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Notice of Availability of Final Stock Assessment Reports

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Fish and Wildlife Service, Interior.


Notice of availability of final marine mammal stock assessment reports for Pacific walrus, polar bear, and sea otter in Alaska; response to comments.


In accordance with the Marine Mammal Protection Act (MMPA), the Fish and Wildlife Service (FWS) has incorporated public comments into revisions of marine mammal stock assessment reports (SARs) for Pacific walrus, polar bear, and sea otter in Alaska. The 2002 final SARs 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.

Electronic Access

Copies of the final stock assessment reports are available on the Internet in Adobe Acrobat format at​mmm/​SAR.

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Section 117 of the MMPA (16 U.S.C. 1361-1407) requires the FWS 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. Section 117 of the MMPA also requires the FWS and the NMFS to review 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 three years for all other stocks. If the review indicates that the status of the stock has changed or can be more accurately determined, the agencies are directed to revise the SARs. We published the initial SARs in 1995 and revised SARs for Pacific walrus and polar bears in 1998.

Draft 2002 SARs were made available for a 90-day public review and comment period on March 28, 2002 (67 FR 14959). Prior to releasing them for public review and comment, FWS subjected the draft reports to internal technical review and to scientific review Start Printed Page 62980by the Alaska Regional Scientific Review Group (ASRG) established under the MMPA. Following the close of the comment period, FWS revised the stock assessments and prepared the final 2002 SARs.

Previous stock assessments covered a single stock of Pacific walrus, two stocks of polar bears (Chukchi/Bering seas and Southern Beaufort Sea), and a single stock of sea otters in Alaska. There are no changes in stock identification for Pacific walrus and polar bear, however three stocks of sea otters (southwest Alaska, southcentral Alaska, and southeast Alaska) have now been identified.

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 potential biological removal level; (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 within the foreseeable future; or (C) which is listed as a threatened or endangered species under the Endangered Species Act of 1973, or is designated as depleted under the MMPA.

Only the southwest Alaska stock of sea otters was classified as strategic. All other stocks were classified as non-strategic. Based on the best available scientific information, sea otter numbers across southwest Alaska are declining. In April 2000, an aerial survey of sea otters in the Aleutian Islands indicated the population had declined by 70% during the period from 1992-2000. In August 2000 FWS designated the northern sea otter in the Aleutian Islands as a candidate species under the Endangered Species Act. Additional surveys in 2000 and 2001 along the Alaska Peninsula and Kodiak archipelago also showed population declines in these areas. As a result, the southwest Alaska stock is classified as strategic in the final report and is under review for possible listing under the Endangered Species Act.

A summary of the final revised stock assessment reports is presented in Table 1. The table lists each marine mammal stock, estimated abundance (NEST), minimum abundance estimate (NMIN), maximum theoretical growth rate (RMAX), recovery factor (FR), Potential Biological Removal (PBR), annual estimated average human-caused mortality, and the status of each stock.

Table 1.—Summary of Final Stock Assessment Reports for Pacific Walrus, Polar Bear, and Sea Otter in Alaska

SpeciesStockNESTNMINRMAXERPBRMortality causes (5 yr. average)Stock status
Pacific WalrusAlaska0.085,78914Non-strategic.
Polar BearAlaska Chukchi/Bering Seas0.060.545 (Alaska) 100+ (Russia)00 (Alaska) — (Russia)Non-strategic.
Polar BearAlaska Southern Beaufort Sea2,2721,9710.061.08834 (Alaska) 20 (Canada)0<1 (Alaska) 0 (Canada)Non-strategic.
Sea OtterSoutheast Alaska12,6329,2660.201.092730100Non-strategic.
Sea OtterSouthcentral Alaska16,55213,9550.201.01,39629700Non-strategic.
Sea OtterSouthwest Alaska41,47433,2030.200.2583097<10Strategic.
Dash(—)indicates unknown value.

Comments and Responses

FWS received 4 letters containing comments for sea otters, 3 letters for Pacific walrus, and two letters for polar bears. The comments and responses are separated below by species.

Sea Otter Stock Assessment Reports

Comment 1: One commenter noted that the calculation of Nmin for some sea otter surveys does not incorporate available estimates of sampling variance.

Response: We revised our approach to estimating Nmin for surveys that are uncorrected for sea otters not detected by observers by applying generic correction factors appropriate for the type of survey. This approach is consistent with our finding on a recent petition to list sea otters in Alaska as depleted under the MMPA (66 FR 55693, November 2, 2001)

Comment 2: Several commenters noted that the population estimates for the Cook Inlet and Kenai Fiords areas are outdated, do not conform to the established stock boundaries, and include duplication of effort in Kachemak Bay.

Response: We have substituted recent population estimates for these areas that remedy these problems.

Comment 3: One commenter indicated that the population estimate for much of the southeast Alaska stock is outdated.

Response: The survey in question is 7 years old. Stock Assessment guidelines state that abundance estimates older than 8 years are not reliable. Although it is still acceptable for use in the current stock assessment, we recognize the limitations of the existing data and have requested the U.S. Geological Survey, Division of Biological Resources, to conduct an aerial survey of sea otters in southeast Alaska. This survey is currently underway, and will be completed in sections over the next 2-3 years.

Comment 4: One commenter recommended that sea otter population estimates would be clearer if they were presented in tabular form.

Response: Tables of survey results have been included in the final stock assessment reports for sea otters.

Comment 5: Several commenters noted that sea otter population estimates included unpublished data.

Response: Typically peer-reviewed journals follow a 1-2 year cycle from manuscript preparation to submission to acceptance to publication. We believe that presentation of recent unpublished survey results, from surveys we conducted, is preferable than using older published estimates, and more appropriately meets the standard of “the best scientific information available.”

Comment 6: One commenter stated that the observed sea otter population growth rate of 12% for the Cross Sound/Start Printed Page 62981Icy Strait region may not be representatives of the entire southeast Alaska stock.

Response: We agree and have added text to clarify this point.

Comment 7: One commenter was concerned the fisheries information does not include information about fisheries that have the potential to interact with sea otters.

Response: Section 117(a)(4) of the Act states that stock assessment shall “deserve commercial fisheries that interact with the stock.” We interpret this to mean those fisheries for which we have information about interactions, not fisheries with the potential for interaction as suggested above. We see little value in speculating as to which fisheries might interact with sea otters. For a detailed list of fisheries and marine mammal interactions, the reader is directed to NMFS Continuing List of Fisheries [67 FR 2410, January 17, 2002]. The FWS relies on NMFS to provide us with estimates of fishery interactions. For further details on the limitations of these data, the reader is directed to the most recent NMFS Notice of Availability of Final Stock Assessment Reports [67 FR 10671, March 8, 2002].

Comment 8: Several commenters noted harvest estimates from the marine mammal Marking, Tagging, and Reporting Program may be biased low to an unknown degree due to incomplete hunter compliance.

Response: We believe this potential source of bias is extremely small for the following reason. Sea otters are hunted for their pelts, which must be tanned before they can be fashioned into handicrafts, and commercial tanneries will not accept untagged pelts. For accuracy, we have inserted the word “Estimated” into figure legends for subsistence harvest.

Comment 9: One commenter noted that information about the number of sea otters captured and released for scientific research was not quantified.

Response: Statistics on capture and release for scientific research have been included.

Pacific Walrus Stock Assessment Report

Comment 10: One commenter noted that the section “Current and maximum net productivity rates” referred to a study by University of Alaska researchers to investigate the reproductive rates of free-ranging walrus herds. The commenter recommended that the reproductive rates and/or juvenile survival rates observed in these studies be reported in the SAR.

Response: The FWS has concluded that these data are too preliminary for inclusion in the 2001 SAR and has removed all references to this study. The FWS will reconsider including this information in future SAR's once the study is complete.

Comment 11: Two commenters recommended making changes to the section “Conservation issues and habitat concerns” in reference to the issue of global warming and its potential impacts to the Pacific walrus population.

Response: At the present time there are no data available to make reliable predictions of the net impacts that changing climate conditions might have on the status and trend of the Pacific walrus population. The text of the SAR has been modified to clarify this point.

Comment 12: One commenter noted that the SAR underestimated struck-and-lost rates for subsistence-harvested animals and questioned the accuracy of the sex-ratio reported for the walrus harvest in Alaska. The commenter refers to recent FWS harvest monitoring field reports, describing harvest monitoring activities in the Bering Strait region, that suggest that self-reporting of struck-and-lost rates are likely to be negatively biased and describe a harvest with a skewed sex-ratio favoring females and dependent calves.

Response: Due to potentially negative bias associated with self-reporting of struck-and-lost rates, the FWS did not include this data in the SAR. The struck-and-lost estimate reported in the SAR is based on a published study describing the number of walrus struck and lost during monitored subsistence hunts in Alaska (Fay et al. 1994), The annual field reports referred to by the commenter describe a subset of the annual subsistence walrus harvest in Alaska. Although the spring hunt in these Bering Strait communities is frequently characterized by a sex-ratio skewed towards females, the sex ratio of the state-wide harvest over the 5-year period described in the 2001 SAR (1996-2000) was near parity. The source of the sex-ratio information was the FWS Marking, Tagging, and Reporting Program, which is a State-wide, year-round program that requires subsistence hunters to report the age and gender of all harvested walrus to the FWS. The source of the sex-ratio information was referenced in the text for clarity.

Comment 13: One commenter noted that the 42% struck-and-lost rate described in the SAR was based on data at least eight years old and speculated that this rate may change over time due to changes in hunting conditions and practices. The commenter recommended that this assumption should be verified from time to time and modified accordingly if it is found to change.

Response: In the absence of more recent scientific data, the FWS has chosen to use the published 42% rate for struck-and-lost animals as the best available scientific information for calculation of total harvest levels. However, the FWS agrees with the commenter that it is important to update or verify this struck-and-lost information periodically. The FWS hopes to initiate cooperative studies with the Eskimo Walrus Commission to examine struck-and-lost rates in the near future.

Comment 14: One commenter recommended that the draft stock assessment should emphasize that the Pacific walrus population may be in decline, even as the subsistence hunt continues to take a very large number of animals.

Response: The current size and trend of the Pacific walrus population is unknown. In the absence of new survey information, it is not possible to make reliable predictions regarding population trend.

Comment 15: One commenter noted that Russian officials consider the level of fisheries interaction to the small. The commenter felt this statement could be reassuring or misleading and recommended that the statement that the level of take in Russian waters is undetermined.

Response: We agree and have changed the text in the SAR to indicate that there are no data available concerning the incidental catch of walrus in fisheries operating in Russian waters.

Comment 16: One commenter noted that the section on “Fisheries information” refers to trawl and longline fishery interactions, but does not distinguish the level of takes between two gear types or the multiple fisheries that they represent.

Response: The text was modified to clarify that the only fishery for which incidental kill or injury was reported was the domestic Bering Sea groundfish trawl fishery. For additional information regarding fisheries interactions, the SAR references a complete list of fisheries and marine mammal interactions published annually by NMFS [67 FR 2410, January 17, 2002].

Comment 17: One commenter noted that the observer coverage for fisheries observer data was not stated.

Response: The range of observer coverage over the 5-year period (1996-2000), as well as the annual observed and estimated mortalities, are included in Table 2 of the SAR.Start Printed Page 62982

Comment 18: One commenter noted that the SAR states that most of the interactions involve walruses dead from other causes and recommended that the report provide information to support this statement.

Response: The text was modified to clarify that most of the observed interactions were with decomposed walrus carcasses or skeleton remains suggesting that the animals died prior to their interaction with the fishing gear.

Comment 19: One commenter noted that the SAR states that the rate of mortality and injury is estimated at “less than two animal [sic] per year,” but the basis of that estimate is not clear from the data presented.

Response: The SAR identifies the NMFS observer program as the source of information regarding fisheries interactions in U.S. waters. The range of observer coverage over the 5-year period (1996-2000), as well as the annual observed and estimated mortalities are included in Table 2.

Comment 20: One commenter recommended that the SAR should identify the potential indirect impacts that bottom trawling may have on the Pacific walrus population through alteration of habitat.

Response; Section 117(a)(4) of the Marine Mammal Protection Act states that stock assessments shall “describe commercial fisheries that interact with the stock.” We interpret this to mean those fisheries for which we have information about direct interactions with walrus, not fisheries with potential secondary impacts as suggested above.

Polar Bear Stock Assessment Reports

Chukchi/Bering Sea

Comment 21: One commenter questioned whether the process of delineating stocks is based on political reasons such as management agreements or evidence of significant biological distinction.

Response: We clarified the stock assessments for the Chukchi/Bering Seas stock and the Southern Beaufort Sea stock assessment to indicate that past and present management regimes have consistently distinguished between the Southern Beaufort Sea and Chukchi/Bering Seas stocks based upon biological evidence presented in the stock assessments.

Comment 22: Two commenters noted that the evidence suggesting that the stock has grown since 1972 was not sufficient to support the claims made regarding the trends in this population. This section also states that it is realistic to infer that the Chukchi/Bering Seas stock mimicked the growth pattern and later stability of the Beaufort Seas stock since that stocks have experienced similar management and harvest histories. However, this inference could be reasonably questioned for several reasons. First, growth patterns are a function of multiple factors including, but not limited to, harvest and management histories. As harvest and management histories are not the only determinants of growth trends, and as other possible factors (e.g., disease, shifts in distribution or availability of prey) are not evaluated, this inference should be questioned.

Response: We agree that scientific evidence is scant regarding population trends for the Chukchi/Bering Seas stock. Most of the evidence cited in sub-points a-e are from previous data should have not been reaffirmed in recent years. We have revised this section to indicate that, while evidence or impressions of population growth were appropriate previously, current data to support this conclusion is not available. For reasons stated earlier, it appeared reasonable to believe that the Chukchi/Bering Seas stock experienced growth following a 50% reduction in harvest in the 1970's and that population growth likely continued up to the early 1990s, similar to the Beaufort Sea stock. The Beaufort Sea stock stabilized in the 1990's. It is possible that the same may have been true for the Chukchi/Bering Seas stock, although this population was subject to additive unknown harvest levels, starting around 1992, that may have affected its status. Supporting evidence is not available to confirm the status of the population, and recent information regarding increased Russian harvest and decreased Alaska harvest are cause for concern. Consequently, we have chosen to designate the status of the Chukchi/Bering Seas stock as unknown.

Comment 23: One commenter noted that the harvest patterns for the two stocks may not have been the same. Subsistence harvests are illustrated in Figure 2 of each SAR, but comparisons should be done carefully as the y-axis is not the same in the two figures, and it appears that the number of bears taken from the Chukchi/Bering Seas stock may have been on the order of two times the number taken from the Southern Beaufort Sea stock. The significance of that difference will depend in part on the respective size of the two populations, and since the size of the Chukchi/Bering Seas stock is undetermined, the effects of harvesting are not clear.

Response: Figure 2 illustrates that the trend of declining U.S. harvests, post MMPA, were similar for both stocks. We acknowledge that the respective size of the two populations is crucial to understanding the effect of any harvest regime. Recent decline in harvest levels from the Alaska Chukchi/Bering Seas during the period 1996-2001 and reports of substantial illegal harvest in Russia are of concern. Because of these concerns, we revised the status of this stock to unknown.

Comment 24: One commenter noted that the report does not provide a basis for confidence in the precision and reliability of harvest estimates for Russian harvests.

Response: We have changed the Figure 2 caption to “Annual Alaska polar bear harvest from 1961-2001.” We have added text in the SAR to clarify that harvest estimates for Chukotka are based on anecdotal information.

Comment 25: Two commenters suggested that data for this stock continue to be insufficient for establishing a population estimate and urge the FWS to prioritize its research needs to improve the data available on this stock.

Response: The FWS has placed an emphasis on the development of the US/Russia Bilateral Treaty for the conservation of this population stock. The bilateral treaty includes provisions for conducting research to monitor population trends and develop population estimates for the Chukchi/Bering Seas stock. The current polar bear research program does not have adequate personnel or funding to conduct operations in both the Southern Beaufort Sea and the Chukchi/Bering Seas. The FWS continues to support implementation of the Bilateral Treaty, unified harvest management programs in Russia and Alaska, and conducting an aggressive polar bear research program to more effectively monitor this population.

Comment 26: One commenter noted that factors which may affect growth rates, including potential effects of global climate change and persistent organic pollutants were not included in the Southern Beaufort Sea stock assessment.

Response: We have incorporated these references into the Southern Beaufort Sea stock assessment.

Comment 27: One commenter recommended including the basis for the statement that the number of unreported kills since 1980 to the present time is thought to be negligible.

Response: We consider the number of unreported kills since 1980 to be negligible for the following reasons. All harvested bears in Alaska are required to have the skull and skin tagged through FWS's Marking, Tagging, and Start Printed Page 62983Reporting Program. Due to the relatively small number of bears taken; the high visibility, cultural importance, and sharing of the take within villages; the relatively large size and visible methods of handling polar bear hides; and repeated visits by biologists and reports from harvest monitors, we believe that the total harvest is accurately represented by the tagged and untagged bear harvest totals.

Comment 28: One commenter requested clarification on whether illegal hunting in Russia increased or became significant in 1992, and whether the occurrence of illegal hunting has been acknowledged since 1992.

Response: The text has been clarified to indicate that the occurrence and significance of illegal hunting was thought to have begun in 1992.

Comment 29: Two commenters noted that the basis for the statement that the “stock appears to be stable despite a substantial annual harvest” should be either justified with suitable evidence or deleted.

Response: For reasons previously stated, we have modified the text to acknowledge that the population status or trend of this population is unknown.

Comment 30: The draft stock assessment does not consider the impact of oil and gas development on polar bears as is done with the sea otter stocks.

Response: Oil and gas exploration or development projects have not been proposed in the Alaska Chukchi/Bering Seas during the past five years. If future oil and gas development projects are proposed, we will consider the potential effects to polar bears.

Southern Beaufort Sea

Comment 31: One commenter noted that it was not clear if estimates of the female, total, and minimum populations pertain to the entire period from 1986 to 1998, or perhaps only to the end of the period. Previous estimates by the same lead author suggested a doubling of size during the period from 1988 to 1998, although the report later suggests that the population is stable.

Response: We have condensed and clarified this information to indicate that Amstrup (unpublished data) estimated the total population to be 2,272. This population estimate for the period 1986-98 was based on an estimate of 1,250 females (CV = 0.17) and a sex ratio of 55% female from the best model (Amstrup et al. 2001). Nmin is 1,973 bears for a population size of 2,272 anc CV of 0.17.

Comment 32: In addition, it was not clear that the estimate of the minimum population is calculated correctly. The female population is estimated as 1,250 with a CV of 0.17. The total population is estimated by 1,250/0.55 and, based on the estimated minimum population, it appears that 0.55 was treated as a constant. Presumably, however, 0.55 is a correction factor that is also estimated with some degree of error, and that error should be included in the calculation of the CV for the total population estimate.

Response: A variance was not calculated for the 55% female sex composition and thus the ration is used as a constant for the abundance estimate. The Nmin estimate is correct, and typographic errors in the formula have been corrected.

Comment 33: One commenter suggested that the basis for the arguments that the population may have approached carrying capacity (K) was not evident based on the information provided. The report states that “the indication that the population was stable, births approximated deaths, is noteworthy.” It is unlikely that the data are available to confirm that births approximated deaths, so that statement appears to be a supposition. It is not clear what is meant by the statement that this supposition seems “noteworthy.” Clarification would be useful.

Response: The text has been revised to emphasize that the most recent population modeling exercise (Amstrup et al. 2001) suggests that the population grew during the late 1970's and 1980's and stablized in the 1990's. Inferences to the population relationship with carrying capacity have been removed. The statement that modeling indicates that the population stablized in the 1990's (Amstrup et al. 2001) is supported and has been retained as noteworthy since it indicates a change in status.

Comment 34: One commenter suggested that, without good juvenile survival estimates, life-history analysis and estimated growth rates may be inaccurate.

Response: Juvenile survival rates are not known for this population, nor well known for any polar bear population. We have good information on survival estimates of yearlings and two-year-old bears. Recently weaned two-year-old bears were assigned survival estimates of the two-year-old bears, and the three-year-old bears were given survival estimates of yearlings. We believe that these estimates are conservative.

Comment 35: The stock assessment for the Southern Beaufort Sea stock of polar bears notes that the potential biological removal level for this stock has been adjusted upward from 59 to 88 to account for the male harvest bias. For this stock, such an adjustment may be consistent with the purpose of PBR as set forth in the first sentence of the statutory definition (section 3 (20)), but is not consistent with the second part of the definition setting forth the formula for calculating PBR.

Response: In the narrative, PBR levels are calculated with and without a sex-biased harvest adjustment. We have chosen the adjusted PBR since it more accurately reflects what we would consider as a safe biological removal level. This is an issue of perception more than substance, since there is no application beyond taking of polar bears incidental to commercial fishing, and no incidental take of polar bears by commercial fisheries has occurred.

Comment 36: One found that the reported numbers of polar bear kills in the section on “Sport and native Subsistence Harvest” was confusing. A table of annual bear harvests by stock, time period, country, and type of hunt (sport versus subsistence) would help to clarify the history of harvest from this stock.

Response: We have reorganized and revised the text in this section and Figure 2 caption to clarify the harvest information. Figure 2 is included to illustrate a decline in the Alaska harvest after passage of the MMPA in 1972. The last five years of the Canada harvest data for the Southern Beaufort Sea stock have been summarized in the text.

Comment 37: One commenter noted that it was unclear as to whether the reference to industry pertains to the oil and gas industry specifically or all industry in general.

Response: The use of industry in the generic sense is correct in this sentence. While the incidental take regulations apply to the oil and gas industry, the statute allows U.S. citizens, including any industry, to petition for the development of incidental take regulations.

Literature Cited

Amstrup, S.C., T.L. McDonald, and I. Stirling. 2001. Polar bears in the Beaufort sea: A 30-year mark-recapture case history. Journal of Agricultural, Biological and Environmental Statistics. Vol 6(2):221-234.

Fay, F.H. J.J. Burns, S.W. Stoker, and J.S. Grundy. 1984. The struck-and-lost factor in Alaskan walrus harvests. Arctic 47(4):368-373.

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Dated: August 29, 2002.

David B. Allen,

Regional Director.

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[FR Doc. 02-25679 Filed 10-8-02; 8:45 am]