[Federal Register: December 30, 2008 (Volume 73, Number 250)]
[Page 79895-79898]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]



Fish and Wildlife Service

[FWS-R9-FHC-2008-N0287; 80221-1113-0000-L5]

Marine Mammal Protection Act; Stock Assessment Report

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Notice of availability of final 2008 revised marine mammal 
stock assessment report for the southern sea otter in California; 
response to comments.


SUMMARY: In accordance with the Marine Mammal Protection Act of 1972, 
as amended (MMPA), and its implementing regulations, we, the U.S. Fish 
and Wildlife Service (Service), announce that we have revised our stock 
assessment report (SAR) for the southern sea otter (Enhydra lutris 
nereis) stock in California State, including incorporation of public 
comments. We now make our complete final 2008 revised SAR available to 
the public.

FOR FURTHER INFORMATION CONTACT: For information on the methods, data, 
and results of the stock assessment, contact Lilian Carswell by phone 
at (805) 612-2793 or by e-mail at Lilian_Carswell@fws.gov.

ADDRESSES: Send requests for printed copies of the SAR to: Field 
Supervisor, U.S. Fish and Wildlife Service, Ventura Fish and Wildlife 
Office, 2493 Portola Road, Suite B, Ventura, CA 93003. You may also 
view or download it at http://www.fws.gov/ventura/speciesinfo/so_sea_

SUPPLEMENTARY INFORMATION: Under the MMPA (16 U.S.C. 1361 et seq.) and 
its implementing regulations in the Code of Federal Regulations at 50 
CFR part 18, we regulate the taking, possession, transportation, 
purchasing, selling, offering for sale, exporting, and importing of 
marine mammals. One of the goals of the MMPA is to ensure that stocks 
of marine mammals occurring in waters under the jurisdiction of the 
United States do not experience a level of human-caused mortality and 
serious injury that is likely to cause the stock to be reduced below 
its optimum sustainable population level (OSP). OSP is defined as ``the 
number of animals which will result in the maximum productivity of the 
population or the species, keeping in mind the carrying capacity of the 
habitat and the health of the ecosystem of which they form a 
constituent element.''
    To help accomplish the goal of maintaining marine mammal stocks at 
their OSPs, section 117 of the MMPA

[[Page 79896]]

requires us and the National Marine Fisheries Service (NMFS) to prepare 
a SAR for each marine mammal stock that occurs in waters under the 
jurisdiction of the United States. A SAR must be based on the best 
scientific information available; therefore, we prepare it in 
consultation with established regional scientific review groups. Each 
SAR must include: (1) A description of the stock and its geographic 
range; (2) minimum population estimate, maximum net productivity rate, 
and current population trend; (3) estimate of human-caused mortality 
and serious injury; (4) commercial fishery interactions; (5) status of 
the stock; and (6) potential biological removal (PBR) level. The PBR is 
defined as ``the maximum number of animals, not including natural 
mortalities, that may be removed from a marine mammal stock while 
allowing that stock to reach or maintain its OSP.'' The PBR is the 
product of the minimum population estimate of the stock 
(Nmin); one-half the maximum theoretical or estimated net 
productivity rate of the stock at a small population size 
(Rmax); and a recovery factor (Fr) of between 0.1 
and 1.0, which is intended to compensate for uncertainty and unknown 
estimation errors.
    Section 117 of the MMPA also requires us and NMFS to review the 
SARs (a) At least annually for stocks that 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.
    A strategic stock is defined in the MMPA as a marine mammal stock 
(A) For which the level of direct human-caused mortality exceeds the 
PBR; (B) which, based on the best available scientific information, is 
declining and is likely to be listed as a threatened species under the 
Endangered Species Act of 1973, as amended (16 U.S.C. 1531 et seq.; 
ESA), within the foreseeable future; or (C) which is listed as a 
threatened or endangered species under the ESA, or is designated as 
depleted under the MMPA.
    Before releasing our draft SAR for public review and comment, we 
submitted it for technical review internally and also for scientific 
review by the Pacific Regional Scientific Review Group, which was 
established under the MMPA. In a June 10, 2008 (73 FR 32732), Federal 
Register notice, we made available our draft SAR for the MMPA-required 
90-day public review and comment period. Following the close of the 
comment period, we revised the SAR based on public comments we received 
(see below) and prepared the final 2008 revised SAR. Between 
publication of the draft and final revised SARs, we have not revised 
the status of the stock itself (i.e., strategic). However, in response 
to a public comment, we revised Nmin to base it on the 20th 
percentile of the log-normal distribution of the average count for the 
3-year running average for 2006-2008. In addition, rather than listing 
the Nmin, of the mainland and the San Nicolas Island 
populations separately, we combined them into a single Nmin, 
for the stock as a whole. We used an Rmax of 6 percent, that 
of the mainland population, because this rate reflects the threats and 
limitations to which approximately 98 percent of the stock is exposed. 
We revised the PBR level from 9 to 8 based on an Rmax of 6 
percent and the revised Nmin. We addressed most of the 
public comments we received by adding text for clarity.
    The following table summarizes the final 2008 revised SAR for 
southern sea otters in California, listing the stock's Nmin, 
Rmax, Fr, PBR, annual estimated human-caused 
mortality and serious injury, and status:

                                Summary of Final Revised Stock Assessment Report for the Southern Sea Otter in California
                                                                                                 Annual estimated average
                 Stock                      Nmin          Rmax           Fr            PBR        human-caused mortality            Stock status
Southern sea otters...................        2,723          0.06           0.1             8   Unknown..................  Strategic.

Responding to Public Comments

    We received comments on the draft SAR (73 FR 32732) from the Marine 
Mammal Commission, the Center for Biological Diversity, Friends of the 
Sea Otter, Defenders of Wildlife, and one private citizen. We present 
issues raised in those comments, along with our responses, below.
    Comment 1: Because of the uncertainty in population counts, the 
decline in the 2008 sea otter count, and the absence of routine updates 
to the SAR, the Service should take a precautionary approach and base 
the minimum population size estimate on the 20th percentile of the log-
normal distribution of the average count for the 3-year running average 
for 2006-2008 rather than the latest single-year count.
    Response: Our use of the latest single-year count in the draft SAR 
was based on the Guidelines for Preparing Stock Assessment Reports 
Pursuant to Section 117 of the Marine Mammal Protection Act (GAMMS II), 
published in 2005, which state that a direct count may be used as an 
estimate for Nmin. We acknowledge that there are 
considerable fluctuations in the population count from year to year, 
resulting in part from unquantifiable observation error. Because of 
this year-to-year variability, the 3-year running average is the metric 
recommended in the final revised recovery plan for the southern sea 
otter (68 FR 16305; April 3, 2003), and it is the metric we typically 
use to characterize population size and to track trends. However, use 
of the 3-year running average as a minimum population size estimate for 
the purposes of the SAR is not appropriate, because the MMPA defines 
Nmin as the number that provides reasonable assurance that 
the stock size is equal to or greater than the estimate. If a high 
count is followed by 2 years of declining counts, it is possible that 
the 3-year running average will not provide reasonable assurance that 
the stock size is equal to or greater than the estimate. Therefore, we 
adopt the precautionary approach recommended by the commenter, which 
applies the alternate guidelines for determining Nmin that 
are included in the GAMMS II guidance. To calculate Nmin for 
the stock, we combined counts for the mainland and San Nicolas Island. 
Given the log-normal distribution of the average combined counts for 
2006-2008, the estimate corresponding to the 20th percentile of this 
distribution is 2,723. We have revised the minimum population estimate 
    Comment 2: The Service should include an estimate of the average 
population size as well as a minimum population estimate.
    Response: The data resulting from the annual spring surveys 
represent minimum population counts, with no associated correction 
factor or variance estimate. As a result, they include significant (but 
unquantifiable) observation error, probably caused mostly by year-to-
year variance in survey conditions. In order to reduce potential 
influences from the vagaries of any single census, data are presented 

[[Page 79897]]

3-year running averages. In response to comments we received on our 
draft SAR (73 FR 32732), we now base the minimum population estimate on 
the 20th percentile of the log-normal distribution of the average count 
for 2006-2008 rather than on the most recent census. However, because 
correction factors or variance estimates are not available, we are 
unable to include an estimate of the average population size.
    Comment 3: The SAR should clarify that the San Nicolas Island 
colony is considered to be a ``non-essential experimental population'' 
under the ESA because it was established during a translocation 
experiment (52 FR 29754; August 11, 1987). It should also clarify 
whether this population was included in the estimation of population 
parameters used to characterize the stock's status and to determine its 
PBR level.
    Response: We have revised the SAR accordingly.
    Comment 4: The Service should arrange for observer coverage of trap 
fisheries for lobster, crab, and fish, particularly in waters occupied 
by sea otters south of Point Conception, and of set and drift gillnet 
fisheries in the sea otter's range. Observer coverage should be 
augmented in the purse-seine fisheries.
    Response: NMFS conducts observer programs. Since resources for 
these programs are fully utilized, no new programs may be initiated 
until other monitoring or conservation efforts are terminated so that 
resources can be redirected. A recent analysis has shown that a very 
high level of observer coverage would be required to see any indication 
of trap mortality, even if mortality levels were high enough to 
substantially reduce the rate of population recovery (Hatfield et al., 
in prep.). We are evaluating options for obtaining additional 
information on interactions between sea otters and fisheries that have 
limited or no observer coverage.
    Comment 5: The Service assumes that mortalities from gill nets are 
``at or near zero'' based on the closure of some areas to gill net use 
but lacks the observer and other independent data to back up this 
assumption. The Service cannot legitimately claim that entanglements 
are at or near zero based on the limited observer data available.
    Response: We believe that southern sea otter mortalities resulting 
from interactions with gill nets are currently at or near zero because 
of the relationship between three factors: The depths that are closed 
to gill net fishing; the depths utilized by sea otters for foraging; 
and the current extent of the southern sea otter's range. Gill net 
fishing is prohibited in waters shallower than 70 fathoms (128 meters) 
from Point Reyes to Point Arguello, in waters generally within 3 
nautical miles offshore of the mainland coast from Point Arguello to 
the Mexican border, and in waters shallower than 70 fathoms or within 1 
mile, whichever is less, around the Channel Islands. Although sea 
otters occasionally dive to depths of 100 meters, the vast majority 
(more than 99 percent) of dives are to depths of 40 meters or less (M. 
Tim Tinker, pers. comm., 2008). The southern sea otter range currently 
extends from the mouth of the Tunitas Creek, in San Mateo County, to 
Coal Oil Point, in Santa Barbara County (http://www.werc.usgs.gov/
otters/ca-surveyspr2008.htm). The closure from Point Reyes to Point 
Arguello, which includes most of the sea otter range, encompasses the 
depths to which southern sea otters are known to dive. The remainder of 
the range is located along the coast from Point Arguello to Coal Oil 
Point. The bathymetry of the area from Point Arguello to Coal Oil Point 
is such that the 3-mile closure translates into depths of approximately 
100 meters. A preliminary analysis of sea otter dives in the southern 
portion of the range determined that a closure to 94 meters would 
include all dives of 95 percent of all sea otters, and a closure to 104 
meters would include all dives of 99 percent of all sea otters (M. Tim 
Tinker, pers. comm., 2008). Because the likelihood of a sea otter 
diving to depths exceeding 128 or 100 meters is exceedingly small, we 
do not believe that, given the current extent of the range, sea otters 
are interacting with gill nets. However, we will continue to evaluate 
the risks to which sea otters are exposed by this type of gear.
    Comment 6: The Service reports three non-lethal interactions in 
purse-seine fisheries over the past 5 years but assumes that no serious 
injuries or mortalities have occurred. This assumption seems overly 
    Response: We have revised the SAR to reflect that no data are 
available to enable us to assess whether sea otter interactions with 
purse-seine gear are resulting in mortality or serious injury.
    Comment 7: Because sea otters are not covered under section 118 of 
the MMPA, PBR does not apply to the governance of incidental take of 
southern sea otters in commercial fisheries. However, section 117 of 
the MMPA requires the calculation of PBR, and that calculation should 
be based on the best available scientific data. Therefore, the Service 
should use a value for Rmax of 5 percent rather than 6 
percent to calculate PBR, because the average annual growth rate from 
2001 to 2007 was approximately 5 percent.
    Response: We have revised the SAR to clarify the status of southern 
sea otters with respect to section 118 of the MMPA. However, we have 
not used an Rmax of 5 percent as suggested by the commenter. 
The MMPA defines one-half Rmax as ``one-half of the maximum 
theoretical or estimated `net productivity rate' of the stock at a 
small population size,'' where the term ``net productivity rate'' means 
``the annual per-capita rate of increase in a stock resulting from 
additions due to reproduction, less losses due to natural mortality.'' 
The maximum observed growth rate along the mainland is 6 percent 
annually. Although the maximum observed growth rate in any southern sea 
otter population is 9 percent annually, this rate has been seen only at 
San Nicolas Island, which is geographically removed from the mainland 
range and is subject to different threats and limitations than the 
mainland range. For the stock as a whole, we use an Rmax of 
6 percent rather than 9 percent because that rate reflects the threats 
and limitations to which approximately 98 percent of the population is 
    Comment 8: It is misleading to say that the colony at San Nicolas 
Island ``has grown by approximately 9 percent annually'' since the 
early 1990s. It would be accurate to say that the colony has grown by 
``an approximate average of 9 percent annually'' since the early 1990s.
    Response: We have revised the SAR accordingly.
    Comment 9: The Service does not provide an estimated number of non-
lethal interactions or a precise estimate of observer coverage in the 
purse-seine fishery for 2006.
    Response: The SAR has been revised to incorporate an estimated 
number of non-lethal interactions in 2006. A precise estimate of 
observer coverage in the purse-seine fishery for 2006 requires data on 
fishing effort derived from logbook and landing data. At the time the 
final SAR was prepared, logbook and landing data for purse seine 
fisheries targeting sardine, anchovy, mackerel, and tuna in 2006 were 
not available.
    Comment 10: The SAR should reference the unpublished study that 
analyzed sea otter carcasses and their ability to fit through a variety 
of trap openings.
    Response: We have included results from the referenced study 
(Hatfield et al., in prep.) in the final SAR.

[[Page 79898]]

    Comment 11: The Service should take every action available to 
investigate and, where possible, mitigate the impact of infectious 
disease and should improve enforcement of the provisions of the MMPA 
that prevent the intentional shooting of marine mammals.
    Response: We support and have provided funding for studies aimed at 
determining and mitigating the impact of infectious disease. We 
continue to investigate, and pursue actions in response to, intentional 
shooting of sea otters.
    Comment 12: While section 118 of the MMPA does not govern the 
incidental taking of southern sea otters, the zero mortality rate goal 
(ZMRG) provisions in section 101 do apply to southern sea otters. The 
fact that the Service cannot make a status determination with respect 
to ZMRG confirms that ZMRG has not been achieved for sea otters and 
that the Service has not satisfied its requirements under the law. This 
failure strongly supports the need for [the Service] to aggressively 
place observers on fisheries that have the potential to take southern 
sea otters so that it can determine the status of the stock with 
respect to ZMRG.
    Response: Please see our response to comment 4.
    Comment 13: The SAR should provide additional discussion and 
references on the topic of food limitation and nutritional deficiency.
    Response: We have included additional references in the final SAR 
and will expand our discussion as data become available.
    Additional References Cited:

Bentall, G.B., 2005. Morphological and Behavioral Correlates of 
Population Status in the Southern Sea Otter: A Comparative Study 
Between Central California and San Nicolas Island. Masters Thesis, 
University of California, Santa Cruz, CA, unpublished.
Hatfield, B.B., J.A. Ames, J.A. Estes, M.T. Tinker, A.B. Johnson, M.M. 
Staedler, and M.D. Harris. Manuscript in preparation. The potential for 
sea otter mortality in fish and shellfish traps. 22 pp. + appendices.

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

    Dated: December 17, 2008.
Kenneth Stansell,
Acting Director, Fish and Wildlife Service.
[FR Doc. E8-31022 Filed 12-29-08; 8:45 am]