrier Resources Act (16 U.S.C. 
3501 et seq.), provide financial incentives for estuary habitat 
protection and restoration. Additionally, the Rivers and Harbors and 
the Federal Power Act described above would also address impacts within 
estuarine waters.
    During the status review, we concluded that habitat degradation is 
not a significant threat to the American eel (see Factor A) and 
therefore we find that the regulations governing activities such as 
estuarine and benthic habitat degradation and stream flow alteration 
are adequate for the protection of American eel.


    In general, before the 1960s there were no Federal environmental 
laws regulating pollution. Concerns began to mount with regard to the 
threat of pollution to environmental resources and were first addressed 
in 1965 with the Solid Waste Disposal Act and the Water Resources 
Planning Act. In 1970 the U.S. Environmental Protection Agency (US EPA) 
was established to ``protect human health and safeguard the natural 
environment''. Currently there are numerous International, Federal, and 
State regulations that reduce the threats of contaminants to 
environmental resources such as the American eel. The 1972 Great Lakes 
Water Quality Agreement was signed between the U.S. and Canada to 
``restore and maintain the chemical, physical, and biological integrity 
of the waters of the Great Lakes Basin Ecosystem''. In addition, Canada 
also has authority to manage water resources and control pollution 
under two primary acts, the Ontario Water Resources Act and the 
Environmental Protection Act. Federal regulations that address 
environmental contaminants include the Water Pollution Control Act and 
the Federal Insecticide, Fungicide and Rodenticide Act of 1972, Safe 
Drinking Water Act of 1974, Resource Conservation and Recovery Act of 
1976, Clean Water Act and the Soil and Water Resources Conservation Act 
of 1977, Comprehensive Environmental Response Compensation and 
Liability Act of 1980, and the Oil Pollution Act of 1990. Under the 
Clean Water Act, the U.S. EPA can delegate many of the permitting and 
regulatory aspects of the law to state governments. In accordance with 
the Clean Water Act and state statutory authority, individual states 
have developed water quality regulations that are comparable to and 
often more stringent than the Federal regulations.
    We concluded during the status review that contaminants are not a 
significant threat to the American eel (see Factor E), and therefore we 
find that the regulations governing contaminants are adequate for the 
protection of the American eel.

Fish Passage

    The status of the American eel with regard to barriers and turbines 
are influenced by the effect of the following regulations, and 
therefore, we describe in this section how certain existing regulatory 
mechanisms directly or indirectly reduce these threats.
    During the status review, we evaluated section 18 of the Federal 
Power Act (16 U.S.C. 791a et seq.). Section 18 is the regulatory 
mechanism that specifically provides for fish passage prescriptions by 
the Secretary of Interior (as exercised by the USFWS) and the Secretary 
of Commerce (as exercised by NMFS) for dams regulated by FERC. Most 
States within the range of the American eel in the United States have 
specific fish passage laws, and those State resource agencies often 
work closely with the USFWS or NMFS when creating fish passage 
facilities. Sometimes fish passage is incorporated in the 401 Water 
Quality Certificate issued by the States under the Clean Water Act (33 
U.S.C 1251 et seq.).
    Along the Atlantic coast, most fish passage facilities are 
prescribed under section 18 of the Federal Power Act or recommended 
under section 10(j) of the Federal Power Act administered through FERC 
at hydroelectric facilities. On the mainstem of the upper Mississippi 
River /Illinois Waterway, the Army Corp of Engineers (ACOE) owns and 
operates a series of navigation locks and dams for the Federal 9-Foot 
Channel Project. However, other than recommendations made by resource 
agencies under provisions of the Fish and Wildlife Coordination Act (16 
U.S.C. 661 et seq.), there is no specific regulatory mechanism 
requiring the ACOE to provide fish passage (Wege 2006, p. 6). There may 
be opportunities in the future for fish passage under the proposed 
Federal Navigation and Ecological Sustainability Program, which 
requires Congressional authorization and funding. Many of the large 
reservoirs in the Midwest were constructed by the ACOE and remain under 
its jurisdiction. In the Tennessee River Valley, the Tennessee Valley 
Authority owns and operates 49 developments for flood control, 
navigation, and hydroelectric development; none of these facilities is 
operated specifically for fish passage, although some upstream and 
downstream passage is likely through those mainstem dams with locks 
(Wege 2006, pp. 5-6). Recent records of American eels from the 
Tennessee and Cumberland River are few (Etnier and Starnes 1993, p. 
    Thousands of small dams that were constructed over the last several 
hundred years for water power to run grist mills, saw mills, and 
textile mills, as well as for water storage for drinking water and 
other industrial and municipal purposes, are exempted from most modern 
regulatory mechanisms except for State dam safety codes. Thousands of 
dams in the Mississippi River watershed and along the Atlantic coast 
fall under this category. However, as these structures age, funding is 
often not available to bring them up to State dam safety codes, which 
provides an opportunity for their removal (Wege 2006, p. 5).
    The Energy Policy Act of 2005 (Pub. L. 109-58) amended the Federal 
Power Act amended section 18 of the Federal Power Act and calls for 
administrative hearings when the material facts of an agency-prescribed 
fishway measure can be challenged by the dam owner or other party to 
the proceeding. The alternative fishway measure presented by the dam 
owner or other party can be adopted if it is as effective in purpose 
and economically beneficial to the dam owner. The burden of proof, of 
both the benefit and need for the fish passage, has been somewhat 
shifted from the private sector (i.e., dam owner) to the public sector 
(i.e., agency personnel). Additionally, the agency is now to consider 
the economic impact of a fishway prescription to the dam owner. While 
the process to consider alternative fishways is new, the agencies 
(USFWS and NMFS) have received and considered alternatives from license 
parties as a regular practice, and have revised preliminary conditions 
and prescriptions as new information was received (Hoar 2006, p. 2; DOI 
2005, p. 69808). It is yet to be seen whether these amendments to the 
Federal Power Act will have an effect on eel passage implementation.
    In Canada, there is no licensing or regulatory system comparable to 
FERC for hydroelectric dams. Canadian resource agencies must rely on 

[[Page 4991]]

fisheries laws that can be invoked, and they must often negotiate the 
construction of fishway facilities rather than require them.
    We have concluded that barriers limit, and in some watersheds 
eliminate, access to inland portions of the American eel's range in 
North America, but that there is no indication that the roughly 25 
percent restriction of access to historic freshwater areas is 
significantly impacting the American eel at a population level (see 
Factor A). We have also concluded that turbines can cause regional 
impacts to abundance of American eels within the watershed, but there 
is no evidence that turbines are affecting the species at a population 
level (for full discussion of turbine impacts see Factor E). Therefore 
we find that the regulations governing fish passage are adequate for 
the protection of American eel.

Harvest and Trade

    The status of the American eel with regard to harvest and trade are 
influenced by the effect of the following regulations, and therefore, 
we describe in this section how certain existing regulatory mechanisms 
directly or indirectly reduce these threats.
    During the status review, we reexamined the ASMFC's mechanism for 
regulating the commercial and recreational harvest of American eel 
along the Atlantic coast States (see Factor B. Overutilization) and 
ASMFC's flexibility in responding to changing stock status. The 
American Eel Fisheries Management Plan (FMP) requires that member 
States establish uniform size limits and other regulations for 
commercial harvest. In 2005 and 2006, the ASMFC underwent a public 
process for potential changes to the FMP. In 2006, the ASMFC adopted 
Addendum I to their American Eel FMP (ASMFC 2006c, p. 1; ASMFC 2006d, 
pp. 1-3) which requires a reporting system. Addendum 1 recommends the 
implementation of a specific eel harvester permit or license for each 
State. Under this addendum, each license requires reporting of trip-
level catch and effort, or States can choose to implement an eel dealer 
permit and reporting system. The American Eel Technical Committee under 
the ASMFC stated that this improved monitoring system will assist in 
future stock assessments. The permit or license should be required for 
all eel harvesters, including those who harvest eels for use as bait. 
The American Eel Technical Committee also recommended a specific eel 
report from dealers and a license or permit for dealers, including bait 
dealers. Harvester and dealer reports must differentiate between the 
amount of eels used or sold for food and the amount of eels used or 
sold for bait. The Addendum responds to concerns regarding the lack of 
accurate catch and effort data, and the critical need for these data 
for stock assessment purposes (ASMFC 2006a, p. 2). Although silver eel 
fishery and seasonal closures were options presented during the public 
process (ASMFC 2004b, p. 7), no further harvest restrictions, other 
than those already laid out in the ASMFC's FMP in 2000, have been 
implemented at this time.
    In Canada, harvest restrictions are under the purview of the 
federal government unless the authority has been passed to the 
Provinces. Restrictions and closures are already in effect for certain 
areas in response to the decline in the upper SLR/LO (see Factor B. 
Overutilization). Provincial management programs in Ontario and Quebec 
have imposed license and season restrictions, and reduced quotas, in 
some cases to zero catch (Mathers and Stewart 2005, p. 1). The federal 
government of Canada retains authority within the Maritime Provinces.
    New information was gained on the lack of restrictions in harvest 
from responding countries outside U.S. and Canadian waters, and the 
lack of import restrictions in the responding European countries (see 
Factor B). Our determination, based on the analysis of commercial 
harvest during the status review, is that although abundance of eels is 
likely affected locally and regionally by commercial harvest, 
commercial harvest is not a significant threat to the American eel (see 
Factor B).
    To protect American eel from unregulated recreational harvest, all 
ASMFC member States were required to establish uniform size (6 inches) 
and possession limits (maximum 50 eels per person per day) for 
recreational fisheries, and recreational fishermen are not permitted to 
sell eels without a State license that specifically authorizes this 
activity (ASMFC 2006a, p. 17). During the status review recreational 
harvest was determined not to be a significant threat to the American 
eel at a population level (see Factor B).
    In summary, because we conclude that Sargassum harvest is not a 
threat to the American eel, and habitat degradation, harvest, and fish 
passage, including turbines, were not significant threats to the 
American eel at the population level, it is reasonable to conclude that 
current regulatory mechanisms governing habitat degradation, harvest 
and fish passage, including turbines, are adequate to the extent that 
listing under the Act is not necessary.

Factor E. Other Natural or Manmade Factors Affecting the Species' 
Continued Existence

Hydropower Turbines

    During the status review, we examined the extensive body of 
literature on the impacts of turbines to eels. Specifically, we looked 
at: (1) Types of turbine impacts; (2) variations in mortality and 
injury rates and possible causes; (3) uncertainties and information 
gaps; and, (4) impacts of turbines on the American eel at a population 
    During outmigration, as eels swim downriver, where hydroelectric 
facilities are present, some eels become entrained and enter the 
turbines. Of the eels that enter the turbines, some survive and others 
are injured or die (EPRI 2001, p. 3-1). Smaller turbines and turbines 
that rotate faster pose the greatest threat to eels. The degree of 
injury and mortality increases with larger eels (EPRI 2001, p. 3-8), 
suggesting that mortality rates of large female eels may be 
disproportionately higher than mortality rates of males. Turbine 
mortality to eels has also been shown to be affected by dam size, 
turbine type, load, and specific operating conditions (including 
nighttime versus daytime operation, because eels tend to outmigrate 
during the night; peak versus off peak power production, and level of 
spill), and the behavior of the eels (EPRI 2001, pp. 3-4--3-10; USFWS 
2005b, pp. 30-33). There is only limited data on sublethal effects to 
eels and their impact on outmigration and reproductive viability of the 
population. Sublethal effects include injuries that may result in loss 
of fitness (USFWS 2005b, pp. 34-36), increased risk of predation, and 
delayed migration (as observed in Anguillid species native to New 
Zealand) (Watene et al. 2002 in EPRI 2001, pp. 2-18).
    The Electric Power Research Institute report compiled data on eel 
mortality through turbines and found that not all, but most, eels go 
through turbines due to migration behavior. For eels that go through 
the turbines, the mortality level was highly variable, depending on 
turbine design, size of eels, and operational conditions. For example, 
for survival rates estimated at Moses--Saunders and Beauharnois 
hydropower facilities on the St. Lawrence River, Francis turbines were 
found to result in mortality rates of approximately 15 percent (85 
percent survival), and fixed-blade propeller turbines were found to 
result in mortality rates of

[[Page 4992]]

approximately 25 percent (75 percent survival) (COSEWIC 2006, pp. 45-
46; see EPRI 2001, pp. 3-1--3-11 for more details on the impacts to 
eels from turbines). Higher mortality rates have also been reported. 
Mont[ecirc]n (1985 in McCleave 2001b, p. 593) reviewed literature 
through the early 1970s on injury and mortality on European eel during 
turbine passage. He reported injury rates, where injury likely resulted 
in death, of 40 to 100 percent in 73-cm eels passing through Kaplan 
turbines under various operating conditions. According to Hadderingh 
(1990 in ASMFC 2000, p. 40) and McCleave (2001b, p. 611), if American 
eels have to pass through turbines in their downstream migration, 
mortality rates range from 5 to 60 percent.
    Cumulative mortality refers to the estimated combined mortality 
within a watershed, and is thought to cause significant reductions in 
that watersheds' eel reproductive contribution to the population. 
Verreault and Dumont (2003, p. 247) estimated combined mortality rates 
of 40 percent for Lake Ontario s outmigrating female eels from the 
Moses--Saunders and Beauharnois hydroelectric facilities on the St. 
Lawrence River. The cumulative impact of multiple hydroelectric 
projects within a watershed, as simulated by McCleave (2001b, p. 602), 
indicates substantial decrease in overall eel reproductive contribution 
from a watershed, even when survival rates of eel passage were high 
through each successive turbine or dam project. The simulated 
cumulative mortality within the watershed was approximately 60 percent 
(40 percent survival) of overall reproductive contribution when 
mortality per dam was 20 percent (80 percent survival). McCleave 
states, however, that his model is meant as a tool to compare results 
based on different inputs, not a definitive statement about cumulative 
mortality within the watershed. Based on the data available, we can 
reasonably assume that where American eels encounter one hydropower 
facility during outmigration, there is a typical mortality rate in the 
range of 25 to 50 percent, and when one or more turbines are 
encountered, the range of mortality rate increases to 40 to 60 percent 
for that watershed. This still leaves escapement values (the percent of 
individuals who survive to continue outmigration) of a minimum of 40 
percent and a maximum of 75 percent. Even if the mortality rate has 
been underestimated, there are still eels in freshwater areas that are 
unaffected by turbines, and eels that survive passage in spillover.
    We have updated Busch et al.'s (1998) data on the percentage of 
dams with turbines on the Atlantic coast and have added the Gulf Coast. 
Out of the 33,663 dams, 1,511 (or 4.5 percent) are for hydropower and, 
we assume, are fitted with turbines. Of these only a small percentage 
(2.06 percent) are on terminal dams (Castiglione 2006, p. 1). Terminal 
dams (dams closest to the ocean) fitted with turbines affect American 
eels throughout the watershed as they outmigrate, but dams fitted with 
turbines farther up in the watershed impact only eels outmigrating from 
tributaries and the mainstem of the river above the dam, not 
outmigrating eels from tributaries or mainstem river habitats below the 
dam. Mapping also showed that hydroelectric facilities appear clustered 
in the Northeast and Great Lakes area (Castiglione 2006, p. 2). Still, 
we do not have the percent of eels subject to turbines. This number 
could be relatively small given that: (1) The species' range is 
extensive (see Background, Range); (2) not all Atlantic coast 
watersheds have multiple hydroelectric turbines (USFWS 2005b, p. 31); 
(3) dams that have turbines are likely large dams (more then 50 feet 
high), which often limit upstream passage of eels in these watersheds 
because of their height, and therefore limit the risk of turbine 
mortality or injury at maturity (see Factor A); and, (4) there are 
tributaries to the Gulf of Mexico that have limited impacts from 
hydroelectric turbines, including the Mississippi watershed (which has 
few hydroelectric facilities) (Wege 2006, pp. 5-6).
    The impacts from turbines to the American eel, experts have 
suggested, could result in a decrease in local or regional abundance, 
as well as a population skewed toward smaller and younger females and 
more males, and together these changes in the population could 
ultimately result in a decline in recruitment (USFWS 2005b, p. 34). In 
analyzing the effects of turbines on the American eel, however, we also 
took into account that turbines principally affect freshwater 
inhabitants, leaving the portion of the population that inhabits 
estuarine and marine waters largely unaffected (USFWS 2005b, p. 3). As 
a consequence, a decline resulting specifically from turbine mortality 
may be buffered by the spawning input from eels residing in unaffected 
freshwater habitats, or the estuarine or marine habitats throughout its 
wide range.
    It was also suggested by experts that the importance of turbines as 
a population threat can be assessed only in the context of a general 
understanding of distribution and dispersal patterns of the eel. 
Specifically, a watershed's specific reproductive contribution rates 
and size distribution of females needs to be accounted for in 
determining the impact of turbines on anything larger than a watershed 
level basis (USFWS 2005b, p. 31). Currently there is no such rangewide 
    In lieu of this rangewide estimate, we can look at whether there 
has been an impact to the American eel population, and if so, if it 
relates to the construction of hydropower facilities. As is discussed 
under Population Status, there does not appear to be a rangewide 
decline in recruitment of juvenile eels; therefore, we can draw no 
connection between turbine mortality and population level impacts. 
Additionally, according to Castonguay et al. (1994a, p. 486), the 
timing of the 1980s decline of the American eel in the upper SLR/LO 
does not correlate with the human-caused changes that occurred on the 
St. Lawrence River prior to 1965.
    In summary, turbines, particularly multiple turbines within a 
watershed or turbines on terminal dams, can cause substantial mortality 
within those watersheds. However, turbines are present on a small 
portion of the dams within the Atlantic coast and are absent from most 
of the barriers encountered in the Mississippi Watershed, and there 

remains a percentage of successful eel passage through turbines or with 
spill over the top of dams. Additionally, there is no evidence of a 
population level effect from turbine mortality. We conclude that 
turbines are responsible for decreases in abundance on a local or 
regional scale, but turbine mortality is not a significant threat to 
the American eel at a population level.


    During the status review, we developed a summary of the current 
American eel contaminant literature (Roe 2006, pp. 1-26), and analyzed 
the impacts of: (1) Existing contaminants on the American eel life 
cycle, including levels of uncertainty, and particularly the inability 
to successfully raise eels and consequently study the impacts of 
contaminants on any of the eel life stages; (2) new and emergent 
contaminants; (3) other persistent contaminants, such as genotoxic 
polycyclic aromatic hydrocarbons (PAHs); (4) non-persistent 
contaminants, such as pharmaceutical chemicals and pesticides; (5) 
complex mixtures of contaminants; (6) vitamin deficiency related to 
diet; and (7) combined threats, such as disease,

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parasites, and contaminants, on eel health.
(1) Existing Contaminants
    Concentrations of polychlorinated biphenyls (PCBs), PAHs, 
polychlorinated diphenyldioxins/polychlorinated diphenyl furans (PCDDs/
PCDFs), pesticides such as mirex and di chloro di phenyl tri chloro eth 
ane (DDT), and metals such as mercury were reported in yellow and 
silver American eel tissues from eastern U.S. and Canadian waters. 
However, much uncertainty exists with regard to the population's 
rangewide contaminant load since environmental contaminant data were 
only available from a small portion of the species' range; therefore, 
the contaminant loads within American eel throughout its entire 
population range are unknown.
    The contaminant concentrations reported in American eel tissues are 
within the range of concentrations associated with impacts that have 
been documented in other fish species. These environmental contaminants 
have been shown to have biochemical, immunological, genotoxic 
(chemicals toxic to DNA), growth, survival, and reproductive impacts on 
various fish species. We believe that contaminants therefore have the 
potential to also impact the American eel (Roe 2006, pp. 5-8). 
Interestingly, American eels survive with these contaminant loads at 
concentrations that would be toxic to other fish species. There is, 
however, a potential for the impacts to be fully expressed during 
critical periods of their life cycle such as metamorphosis, hatching, 
and larval development (Robinet and Feunteun 2002, pp. 267, 270-272), 
all of which occur at sea and therefore are currently impossible to 
research under natural conditions (USFWS 2006, p. 24-27). Because of 
this species' unique life history, caution was suggested in utilizing 
surrogate species data in determining impacts of contaminants on eels 
(USFWS 2006, p. 24).
    Inability to successfully study contaminants on all American eel 
life stages. To date, researchers have not been able to successfully 
complete the eel life cycle in the laboratory (Penderson 2003 pp. 324, 
336-337; Palstra et al. 2005, pp. 533-534). Research has also not been 
conducted on the impacts of contaminants on eel embryos and 
leptocephali, or during metamorphosis from the yellow to silver eel 
stage, or during outmigration and reproduction. Two recent laboratory 
studies on the reproductive capacity of European eels by van den 
Thillart et al. (2005, pp. 110, 169) and Palstra et al. (2006, pp. 147-
148) indicated that preliminary studies of PCB and dioxin-like 
contaminant impacts to maturation and fertilization showed negative 
impacts on egg quality and embryonic development. However, artificial 
hormone inducement of maturation in European eels is complicated by 
high female adult mortality rates and high rates of embryo death after 
fertilization (Pedersen 2003, pp. 336-337; Knights submitted, pp. 1-2). 
Therefore, it is difficult to be certain whether the mortality rates 
are associated with artificial maturation or fertilization techniques 
or with exposure to contaminants (Knights submitted, p. 2). Unless or 
until the issue of embryo death can be attributed exclusively to the 
presence of contaminants, the data is still inconclusive with regard to 
the determination of the impacts of PCB and dioxin-like contaminants at 
a population level in the American eel.
(2) New and Emergent Contaminants
    The impacts of new and emergent chemical contaminants in fish are 
unclear and not available for the American eel. An example of new and 
emergent contaminants presented during the workshop (USFWS 2006) was 
polybrominated diphenyl ethers (PBDEs), a group of chemicals used as 
flame retardants in a multitude of consumer products (Agency for Toxic 
Substances and Disease Registry or ATSDR 2004, pp. 11-12). PBDEs are 
similar to PCBs in that they are lipophilic, persistent in the 
environment, and bioaccumulate in organisms. However, the impacts to 
fish and other aquatic organisms have not been completely defined in 
the scientific literature. There is evidence that PBDEs cause enzyme 
activity alterations and delayed embryonic hatching in fish, and they 
result in behavioral alterations (Timme-Laragy et al. 2006, pp. 1098-
1103). Concentrations of PBDEs have been measured in European eels (de 
Boer 1990, pp. 315-318; Covaci et al. 2004, pp. 3851-3855) and in other 
species (Lebeuf et al. 2004, pp. 2973-2976); however, the impacts of 
PBDEs to eels were not discussed. Therefore any impacts to the American 
eel at a population level would be purely speculative.
(3) Impacts of Genotoxic Contaminants
    The impacts of genotoxic PAHs on the eel remain uncertain. There is 
considerable evidence that indicates a causal relationship between 
exposure to PAHs and genotoxic impacts such as tumor frequency, 
deformities, and other lesions in fish, particularly bottom feeding 
fish (Black 1983, pp. 328-333; Metcalfe et al. 1990, pp. 133-139; 
Baumann and Harshbarger 1995, pp. 168-170; Baumann et al. 1996, pp. 
131-149; Johnson et al. 1998, pp. 125-134). Couillard et al. (1997, pp. 
1918-1926) documented the occurrence of precancerous lesions in liver 
tissues from migrating American eels from the St. Lawrence River. The 
prevalence of the lesions in the eel liver tissue was reported to be 
correlated with increasing contamination in eels, and the authors 
concluded that PAHs may have been the cause (Couillard et al. 1997, p. 
1924). Recent research in American eels (Schlezinger and Stegeman 2000, 
pp. 378-384) and European eels (Doyotte et al. 2001, pp 1317-1320; 
Bonacci et al. 2003, pp. 470-472; Mariottini et al. 2003, pp. 94-97) 
has shown that induction of enzyme activity has also been used as a 
biomarker for exposure to PAHs and similar contaminants. Genotoxic PAHs 
may be impacting successful outmigration, but impacts of lesions and 
tumors have not been researched under natural conditions or within the 
(4) Non-Persistent Contaminants
    Short-term exposure to non-persistent contaminants during critical 
American eel life stages may be of concern (USFWS 2006, p. 25), but 
uncertainty remains. The literature has shown that endocrine disrupting 
environmental contaminants such as 4-nonylphenol (which is formed 
during the industrial synthesis of detergents), and pesticides such as 
atrazine and diazinon, cause physiological changes, inhibit growth, and 
therefore inhibit the survival of wild Atlantic salmon (Salmo salar) 
along the Canadian Atlantic coast (Moore and Waring 1996, p. 758; 
Fairchild et al. 1999, p. 349; Brown and Fairchild 2003, p. 146; 
Arsenault et al. 2004, p. 255; Waring and Moore 2004, p. 93). American 
eels are sporadically exposed to relatively high concentrations of non-
persistent contaminants during their migration through the St. Lawrence 
River to the Sargasso Sea (Pham et al. 2000, p. 78). For example, the 
largest primary physio-chemical municipal sewage treatment plant in 
North America is located in Montreal, and treated effluent is 
discharged to the St. Lawrence River (Environment Canada 2006, pp. 1-3; 
USFWS 2006, p. 25). At this location, there is evidence of endocrine 
disruption in other aquatic organisms exposed to the effluent from 50 
km upstream to 50 km downstream of the plant (Aravindakshan et al. 
2004, pp. 156-164; Gagn[eacute] et al. 2004, pp. 33-43).

[[Page 4994]]

However, currently there is no information within the literature on the 
sensitivity of eels to short-term exposure to these potentially 
endocrine disrupting non-persistent contaminants.
(5) Exposure to Complex Mixtures of Contaminants
    The cumulative impacts of complex mixtures of contaminants on eel 
species are unknown. Fish and other wildlife are not exposed to just 
one single contaminant in the aquatic environment. Contaminants mixed 
together may interact and have additive (Dioxin-like contaminants: Safe 
1990, pp. 71-73; Van den Berg et al. 1998, pp. 775-776) or synergistic 
(PAHs: Wassenberg and Di Giulio 2004, p. 1662) effects.
(6) Vitamin Deficiency Related To Diet
    In addition to contaminant-induced impacts discussed above, 
decreased concentrations of antioxidant vitamins may also be impacting 
American eel survival, but this remains uncertain. Deficiences of 
antioxidant vitamins, such as thiamine, vitamin B1, and astaxanthin (a 
precursor to vitamin A), have been associated with increased early 
mortality in salmon and trout species (Fitzsimons 1995a, p. 267; 
Fitzsimons 1995b, pp. 286-288; Vuorinen et al. 1997, pp. 1151-1163; 
Fitzsimons et al. 2001, p. 229). It has been suggested that the 
occurrence of the early mortality syndrome in Lake Ontario lake trout 
is related to alewife (Alosa pseudoharengus) and their high thiaminase 
content (Fitzsimons 1995b, p. 288). Thiaminase are a group of enzymes 
that break down thiamine in the body and Alewife is a common food item 
for young trout. Because alewife are also consumed by American eels it 
has been hypothesized that American eels in Lake Ontario may be 
experiencing effects from reduced levels of thiamine. However, because 
this hypothesis has yet to be tested this theory remains speculative.
(7) Impacts of Combined Threats
    Finally, contaminants can impact the immune system and therefore 
increase the organism's susceptibility to other threats such as 
diseases, parasites, and bacterial and viral infections (Arkoosh et al. 
1996, pp. 1154-1161, Arkoosh et al. 1998, p. 182; Grassman et al. 1996, 
p. 829; Couillard et al. 1997, p. 1916; Johnson et al. 1998, p. 125; 
Van Loveren et al. 2000, p. 319; Zelikoff et al. 2000, p. 325), but the 
effect on the American eel remains uncertain. The cumulative stress of 
the complex mixtures of environmental contaminants and other threats 
may potentially lead to increased mortality. Field studies have 
documented susceptibility to infections in European and North American 
fish species (Arkoosh et al. 1998, pp. 188-189; Van Loveren et al. 
2000, pp. 322-323; Zelikoff et al. 2000, pp. 325-330), which would make 
these fish more susceptible to disease. Bacterial pathogens have been 
isolated in American eels, and the authors suggested that increased 
prevalence of these pathogens may potentially be related to stress and 
subsequent decreased immune resistance (Hayasaka and Sullivan 1981, p. 
658; Davis and Hayasaka 1983, pp. 559, 561; see Factor C).
    In summary, contaminants may impact early life stages of the 
American eel, but we remain cautious in extrapolation of these 
preliminary laboratory studies with regard to rangewide implications 
without specific information. A correlation between the contamination 
of the upper SLR/LO and the timing of the 1980s decline of American eel 
in the upper SLR/LO is not evident (Castonguay et al. 1994a, pp. 482-
483), and current environmental laws and regulations have significantly 
decreased the discharge of many persistent environmental contaminants. 
Given the absence of evidence for population-level effects, such as 
reduced recruitment of glass eels (which would be an indicator of 
decreased outmigration survival, or egg or leptochephali survival as a 
result of the impacts of contamination), we believe that the available 
information on contaminants does not indicate a significant threat to 
the American eel at a population level.
    Because spawning and egg and leptochephali maturation occurs in the 
open ocean, directly study of the effects of contaminants under natural 
conditions will continue to be difficult. This emphasizes the need for 
data collection and analysis designed to differentiate between 
population fluctuations responding to natural phenomena such as oceanic 
conditions and those that are human-caused. We support the continuation 
and expansion of the coastwide monitoring program started several years 
ago, and the ongoing research being conducted by the scientific 

Oceanic Conditions

    During the status review, we explored the relationship between 
oceanic conditions and the recruitment of leptocephali to coastal and 
riverine habitats both hypothetically and through correlative data. 
Additionally, we investigated and describe briefly here the types of 
oceanic conditions that have the potential to impact American eels. 
Finally, we analyzed the potential for oceanic conditions to impact the 
American eel at a population level.
    Variations in oceanic conditions have been linked to wide-ranging 
and long-term changes in many fish, invertebrate, and zooplankton 
species. General ecological responses to oceanic variations encompass 
changes in timing of reproduction, egg viability, timing of food 
availability, larval growth and mortality, population sizes, spatial 
distribution, and inter-specific relationships (such as competition and 
predator-prey relationships), by affecting temperature, salinity, 
vertical mixing, circulation patterns, and ice formation. However, the 
relationships are complex, usually non-linear, and operate through 
complex mechanisms through several trophic levels over the ecosystem, 
and over a broad range of time and spatial scales (Colbourne 2004, p. 
16). Further, a population's response is likely to vary in different 
regions (Ottersen et al. 2001, pp. 1-14; Attrill and Power 2002, pp. 
275-278; Hurrell et al. preprint, p. 10, 22-25, 38; Perry et al. 2005, 
p. 1-4; Weijerman et al. 2005 abstract and appendix 2, p. 3).
    Oceanic conditions likely play a significant role in the population 
dynamics of American eel (Knights et al. 2006, p. 2), but the 
relationships between specific oceanic conditions and eel recruitment 
remain almost entirely hypothetical. Changes in oceanic conditions have 
previously been thought not to be correlated with the decline in the 
upper SLR/LO (Castonguay et al. 1994b, p. 6; ICES 2001, p. 5). To 
better understand this complex relationship given the scant available 
literature, we requested assistance from oceanic and eel experts. Part 
of the assistance was a summary of all available literature, entitled 
American Eel Leptocephali-Larval Ecology and Possible Vulnerability to 
Changes in Oceanographic Conditions, by M. Miller of the Ocean Research 
Institute at the University of Tokyo (cited as Miller 2005). 
Additionally, we examined published and unpublished data on the topic 
(Knights, Friedland, Casselman, Miller, Kritzer, and Govoni in USFWS 
2005b, pp. 50-65).
    The types of oceanic conditions that have the potential to affect 
eels in the North Atlantic include: (1) Changes to sea surface 
temperatures (SSTs); (2) changes to mixed layer depth (MLD); (3) 
deflections of the Gulf Stream at the Charleston Bump and Cape 
Hatteras; and (4) other changes. Changes of SSTs include inhibition of 
spring mixing, and nutrient recirculation and productivity, which may 
influence leptocephali food

[[Page 4995]]

abundance. MLD (the depth to which mixing is complete, relative to the 
layer of ocean water beneath it) changes include changes in size and 
depth of leptocephali habitat, which would affect leptocephali 
abundance, survival, or transport. Changes in the Gulf Stream could 
interrupt migration by slowing or removing leptocephali from the Gulf 
Stream, and any transport and subsequent recruitment problems might be 
accentuated at the extremes of the species' range. The ``other'' 
category included changes to other aspects of the Gulf Stream, such as 
the formation of eddies, which may spin leptocephali off of the main 
current (USFWS 2005b, p. 53).
    Variation in oceanic conditions is often depicted by the North 
Atlantic Oscillation Index (NAOI). The NAOI is a measure of oceanic-
climate changes, expressed as the difference in atmospheric pressure 
measured between Greenland and the Azores. The NAOI has phases 
(positive and negative) that have important oceanographic effects. For 
example, a positive (high) NAOI is indicated by periods of stronger 
winds, greater surface-water mixing, reduction of the Gulf Stream, 
shift of the Gulf Stream in a northeast direction, and increases in 
deep water formation and water mass formation in the Labrador Sea (and, 
it is hypothesized, weak eel recruitment); a negative NAOI shifts the 
Gulf Stream south and increases the transport in the Labrador Current 
(the western boundary current of the North Atlantic subpolar gyre) (and 
it is hypothesized, a strong eel recruitment). These oscillations 
correlate with other oceanic factors such as MLD, SST anomalies, and 
position of the North Wall (a steep water temperature gradient) of the 
Gulf Stream (for further discussion of NAOI see Weijerman et al. 
Appendix 2, pp. 3, 9).
    The NAOI has received considerable attention because of its strong 
negative correlation with recruitment of European eels (glass eels 
recruited to den Oever, Netherlands) (ICES 2001, p. 5) and a similar, 
but weaker, negative correlation with recruitment of American eels 
(juvenile eels recruited to the St. Lawrence River) (ICES 2001, p. 5; 
Cairns et al. 2005, Table 9.2, p. 66). From the mid 1950s to 1978/1979 
winter the NAOI was in a 24 year negative phase. From 1979/1980 winter 
to 1994/1995 winter the NAOI was in a positive phase (Weijerman et al. 
Appendix 2, pp. 3, 9) and this positive phase may have continued until 
recently. During this prolonged positive (high) phase European eel 
recruitment had been correspondingly low (ICES 2002, p. 2). The last 
few winters, however, have not been strongly positive (Hurrell et al. 
preprint, p. 4), which may indicate that the NAOI is beginning to shift 
to a negative phase, which would benefit eels (USFWS 2005b, p. 66). A 
shift to a negative phase would be consistent with the observation that 
the NAOI seems to follow 7- to 8-year cycles, superimposed on 20- to 
30-year cycles (Knights 2003, p. 238).
    The correlation between NAOI and recruitment suggests that oceanic 
conditions are currently the most influential variable affecting 
recruitment. As noted earlier, efforts to model the population dynamics 
of American eel are inherently limited by sparse or nonexistent data. 
Nonetheless, sensitivity analysis of one modeling effort indicated that 
oceanic conditions had greater eel population effects than fishing, 
dams, or other habitat impacts (BEAK 2001, pp. 5.10-5.11).
    In summary, oceanic conditions influence growth, recruitment, and 
distribution of many marine species. The interactions between the 
marine environment and production of marine species, however, are 
exceedingly complex. Although the interactions are not completely 
understood, the success of early eel life stages and subsequent 
recruitment to fresh water is dependant on oceanic conditions, which 
are subject to natural variation. Natural conditions can, when a 
species is significantly reduced in range or abundance, be considered a 
threat. However, there is no indication that the American eel is 
suffering this level of reduction in either abundance or range. 
Therefore, because oceanic conditions are within normal variations, the 
American eel is evolutionarily adapted to oceanic variations, and there 
is no indication that the American eel is at a reduced level where this 
natural oceanic variation would significantly affect the species, we 
have concluded that oceanic conditions are not now, and there is no 
information indicating oceanic conditions should be in the future, a 
significant threat to the American eel at a population level.
Summary of Factor E
    In conclusion, hydropower turbines are a source of ongoing 
mortality. This mortality has affected, and will continue to affect, 
regional presence and abundance of eels. However, the current 
information does not provide evidence to support turbines as a 
significant threat to the American eel at a population level. There is 
substantial uncertainty on the effects of contaminants on the American 
eel and more research is needed. However, after examination, the 
literature does not support a population level impact from 
contaminants. Oceanic conditions are highly variable and cyclical. They 
determine recruitment to the continent, and therefore they have a 
substantial influence on the presence and abundance of eels on the 
continent, particularly in freshwater habitats. Oceanic conditions are 
a naturally occurring influence on the American eel during its early 
life history, and are not a significant threat to the American eel. In 
sum, given the absence of evidence for population-level effects, such 
as reduced recruitment of glass eels, we have concluded that there is 
not supporting data to indicate other natural or manmade factors as a 
significant threat to the American eel.


    The Act defines the term ``threatened species'' as any species (or 
subspecies or, for vertebrates, distinct population segment) that is 
likely to become an endangered species within the foreseeable future 
throughout all or a significant portion of its range. The term 
``endangered species'' is defined as any species that is in danger of 
extinction throughout all or a significant portion of its range. The 
principal considerations in the determination of whether a species does 
or does not warrant listing as a threatened or endangered species under 
the Act are the threats that confront the species, as discussed in the 
five factor analysis above.
    In reviewing the status of the American eel, we make the following 
findings. The species has been extirpated from some portions of its 
historical freshwater habitat over the last 100 years or so, mostly as 
a result of dams built by the late 1960s. There is also evidence that 
the species' abundance within freshwater habitats, and to some degree 
estuarine habitats, has declined in some areas (e.g., upper SLR/LO and 
the Chesapeake Bay) likely as a result of harvest or turbine mortality, 
or a combination of factors. However, the species remains widely 
distributed over the majority of its historical range. Based on 
information from the ASMFC stock assessment and peer review and the 
COSEWIC Assessment and Status Report, an indication of decline exists 
in yellow eel abundance, but recent glass eel recruitment trends, 
although variable from year to year, appear stable over the past 15 
years. The American eel is a highly resilient species, with the ability 
to occupy the broadest range of habitats within freshwater, as well as 
estuarine and marine waters, and it remains a widely distributed fish 
species. The lack

[[Page 4996]]

of population subdivision (i.e., panmixia) in the American eel provides 
resilience to genetic problems that can result from decline and 
isolation of subpopulations.
    Although roughly 25 percent of the American eel's historical 
freshwater habitat is now inaccessible due to dams, the loss of this 
habitat does not threaten the species' long-term persistence. This is 
because a large amount of freshwater habitat still remains (roughly 75 
percent of historic freshwater habitat in the United States remains 
available and occupied by the American eel), from which both males and 
females outmigrate, and because a portion of American eels complete 
their life cycle in estuarine and marine waters without entry into 
freshwater. Although the significance of the estuarine and marine eel 
contribution to reproduction is considered speculative by some, a 
growing number of researchers think the contribution could be 
substantial (Tsukamoto and Arai 2001, p. 275; Jessop 2002, p. 228; 
Kotake et al. 2005, p. 220; Cairns 2006a, p. 1; Knights et al. 2006, 
pp. 12-13), and there is no doubt that substantial amounts of estuarine 
and marine waters remain available to and are occupied by the American 
eel throughout its range.
    The threat of Sargassum harvest is no longer considered a threat 
due to new information indicating that the American eel larvae do not 
utilize Sargassum, and due to regulations restricting its harvest. 
Recreational and commercial eel harvests are no longer factors of 
concern at a population level due to economics, the species' 
resilience, and existing regulatory mechanisms. Although mortality 
during outmigration due to parasites and contaminants, and the 
potential effects of contaminants on early life stages, remain a 
concern, we have no information indicating that these threats are 
currently causing or are likely to cause population level effects to 
the American eel. We have no information indicating that predation or 
competition with nonnatives or mortality from turbines are causing 
population-level effects. Recruitment success of the American eel is 
dependent on ocean conditions, and variation in ocean conditions causes 
fluctuation in recruitment. However, because the available information 
indicates that the species remains widely distributed and glass eel 
recruitment trends appear stable over the past 15 years, observed ocean 
conditions do not threaten the current population status of the 
American eel. Also, we have no information to indicate that ocean 
conditions are likely to threaten the American eel at a population 
level in the future.
    In reviewing the status of the American eel, we also considered 
whether there was any area where the species is threatened or 
endangered throughout a significant portion of its range. We considered 
threats to its spawning, migratory, and growth habitats (see discussion 
under Factor A and Ocean Conditions in Factor E) and found no area 
where the species is threatened or endangered throughout a significant 
portion of its range. The Sargasso Sea, where the American eel spawns, 
is for that reason a significant portion of the range, but we 
identified no threats to this habitat. Similarly, the open ocean 
migratory habitat of the American eel is also a significant portion of 
the range, but we identified no threats to this habitat either.
    The American eel's growth habitat consists of those areas, apart 
from its spawning and migratory habitats, where the species' growth 
primarily takes place. We evaluated whether the upper SLR/LO, an area 
of the American eel's growth habitat that has experienced an extreme 
decline in American eel abundance, is a significant portion of the 
range. The American eel is panmictic, genetically homogeneous, and 
capable of occupying a diversity of growth habitats. It currently 
occupies a number of growth habitats, each of which is similar in 
habitat characteristics. Therefore no one growth habitat would be a 
significant portion of the range unless it was significant in terms of 
eel reproductive contribution. Although it has been suggested that the 
upper SLR/LO historically contributed a disproportionately larger 
amount of reproduction than other freshwater areas of similar size, 
significant uncertainties have been identified regarding this analysis 
(COSEWIC 2006, pp. 35-41). Even if the upper SLR/LO had historically 
contributed a disproportionately larger amount of reproduction than 
other freshwater areas of similar size (see Population Status in 
Background section), our consideration of the data on facultative 
catadromy (the ability to grow and become sexually mature in estuarine 
and marine waters in addition to freshwater) suggests that the total 
reproductive contribution from the rest of the range (including other 
freshwater and all estuarine and marine waters) outside the upper SLR/
LO is substantially greater than the historical reproductive 
contribution from the upper SLR/LO (see Population Status in Background 
section). Consequently, any historical additional reproductive 
contribution from the upper SLR/LO does not make this area 
significantly more important than if its historical reproductive 
contribution was similar to that of other similarly sized areas within 
the range of the species. Because the upper SLR/LO area does not 
contain any unique or particularly high-quality habitat, does not 
contribute to any genetic differences, contains substantially less than 
50 percent of the growth habitat for the eel, and does not appear to 
contribute greatly to the long-term persistence of the species, we have 
determined that it is not a significant portion of the range. In 
addition, even if the SLR/LO were to be considered a significant 
portion of the range we find from the record before us that the eel is 
not threatened or endangered in the SLR/LO because eels will likely 
persist there into the foreseeable future (for discussion of this 
``rescue effect'' see Background, Population Status). The American eel 
is panmictic and substantial reproductive contribution comes from 
outside the upper SLR/LO. We believe that the upper SLR/LO will likely 
continue to receive eels and, therefore, extirpation of eels from the 
upper SLR/LO is unlikely.
    In addition, we considered whether there are any segments of the 
population of American eel that would qualify as distinct population 
segments (DPSs) under the USFWS's Policy Regarding the Recognition of 
Distinct Vertebrate Population Segments Under the Endangered Species 
Act (DPS Policy) (USFWS 1996). To be identified as a DPS, a population 
must satisfy both the discreteness and significance tests of the DPS 
Policy. Because the species is panmictic (a single inter-breeding 
population), no part of the species' population meets the discreteness 
test of the DPS policy. Because no discrete populations can be 
identified, there are no populations for which we could evaluate 
significance. Therefore, no American eel DPSs can be recognized.
    Due to the concerns about the status of the American eel in Canada, 
we considered delineation of a Canadian DPS using the international 
border. However, we determined that the Canadian population of American 
eels would not satisfy the significance test. There is no evidence to 
suggest that eels in Canada are genetically different from eels in 
other parts of the species' range, that eels in Canada inhabit a unique 
ecological setting, that loss of eels in Canada would result in a 
significant gap in the range of the species, or that the Canada 
population of eels otherwise could be considered significant under the 
DPS policy. Also, because the species is panmictic and juveniles are 
distributed randomly over a wide range,

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and because substantial reproductive contribution occurs over most of 
the range, Canada will likely continue to receive eels despite any 
reduction in yellow eel abundance in Canada. Therefore, the Canadian 
population would not be considered endangered or threatened and as a 
result would not qualify as a DPS under the DPS policy.
    In summary, we find that the American eel remains widely 
distributed over their vast range including most of their historic 
freshwater habitat, eels are not solely dependent on freshwater habitat 
to complete their lifecycle utilizing marine and estuarine habitats as 
well, they remain in the millions, that recruitment trends appear 
variable but stable, and that threats acting individually or in 
combination do not threaten the species at a population level. On the 
basis of the best available scientific and commercial information, we 
conclude that the American eel is not likely to become an endangered 
species within the foreseeable future throughout all or a significant 
portion of its range and is not in danger of extinction throughout all 
or a significant portion of its range. Therefore, listing of the 
American eel as threatened or endangered under the Act is not 


    The primary author of this finding is Heather Bell, Fisheries 
Biologist, Region 5, USFWS, 300 Westgate Center Drive, Hadley, 
Massachusetts, 01035.

References Cited

    A complete list of all references cited is available on request 
from the U.S. Fish and Wildlife Service's Region 5 Regional Office (see 
ADDRESSES section above).

    Authority: The authority for this action is the Endangered 
Species Act of 1973, as amended (16 U.S.C. 1531 et seq.).

    Dated: January 23, 2007.
Kevin Adams,
Acting Director, U.S. Fish and Wildlife Service.
[FR Doc. 07-429 Filed 2-1-07; 8:45 am]