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Marine Mammal Protection Act; Stock Assessment Reports

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Fish and Wildlife Service, Interior.


Notice of availability of final revised marine mammal stock assessment reports for three stocks of northern sea otters in Alaska; response to comments.


In accordance with the Marine Mammal Protection Act (MMPA), the Fish and Wildlife Service (Service) has incorporated public comments into revisions of marine mammal stock assessment reports for the three stocks of northern sea otters (Enhydra lutris kenyoni) in Alaska. The 2008 final stock assessment reports are now complete and available to the public.


Send requests for printed copies of the final stock assessment reports to: Chief, U.S. Fish and Wildlife Service, Marine Mammals Management Office, 1011 East Tudor Road, Anchorage, AK 99503; (800) 362-5148. Copies of the final revised stock assessment reports are also available on the Internet in Adobe Acrobat format at​fisheries/​mmm/​seaotters/​reports.htm.

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One of the goals of the MMPA (16 U.S.C. 1361-1407) 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 requires the Service and the National Marine Fisheries Service (NMFS) to prepare stock assessment reports for each marine mammal stock that occurs in waters under the jurisdiction of the United States. These stock assessments are to be based on the best scientific information available and are, therefore, prepared in consultation with established regional scientific review groups. Each stock assessment 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 level (PBR). 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 the Service and the NMFS to review and revise the stock assessment reports: (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 Start Printed Page 45239scientific information, is declining and is likely to be listed as a threatened species under the Endangered Species Act of 1973 (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.

Draft 2008 stock assessment reports for the 3 Alaska stocks of northern sea otters were made available for a 90-day public review and comment period on February 6, 2008 (73 FR 6994). Prior to releasing them for pubic review and comment, the Service subjected the draft reports to internal technical review and to scientific review by the Alaska Regional Scientific Review Group established under the MMPA. Following the close of the comment period, the Service revised the stock assessments and prepared the final 2008 stock assessment reports.

We revised these final stock assessment reports based on public comments received (see below). The status of each stock remained unchanged from the draft revised SARs that were provided for public comment, and with the exception of the southwest Alaska stock, PBR levels were not changed. Estimates of fishery-related mortality and serious injury have been revised for all three stock assessment reports. We addressed responses to most of the public comments by adding new text for clarity.

A summary of the final revised stock assessment reports is presented in Table 1. The table lists each stock's Nmin, Rmax, Fr, PBR, annual estimated human-caused mortality and serious injury, and status.

Table 1—Summary of Final Revised Stock Assessment Reports for Three U.S. Northern Sea Otter Stocks

StockNMINRMAXFRPBRSerious injuryAnnual 5-year estimated human-caused mortalityStock status
Northern sea otters (Southeast AK)9,1360.201.09140Unknown322Non-strategic
Northern sea otters (Southcentral AK)12,7740.201.01,2770Unknown346Non-strategic
Northern sea otters (Southwest AK)38,7030.200.13870<1091Strategic

Comments and Responses

The Service received 3 comments on the drafts stock assessment reports. The issues raised in those comments and our responses are provided below.

Comment 1: The use of a recovery factor of 0.25 for the southwest Alaska stock is too high; a recovery factor of 0.1 should be used instead.

Response: The choice of recovery factors for population stocks that are declining is complex. The southwest Alaska stock is currently listed as threatened under the ESA and the current population trend is one of decline. Therefore, we agree with this comment to take a more conservative approach and have reduced the recovery factor for the southwest Alaska stock to 0.1, which lowers the PBR to 387.

Comment 2: Given that one otter was self-reported by the fisher to have been caught in a trawl fishery, the conclusion that “estimated level of incidental motality and serious injury associated with Alaska trawl, longline, and pot groundfish fisheries is zero” is not accurate.

Response: Available information on this self-reported incident is unclear whether the otter was caught and killed in the trawl fishery, or was a dead animal that was simply caught by the trawl. The text of the southwest Alaska stock assessment has been revised to say that the “estimated level of incidental morality and serious injury associated with Alaska trawl, longline, and pot groundfish fisheries averages less than one animal per year.”

Comment 3: The estimate that mortality and serious injury in the Kodiak salmon set net fishery is less than one animal per year is not accurate.

Response: This section of the southwest Alaska stock assessment report has been revised to indicate that the level of mortality and serious injury rate for this fishery is likely no more than 10 animals per year.

Comment 4: Information is insufficient to conclude that fishery impacts on the southcentral and southeast Alaska stocks is insignificant and approaching a zero mortality rate.

Response: We have revised the southcentral and southeast Alaska stock assessment reports to more accurately characterize the uncertainties in the level of fishery mortality and serious injury.

Comment 5: The Service should update stock assessment reports on the schedule specified under section 117 of the MMPA.

Response: The Service will continue to review available information on an annual basis and revise stock assessment reports for the northern sea otter in Alaska as appropriate.

Comment 6: The Service should review available information on sea otter stock structure in Alaska.

Response: Information on stock structure is driven primarily by genetic analysis of tissue samples. The most recent study of this nature was conducted in 2002. Since that time, more sample material has been collected during live-capture studies in the Kodiak archipelago (southwest Alaska stock) and Kamishak Bay (southcentral Alaska stock). Additional tissue samples from other areas are required, especially Kamishak Bay and the Alaska Peninsula adjacent to Shelikof Strait, before sea otter stock structure in Alaska can be analyzed.

Comment 7: Methods used to estimate sea otter abundance are not adequately described.

Response: The methods used to estimate sea otter abundance are thoroughly described in the references used to prepare these stock assessment reports. We believe it is redundant to describe them more comprehensively in the stock assessment reports.

Comment 8: Description of fishery interactions is incomplete; the stock assessment reports should list all fisheries known to interact with sea otters.

Response: We have included the relevant fisheries from the NOAA—Fisheries “List of Fisheries” that had previously been incorporated by reference.

Comment 9: Stock assessment reports do not adequately consider possible interactions in fisheries that are not Start Printed Page 45240observed or where observer coverage is low.

Response: The predominant type of fishing gear that has been known to interact with sea otters are salmon set and drift gillnets. Available information suggests that fisheries using other types of gear, such as trawl, longline, pot, and purse seine appear to be less likely to have interactions with sea otters due to either the areas where such fisheries operate, or the specific gear used, or both. Gillnet fisheries occur throughout the range of sea otters in Alaska; however, the nature of their potential for interaction depends on several factors including sea otter distribution and abundance relative to the distribution and effort expended in these fisheries. We believe that application of entanglement rates derived from small sample sizes in observed fisheries to unobserved fisheries in other areas would produce questionable results.

Comment 10: Stock assessment reports do not consider other impacts from oil and gas development besides oil spills.

Response: We considered disturbance from oil and gas exploration, development, and production in the draft stock assessments; however, we did not state this point explicitly in the draft stock assessment reports. We have revised the final stock assessment reports accordingly.

Comment 11: Fuel oil spills from ship traffic should be considered for the southcentral and southeast Alaska stocks.

Response: We have included additional information from the Alaska Department of Environmental Conservation spill reporting database about ship traffic and other sources that have resulted in discharges of crude and noncrude oil into the marine environment for all 3 stock assessment reports.

Comment 12: The stock assessment reports should describe the reasons for and implications of the age/sex distribution of the subsistence harvest on the demography and dynamics of sea otter populations.

Response: We believe the suggested additional in-depth analysis of the subsistence harvest is beyond the scope of these reports as it relates to determining the status of the stocks.

Comment 13: The impact of other factors, such as contaminants, should be evaluated.

Response: Available information is insufficient to quantitatively estimate the impacts of these factors.

Comment 14: Additional detail on the Unusual Mortality Event should be included in the stock assessment reports.

Response: Studies of sea otter disease, mortality, and survival are ongoing. Results are not yet available for inclusion in this stock assessment report.

Comment 15: Given the dates of the various surveys used to estimate the population size of the southwest Alaska stock, the current population may be lower than the estimated value.

Response: We acknowledge that population estimates for some of the regions within the southwest Alaska stock are somewhat dated; however, they are the best available scientific information at this time. Population monitoring for this stock is an important component of the recovery plan that is in development. As this stock is listed as threatened under the ESA, it is considered strategic under the MMPA and subject to annual review, regardless of the actual population size.

Comment 16: Apparent regional population trends in the southeast Alaska stock should be discussed in greater detail.

Response: The U.S. Geological Survey collected survey information for the southeast Alaska stock. A summary report that addresses this issue is in preparation; however, conclusions are not available at this time.

Comment 17: Information gathered from the fishing industry cannot be relied upon for truthfulness or accuracy because of their concern for profits.

Response: The Service relied on the best available scientific information in the preparation of these stock assessment reports, and readily acknowledges the limitations of these data. Although some of the information is self-reported, we also rely on fisheries observer programs when available.

Comment 18: The agency's system for observing the catch is incorrect and untruthful. Cameras on boats and fines and jail times are needed.

Response: Observer programs are conducted by the National Marine Fisheries Service of the Department of Commerce. We have forwarded these suggested improvements to them for consideration.

Comment 19: The words “optimum sustainable population” are opposed as the phrase promotes overutilization of the wildlife.

Response: The term “Optimal Sustainable Population” is defined in the Marine Mammal Protection Act (16 U.S.C. 1362).

References Not Cited in the Notice of Availability of Draft Revised SARs

Manly, B.F.J. 2006. Incidental catch and interactions of marine mammals and birds in the Cook Inlet salmon driftnet and setnet fisheries. Western EcoSystems Technology Inc. Report. Cheyenne, Wyoming, USA. 98pp.

Manly, B.F.J. 2007. Incidental take and interactions of marine mammals and birds in the Kodiak Island salmon set gillnet fishery, 2002 and 2005. Western EcoSystems Technology Inc. Report. Cheyenne, Wyoming, USA. 221pp.

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Authority: The authority for this action is the Marine Mammal Protection Act of 1972, as amended (16 U.S.C. 1361-1407).

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Dated: July 29, 2008.

Rowan W. Gould,

Acting Director, Fish and Wildlife Service.

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[FR Doc. E8-17804 Filed 8-1-08; 8:45 am]