[Federal Register: November 2, 2001 (Volume 66, Number 213)]
[Page 55693-55697]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]



Fish and Wildlife Service

Marine Mammals; Finding on Petition To List the Alaska Stock of 
Sea Otters as Depleted

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Finding on petition.


SUMMARY: On August 21, 2001, the U.S. Fish and Wildlife Service (FWS) 
received a petition under section 115 of the Marine Mammal Protection 
Act (MMPA) from the Center for Biological Diversity. The petition 
requests that FWS list the Alaska stock of sea otters as depleted. The 
FWS finds that the petition does not present substantial information 
that the petitioned action is warranted. The FWS has determined that 
the statewide population of sea otters in Alaska is larger than 
presented in the petition. Furthermore, the best available scientific 
information indicates that multiple stocks of sea otters exist in 

FOR FURTHER INFORMATION CONTACT: Douglas Burn, Wildlife Biologist, 
Marine Mammals Management Office, 1011 East Tudor Road, Anchorage, 
Alaska 99503, or telephone 907/786-3800 or facsimile 907/786-3816.



    The sea otter, Enhydra lutris, is the smallest species of marine 
mammal. Sea otters occur primarily in shallow, nearshore marine 
habitats (Rotterman and Simon-Jackson 1988). They eat a wide variety of 
benthic (i.e., bottom dwelling) invertebrates, including bivalves, 
molluscs, gastropods, crustaceans, echinoderms, and occasionally 
octopus and fish. This dependence on nearshore benthic invertebrates 
greatly influences sea otter distribution, and as a result, they are 
seldom found in deep water. Sea otters seem to prefer areas with kelp 
beds, but this is not an essential habitat requirement (Riedman and 
Estes 1990). Although predominantly marine, they will occasionally haul 
our on shore to rest.
    Taxonomically, three subspecies of sea otter have been identified 
(Wilson et al. 1991). The northern sea otter contains two subspecies: 
Enhydra lutris kenyoni, which occurs from the Aleutian Islands to 
Oregon, and Enhydra lutris lutris, which occurs in the Kuril Islands, 
Kamchatka Peninsula, and Commander Islands in Russia. The third 
subspecies, Enhydra lutris nereis, occurs in California and is known as 
the southern sea otter.
    Historically, sea otters occurred around the North Pacific rim from 
Hokkaido, Japan, through the Kuril Islands, Kamchatka Peninsula, the 
Commander Islands, the Aleutian Islands, peninsular and south coastal 
Alaska, and southward to Baja California (Kenyon 1969). Extensive 
commercial hunting of sea otters began following the arrival in Alaska 
of Russian explores in 1741 and continued during the 18th and 19th 
centuries. By the time sea otters were afforded protection from 
commercial harvests by international treaty in 1911, the species was 
nearly extinct throughout its range, and may have numbered only 1,000-
2,000 individuals (Kenyon 1969).
    The remaining sea otters were distributed as 13 isolated remnant 
populations scattered throughout the historic range. Once commercial 
harvests ceased, 11 of the 13 remaining

[[Page 55694]]

populations began to grow and recolonize their former range. By the 
early 1960s, sea otters had not yet returned to southeast Alaska. In 
the mid-1960s, the Alaska Department of Fish and Game translocated sea 
otters from Amchitka Island in the Aleutians and Prince William Sound 
to several sites throughout southeast Alaska. Similar to the remnant 
populations, these translocated populations began to grow and expand 
their geographic range. By the mid-1980s, sea otters had recolonized 
much of their pre-exploitation range.
    In April 1992, FWS conducted an aerial survey of sea otters 
throughout the entire Aleutian archipelago (Evans et al. 1997). The 
most striking results of this survey were that sea otter density and 
abundance in the Rat, Delarof, and western Andreanof Islands had 
unexpectedly declined by more than 50% since 1965. Boat-based surveys 
of sea otters at several islands in the Near, Rat, and Andreanof 
Islands further documented an ongoing decline of sea otters during the 
1990s (Estes et al. 1998).
    In April 2000, the FWS Marine Mammals Management Office replicated 
the 1992 aerial survey in the Aleutians. Overall, sea otters in the 
Aleutian Islands have declined by 70% during the 8-year period from 
1992 to 2000 (U.S. Fish and Wildlife Service, unpublished data). The 
largest declines occurred in the Rat Islands (87%) and the central 
Aleutians (71%).
    Based on the results of this survey, on August 22, 2000, FWS 
designated sea otters in the Aleutians (from Unimak Pass to Attu) as a 
candidate species under the Endangered Species Act (ESA) (65 FR 67343). 
On October 25, 2000, FWS received a petition from the Center for 
Biological Diversity (CBD) to list sea otters in the Aleutians as 
threatened or endangered under the ESA. Due to a backlog of court-
ordered listing and critical habitat designations, funds were not 
available to prepare a proposed rule in Fiscal Year (FY) 2001.
    Immediately following the completion of the Aleutian sea otter 
survey, in May 2000 the FWS conducted an aerial survey of sea otters on 
the north side of the Alaska Peninsula from False Pass to Cape 
Seniavin. The FWS also conducted aerial surveys along the south side of 
the Alaska Peninsula in April 2001. The results of these surveys, which 
replicated a baseline study conducted in 1986 (Brueggeman et al. 1988), 
indicate that the sea otter population has also declined in these 
areas. In June 2001, the FWS conducted an aerial survey of the Kodiak 
Archipelago for comparison with data collected in 1994. A comparison of 
the two surveys, which used the same aircraft, pilot, and observer, 
indicate the sea otter population has declined in the Kodiak area as 
well. Based on the results of surveys conducted in the past year, the 
Alaska Region of the FWS has requested funding in FY2002 to prepare a 
proposed rule to list sea otters in southwest Alaska under the ESA.
    On August 21, 2001, FWS received a petition from CBD to list sea 
otters throughout their range in Alaska as depleted under the MMPA 
(September 6, 2001, 66 FR 46651). Section 115(a)(3)(B) of the MMPA 
requires the FWS to publish a finding in the Federal Register as to 
whether the petition presents substantial information indicating that 
the petitioned action may be warranted.

Identification of Sea Otter Stocks in Alaska

    Findings of depleted status must be made on the species or 
population stock level. Amendments to the MMPA in 1994 included section 
117 (16 U.S.C. 1386), which mandated preparation of stock assessments 
for each marine mammal stock that occurs in waters under the 
jurisdiction of the United States. In 1995, FWS published a final stock 
assessment for the northern sea otter in Alaska as a single stock (60 
FR 52008). Section 117(c) requires that stock assessments be reviewed: 
(A) At least annually for stocks which are specified as strategic 
stocks; (B) at least annually for stocks for which significant new 
information is available; and (C) at least once every 3 years for all 
other stocks. If the review indicates that the status of the stock has 
changed or can be more accurately determined, the stock assessment 
shall be revised according to the process outlined in section 117(b). 
The first revision to the stock assessment occurred in 1998.
    In February 1998, FWS published a draft revision of the northern 
sea otter stock assessment that identified three stocks of sea otters 
in Alaska (63 FR 10936). The revision identified a southeast Alaska 
stock (Cape Yakataga to Dixon Entrance), a southcentral Alaska stock 
(Cook Inlet to Cape Yakataga), and a southwest Alaska stock (Cook Inlet 
to Attu Island, including the Kodiak archipelago).
    In August 1998 the Alaska Sea Otter Commission (ASOC) requested a 
proceeding on the record as outlined in section 117(b)(2) of the MMPA 
to contest the identification of multiple stocks of sea otters in 
Alaska. After considerable discussion, FWS and ASOC signed a Memorandum 
of Agreement (MOA) in July 1999 to further investigate the issue of 
stock structure of sea otters in Alaska. On August 12, 1999, the ASOC 
(now the Alaska Sea Otter and Steller Sea Lion Commission) withdrew the 
request for a formal proceeding on the record. A revised stock 
assessment for the northern sea otter in Alaska has not been finalized.
    The identification of multiple stocks of sea otters in Alaska in 
our 1998 draft revision was based on an analysis of existing data on 
distribution, population response, phenotypic data, and genotypic data 
according to Dizon et al. (1992). One element of the MOA concerned 
scientific peer review of the analysis that identified multiple stocks 
of sea otters in Alaska. That element has been satisfied by the 
publication of Gorbics and Bodkin (2001), who applied the criteria of 
Dizon et al. (1992) and identified three stocks of sea otters in 
Alaska: Southwest, southcentral, and southeast. Another element of the 
MOA involved the completion of additional genetics analysis using both 
mitochondrial and nuclear DNA, as well as a larger sample size. This 
study is complete and a manuscript is in preparation for scientific 
peer review and publication (Cronin et al. in prep.). The results of 
this study also support the identification of multiple stocks of sea 
otters in Alaska.
    The FWS is currently in the process of revising our original 1995 
stock assessment for northern sea otters in Alaska. Based on the best 
available scientific evidence, FWS anticipates publishing draft stock 
assessments identifying multiple stocks of sea otters in Alaska. The 
drafts soon will be available for public review and comment.

Current Population Size

    The Petition presents an estimated statewide sea otter population 
of fewer than 38,000 individuals. This figure was calculated using 
population estimates from the 1998 draft stock assessments, along with 
the estimated abundance for the Aleutians presented in the Candidate 
Species announcements (65 FR 67343). The statewide population estimate 
presented in the petition is inaccurate for several reasons. First, 
available population estimates are omitted from substantial portions of 
the State, including the Alaska Peninsula and Kodiak archipelago. 
Second, the estimate used for the Aleutian Islands is incorrect. 
Further analysis of the Aleutian aerial survey data has resulted in a 
revised population estimate of 8,742 rather than the previously 
reported value of 5,812 (Doroff et al. in prep.). Finally, most 

[[Page 55695]]

estimates presented by the petitioners are not corrected for detection 
probability. Sea otters may either be at the surface and missed by 
observers, or below the surface and unavailable for counting. In order 
to calculate the best estimate of current population size for 
determination of depleted status, these data must be corrected for 
detection probability.
    Detection probability is often specific to survey design, 
personnel, and weather conditions. The survey technique used in Prince 
William Sound, Kodiak, and Yakutat generates a detectability correction 
factor for each survey (Bodkin and Udevitz 1999). Detection 
probabilities for this technique ranged from 52-72%. Similarly, the 
Aleutian Islands survey in 2000 used sea otter counts made from skiffs 
at six islands to estimate a detection probability of 28% (Doroff et 
al. in prep).
    For aerial and ship-based surveys for which no correction factor 
exists, the results of similar studies can be used as approximate 
values. For fixed-wing aerial surveys with one observer on each side of 
the aircraft, Evans et al. (1997) calculated that observers saw 42% of 
the sea otters within a known area. This equates to a detectability 
correction factor of 2.38 (CV=0.087). For surveys conducted from small 
boats, Udevitz et al. (1995) estimated that observers saw 70% of the 
sea otters present, for a correction factor of 1.43 (CV=0.071). 
Detection of sea otters during boat surveys is higher than aerial 
surveys because the survey platform is moving slower, which gives 
observers more time to visually search for otters. The additional 
search time also reduces the likelihood that otters below the surface 
may be missed. Using the most applicable correction factors for 
detection probability available, the best estimate for the Aleutians 
Islands, and including all areas of the State, the current best 
estimate of the Alaska sea otter population size is 74,143 with a 95% 
confidence interval of 15,739 (Table 1).

 Table 1.--Current Statewide Population Estimates of Sea Otters in Alaska. Original Estimates for Locations in Italics Did Not Include a Survey-Specific
  Detection Probability Correction Factor. Adjusted Estimates for These Locations Use a Correction Factor of 2.38 for Fixed-Wing Aircraft and 1.43 for
                                                                   Small Boat Surveys
               Location                  Survey          Survey type          Original        of        Adjusted                 Reference
                                          year                                estimate    variation     estimate
Southeast Alaska......................      1994  Small boat..............        8,180        0.392       11,697  Agler et al. 1995.
Yakutat Bay...........................      1995  Fixed-wing aircraft.....          404        0.339          404  Doroff and Gorbics 1998.
North Gulf of Alaska (Cape Yakataga to      1996  Fixed-wing aircraft.....          223  ...........          531  Doroff and Gorbics 1998.
 Cape Spencer).
Lower Cook Inlet......................      1993  Small boat..............        5,914        0.267        8,457  Agler et al. 1995.
Kenai Peninsula.......................      1989  Helicopter..............        2,330        0.120        2,330  DeGange et al. 1995.
Prince William Sound..................      1999  Fixed-wing aircraft.....       13,234        0.198       13,234  USGS unpublished data.
N. Gulf of Alaska (Cape Hinchinbrook        1996  Fixed-wing aircraft.....          271  ...........          645  Doroff and Gorbics 1998.
 to Cape Yakataga).
Aleutian Islands......................      2000  Fixed-wing aircraft.....        8,742        0.215        8,742  Doroff et al. in prep.
Unimak Island.........................      2001  Fixed-wing aircraft.....           42  ...........          100  FWS unpublished data.
North Alaska Peninsula (False Pass to       2000  Fixed-wing aircraft.....        5,756        0.327       13,699  FWS unpublished data.
 Port Heiden).
South Alaska Peninsula (False Pass to       2001  Fixed-wing aircraft.....          939        0.809        2,235  FWS unpublished data.
 Pavlof Bay).
South Alaska Peninsula (Seal Cape to        2001  Fixed-wing aircraft.....        2,190  ...........        5,212  FWS unpublished data.
 Cape Douglas).
South Alaska Peninsula Islands........      2001  Fixed-wing aircraft.....          405  ...........          964  FWS unpublished data.
Kodiak Archipelago....................      2001  Fixed-wing aircraft.....        5,893        0.228        5,893  FWS unpublished data.
                                       ----------                          ---------------------------------------
      Total...........................  ........  ........................  ...........  ...........       74,143  .....................................

Population Status Relative to OSP

    The worldwide population of sea otters in the early 1700s has been 
estimated at 150,000 (Kenyon 1969) to 300,000 (Johnson 1982). The size 
of the Alaska sea otter population prior to commercial depletion is 
unknown. Calkins and Schneider (1985) estimated the statewide sea otter 
population at 100,000 to 150,000 in 1976. Sea otter populations have 
potentially high reproductive rates (Riedman and Estes 1990). As a 
result, recovering otter populations may temporarily exceed carrying 
capacity (K) on a local level, before stabilizing at a lower 
equilibrium value (Estes 1990). These uncertainties make a current 
determination of K for sea otters in Alaska problematic. In the face of 
these uncertainties, the petitioners propose a conservative estimate of 
K for sea otters in Alaska of 100,000 individuals. Lacking specific 
information about habitat and K throughout much of Alaska, we believe 
this is a reasonable estimate of K at this time.
    Determination of the Maximum Net Productivity Level (MNPL), which 
defines the lower bound of Optimum Sustainable Population (OSP) for any 
marine mammal stock is difficult. Initial studies on marine mammal 
populations using a generalized logistic population model resulted in a 
MNPL of half of K. Later studies based on the life history 
characteristics of marine mammals suggested that MNPL lies somewhat 
closer to K (Eberhardt and Siniff 1977, Gerrodette and DeMaster 1990). 
For most species of marine mammals, there is insufficient data 
available to estimate MNPL accurately (Taylor and DeMaster 1993). Where 
a Species-specific estimate of MNPL is unavailable, the best available 
information calls for applying 60% of K as an approximation (Barlow et 
al. 1995). Using this approximation of MNPL (60%) for the purpose of 
responding to this petition and in the absence of specific productivity 
levels for Alaska sea otters and an estimated K of 100,000, the 
petitioners present a lower threshold of OSP for sea otters in

[[Page 55696]]

Alaska of 60,000. The best available population estimate for sea otters 
in Alaska (74,143) is above this threshold.

Finding on the Petitioned Action

    Based on the best available estimate of current population size, 
the statewide sea otter population is above the conservative estimate 
of OSP. In addition, although the last finalized stock assessment in 
1995 classified sea otters in Alaska as a single stock, the best 
scientific information currently available indicates that multiple 
stocks exist. This information suggests that three stocks occur in 
Alaska: Southwest, southcentral, and southeast. The best available 
scientific information shows that the population in southeast Alaska is 
growing (Bodkin et al. 1999), and the population in southcentral Alaska 
is either stable or growing. While these two populations are either 
stable or growing, the FWS acknowledge that sea otters in southwest 
Alaska have undergone widespread, dramatic declines in the past 10-15 
    The FWS is in the process of revising the stock assessment of sea 
otters in Alaska under the MMPA, and as part of this process will make 
a final determination on the number and geographic range of Alaska sea 
otter stocks. Stock identification is a defined process under the MMPA 
and while the currently available biological data indicates that three 
stocks are appropriate, the Service needs to complete the stock 
assessment process properly and in close cooperation with our partners. 
The genetics study conducted by the FWS was just recently completed and 
we expect the new stock assessments to be completed soon. Once these 
stock assessments are finalized, the status of each stock will be 
evaluated and designation of a southwest stock as depleted may be 
warranted at that time.
    The FWS acknowledged the decline of sea otters of the Aleutians by 
designating them a Candidate Species under the ESA in August 2000. In 
the candidate species designation, the FWS treated the sea otters in 
southwest Alaska as a distinct population segment under the ESA and its 
implementing regulations. Once funding is available the FWS will 
proceed to propose the southwest Alaska sea otters for Federal listing 
under the ESA. This action would be more applicable to the sea otter 
than a depleted designation. The primary benefits that accrue to a 
depleted species is the requirement for a conservationn plan which is 
already in place for the sea otter, and the ability to publish 
regulations to regulate harvest if harvest is negatively affecting the 
population; we do not believe harvest is affecting the population. 
Also, under section 3(1)(C) of the MMPA (16 U.S.C. 1362), a species or 
population stock that is listed as an endangered species or a 
threatened species under the ESA is automatically classified as 
depleted under the MMPA. While continuing to evaluate the sea otter 
under both statutes, the FWS will also continue to monitor population 
status and further assess causes of the decline, to the extent possible 
within available resources.
    The FWS finds that the petition did not present substantial 
information that the petitioned action is warranted. The FWS has 
determined that the statewide population of sea otters in Alaska is 
considerably larger than the conservative estimate of OSP presented in 
the petition. Furthermore, the best available scientific information 
indicates that multiple stocks of sea otter exist in Alaska.


    Agler, B.A., S.J. Kendall, P.E. Seiser, and D.B. Irons. 1995. 
Estimates of marine bird and sea otter abundance in lower Cook 
Inlet, Alaska, during summer 1993 and winter 1994. Migratory Bird 
Management, U.S. Fish and Wildlife Service, Anchorage, Alaska. 121 
    Agler, B.A., S.J. Kendall, P.E. Seiser, and J.R. Lindell. 1995. 
Estimates of marine bird and sea otter abundance in southeast Alaska 
during summer 1994. Migratory Bird Management, U.S. Fish and 
Wildlife Service, Anchorage, Alaska. 90 pp.
    Barlow, J., S.L. Swartz, T.C. Eagle, and P.R. Wade. 1995. U.S. 
marine mammal stock assessments: guidelines for preparation, 
background, and a summary of the 1995 assessments. U.S. Department 
of Commerce, NOAA Technical Memorandum NMFS-OPR-6. 73 pp.
    Bodkin, J.L. and M.S. Udevitz. 1999. An aerial survey method to 
estimate sea otter abundance. Pages 13-26. In: Marine Mammal Survey 
Assessment Methods. G.W. Garner et al. (Eds.) A.A. Balkema, 
    Bodkin, J.L., B.E. Ballachey, M.A. Cronin, and K.T. Scribner. 
1999. Population demographics and genetic diversity in remnant and 
translocated populations of sea otters (Enhydra lutris). 
Conservation Biology. 13(6)1378-1385.
    Brueggeman, J.J., G.A. Green, R.A. Grotefendt, and D.G. Chapman. 
1988. Aerial surveys of sea otters in the northwestern Gulf of 
Alaska and the southeastern Bering Sea. Minerals Management Service 
and NOAA Final Report. Anchorage, Alaska.
    Calkins, D.G. and K.B. Schneider. 1985. The sea otter (Enhydra 
lutris). Pages 37-45. In: Marine Mammals Species Accounts, J.J. 
Burns, K.J. Frost, and L.F. Lowry (Eds.). Alaska Department of Fish 
and Game, Technical Bulletin 7.
    Cronin, M.A., W.J. Spearman, W. Buchholz, S. Miller, L. Jack, 
and L.R. Comerci. In prep. Microsatellite DNA and mitochondrial DNA 
variation in Alaska sea otters.
    DeGange, A.R., D.C. Douglas, D.H. Monson, and C.M. Robbins. 
1995. Surveys of sea otters in the Gulf of Alaska in response to the 
Exxon Valdez oil spill. Natural Resource Damage Assessment Marine 
Mammal Study 6-7. Final Report. 11 pp.
    Dizon, A.E., C. Lockyer, W.F. Perrin, D.P. DeMaster, and J. 
Sisson. 1992. Rethinking the stock concept: a phylogeographic 
approach. Conservation Biology, 6: 24-36.
    Doroff, A.M. and C.S. Gorbics. 1998. Sea otter surveys of 
Yakutat Bay and adjacent Gulf of Alaska coastal areas--Cape 
Hinchinbrook to Cape Spencer 1995-1996. Minerals Management Service, 
OCS Study MMS 97-0026. pp.
    Doroff, A.M., J.A. Estes, M.T. Tinker, D.M. Burn, and T.J. 
Evans. In prep. Sea otter population declines in the Aleutian 
    Eberhardt, L.L. and D.B. Siniff. 1977. Population dynamics and 
marine mammal management policies. Journal of the Fisheries Research 
Board of Canada, 34: 183-190.
    Estes, J.A. 1990. Growth and equilibrium in sea otter 
populations. Journal of Animal Ecology 59: 385-401.
    Estes, J.A., M.T. Tinker, T.M. Williams, and D.F. Doak. 1998. 
Killer whale predation linking oceanic and nearshore ecosystems. 
Science 282: 473-476.
    Evans, T.J., D.M. Burn, and A.R. DeGange. 1997. Distribution and 
relative abundance of sea otters in the Aleutian Archipelago. U.S. 
Fish & Wildlife Service, Marine Mammals Management Technical Report, 
MMM 97-5. 29 pp.
    Gerrodette, T. and D.P. DeMaster. Quantitative determination of 
optimum sustainable population level. Marine Mammal Science, 6(1): 
    Gorbics, C.S. and J.L. Bodkin, 2001. Stock structure of sea 
otters (Enhydra lutris kenyoni) in Alaska. Marine Mammal Science, 
17(3): 632-647.
    Johnson, A.M. 1982. Status of Alaska sea otter populations and 
developing conflicts with fisheries. Trans. 47th North American 
Wildlife and Natural Resources Conference: 293-299.
    Kenyon, K.W. 1969. The sea otter in the eastern Pacific Ocean. 
U.S. Department of the Interior. North American Fauna, Number 68. 
352 pp.
    Riedman, M.L. and J.A. Estes. 1990. The sea otter (Enhydra 
lutris): behavior, ecology, and natural history. U.S. Fish and 
Wildlife Service, Biological Report 90(14). 126 pp.
    Rotterman, L.M. and T. Simon-Jackson. 1988. Sea otter (Enhydra 
lutris) Pages 237-275. In: Selected marine mammals of Alaska: 
species accounts with research and management recommendations. J.W. 
Lentfer (Ed.). Marine Mammal Commission, Washington, DC.
    Taylor, B.L. and D.P. DeMaster. 1993. Implications of non-linear 
density dependence. Marine Mammal Science, 9(4): 360-371.
    Udevitz, M.S., J.L. Bodkin, and D.P. Costa. 1995. Detection of 
sea otters in boat-based surveys of Prince William Sound, Alaska. 
Marine Mammal Science, 11(1): 9-71.
    Wilson, D.E. M.A. Bogan, R.L. Brownell, Jr., A.M. Burdin, and 
M.K. Maminov. 1991.

[[Page 55697]]

Geographic variation in sea otters, Enhydra lutris. Journal of 
Mammalogy 72: 22-36.

    Authority: The authority for this action is the Marine Mammal 
Protection Act of 1972, as amended, 16 U.S.C. 1361 et seq.

    Dated: October 26, 2001.
Marshall P. Jones, Jr.,
Director, U.S. Fish and Wildlife Service.
 [FR Doc. 01-27495 Filed 11-1-01; 8:45 am]