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    Southwest AlaskaDistinct PopulationSegment of theNorthern Sea Otter(Enhydra lutris kenyoni)

    Recovery Plan

    U.S. Fish & Wildlife Service

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    Southwest AlaskaDistinct Population Segment

    of the Northern Sea Otter(Enhyra lutris kenyoni)

    Recovery Plan

    *ULY 2013

    Prepared by

    Marine Mammals Management OfficeU.S. Fish and Wildlife Service

    for

    Region 7U.S. Fish and Wildlife Service

    Anchorage, Alaska

    Approved: ________________________________Regional Director, Region 7U.S. Fish and Wildlife Service

    Date: __________________________

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    iRecovery Plan

    Disclaimer

    Recovery plans delineate reasonable actions that are believed to be required to recover and/or protectlisted species. We, the U.S. Fish and Wildlife Service (FWS), publish recovery plans, sometimespreparing them with the assistance of recovery teams, contractors, State agencies, and others. Objectiveswill be attained and any necessary funds made available subject to budgetary and other constraintsaffecting the parties involved, as well as the need to address other priorities. Recovery plans do notnecessarily represent the views, official positions, or approval of any individuals or agencies involved inthe plan formulation, other than the FWS. They represent the FWS official position only after they havebeen signed by the Director or Regional Director as approved. Approved recovery plans are subjectto modification as dictated by new findings, changes in species status, and the completion of recoveryactions.

    Citation: U.S. Fish and Wildlife Service. 2013. Southwest Alaska Distinct Population Segment of theNorthern Sea Otter (Enhydra lutris kenyoni) - Recovery Plan. U.S. Fish and Wildlife Service, Region 7,Alaska. 171pp.

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    ii Southwest Alaska DPS of the Northern Sea Otter

    Recovery Team Members

    Lloyd Lowry - (Team Leader), University of Alaska FairbanksDouglas Burn - (Agency Lead), U.S. Fish and Wildlife ServiceLance Barrett -Lennard, University of British ColumbiaDavid Benton - Marine Conservation AllianceJames Bodkin - U.S. Geological SurveyKathleen Burek - Alaska Veterinary Pathology ServicesJim Curland - Defenders of WildlifeDouglas DeMaster - National Marine Fisheries ServiceJames Estes - U.S. Geological Survey (retired) and University of California, Santa CruzDick Jacobsen - Aleutians East BoroughKen Pitcher - Alaska Department of Fish and Game (retired)Katherine Ralls - Smithsonians National Zoological ParkMargaret Roberts - The Alaska Sea Otter and Steller Sea Lion Commission

    Tim Tinker - U.S. Geological Survey and University of California, Santa CruzKate Wynne - University of Alaska Sea Grant Program

    Acknowledgements

    The Recovery Team wishes to thank the following individuals who attended and participated in teammeetings: Greg Balogh, Leonard Corin, Angela Doroff, Verena Gill, Tracey Goldstein, Rowan Gould,Aaron Haines, Charles Hamilton, Lianna Jack, Judy Jacobs, Sonja Jahrsdoerfer, Karen Laing, EllenLance, Rosa Meehan, Karen Oakley, Alvin Osterback, Peggy Osterback, Leslie Slater, Robert Small,Kristine Sowl, Charla Sterne, Ted Swem, Doug Vincent-Lang, Jeff Williams, and Bill Wilson. TheTeam also thanks Melissa Miller, Tracey Goldstein, and Stephen Raverty for providing unpublishedinformation about diseases in sea otters, and Dana Jenski, Angela Doroff, and Verena Gill for assistance

    with recording minutes during Team meetings. Rose Primmer provided technical support for both thepublic and internal Team web pages. Ellen Baier coordinated travel arrangements for out-of-town Teammembers. The North Pacific Research Board graciously provided space for Team meetings. RandyReeves provided a thorough review of the Teams draft plan, and we thank him for his helpful commentsand suggestions. Rosa Meehan , Sonja Jahrsdoerfer, Frances Mann, and Suzann Speckman providedadditional review and comments on the draft plan.

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    iiiRecovery Plan

    Executive Summary

    Based on survey information that indicated thatthe southwest Alaska population of northern seaotters (Enhydra lutris kenyoni) had declinedin abundance by more than 50% since the mid-1980s, the U.S. Fish and Wildlife Service (FWS)listed this distinct population segment (DPS)as threatened in August 2005. Section 4(f) ofthe Endangered Species Act (ESA) directs theSecretary of the Interior to develop and implementplans (generally known as recovery plans) forthe conservation and survival of endangeredspecies and threatened species. In March 2006,the Regional Director for the Alaska Region of

    the FWS formed a recovery team to serve in anadvisory capacity to develop a draft recovery planfor the southwest Alaska DPS of the northern seaotter.

    The sea otter is the largest species in the mustelidfamily, and one of the smallest marine mammals. Itpossesses a number of unique adaptations allowingit to exist in the nearshore marine environment.As the only marine mammal species that lacks ablubber layer, the sea otter relies on a dense coatof fur as insulation from the cold waters whereit occurs. To maintain the insulative propertiesof their fur, sea otters must groom themselves

    regularly. Their reliance on fur for insulation alsomakes them highly vulnerable to oil spills. Inaddition to using fur for insulation, sea otters havea relatively high metabolic rate that helps themmaintain their body temperature. This requiresthem to consume large quantities of prey, as muchas 20-33% of their body weight per day. Withfew exceptions, sea otter prey consists of benthicinvertebrates. Sea otter habitat is partially definedby physiological limitations in diving depth, and theanimals generally occur in or near shallow waters.

    The discovery of large sea otter populations inAlaska by the Russian Bering expedition in 1741

    resulted in a commercial fur harvest that lasted170 years and extirpated sea otters from much oftheir historic range. When the species was finallygiven protection under the International Fur SealTreaty of 1911, the worldwide population mayhave consisted of fewer than 1,000 individuals in13 remnant colonies. Throughout much of the20th century, these remnant colonies grew andexpanded their range, eventually recolonizingmuch of the species historically occupied habitat.In the late 1960s and early 1970s, the process ofrecolonization was enhanced by the translocationof otters from areas of high abundance to sites

    from which they had been extirpated by the furharvest. During the 1990s, sea otter surveys in theAleutian archipelago indicated that the populationtrend had shifted from growth and expansion todecline. Additional surveys throughout southwestAlaska helped define the scope and magnitude ofthe population decline, which led eventually to thelisting of this DPS as threatened.

    The southwest Alaska DPS ranges from west toeast across more than 1,500 miles of shoreline, andthe otters occur in a number of distinct habitattypes. The magnitude of the population decline

    has varied over the range. In some areas, numbershave declined by more than an order of magnitude,while in other areas no decline has been detected.To address such differences, this recovery planidentifies five management units (MUs) withinthe DPS: 1) Western Aleutian Islands; 2) EasternAleutian Islands; 3) South Alaska Peninsula; 4)Bristol Bay; and 5) Kodiak, Kamishak, AlaskaPeninsula.

    The cause of the overall decline is not knownwith certainty, but the weight of evidence pointsto increased predation, most likely by the killerwhale (Orcinus orca), as the most likely cause.

    Predation is therefore considered a threat to therecovery of this DPS, but other threats, includinginfectious disease, biotoxins, contaminants, oilspills, food limitation, disturbance, bycatch infisheries, subsistence harvest, loss of habitat, andillegal take, are also considered in this recoveryplan. Threats are summarized in general, andtheir relative importance is assessed for each ofthe five MUs. Most threats are assessed to beof low importance to recovery of the DPS; thethreats judged to be most important are predation(moderate to high importance) and oil spills (low tomoderate importance). Threats from subsistenceharvest, illegal take, and infectious disease are

    assessed to be of moderate importance in theKodiak, Kamishak, Alaska Peninsula MU, but oflow importance elsewhere.

    The goal of the recovery program is to control orreduce threats to the southwest Alaska DPS ofthe northern sea otter to the extent that this DPSno longer requires the protections afforded by theESA and therefore can be delisted. To achieve thisgoal, the recovery plan identifies three objectives:1) achieve and maintain a self-sustaining populationof sea otters in each MU; 2) maintain enough seaotters to ensure that they are playing a functional

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    iv Southwest Alaska DPS of the Northern Sea Otter

    role in their nearshore ecosystem; and 3) mitigatethreats sufficiently to ensure persistence of seaotters. Each of these objectives includes explicitcriteria to determine if the objective has beenmet; these are known as delisting criteria. Theystipulate that in order for the DPS to be removedfrom the Endangered and Threatened Species List,at least three of the five MUs must have met thedelisting criteria. The plan also contains criteriato determine if the DPS should be considered for

    reclassification as endangered; these are knownas uplisting criteria. Delisting should not beconsidered if any MU meets the criteria specifiedfor uplisting to endangered.

    Specific actions to achieve recovery and delistingof the DPS are specified in the recoveryaction outline and narrative. As demographiccharacteristics of the population constitute oneof the three types of delisting criteria, populationmonitoring and population modeling are highpriorities. Monitoring the status of the kelpforest ecosystem in the Western Aleutian andEastern Aleutian MUs is also a high priority, as

    results from such monitoring will be needed toevaluate the ecosystem-based delisting criteria.Other high-priority actions include identifyingcharacteristics of sea otter habitat, and ensuringthat adequate oil spill response capability existsin southwest Alaska. As predation is consideredto be the most important threat to recovery,additional research on that topic is also a highpriority. The recovery implementation scheduleprovides details regarding the timing, costs, andagencies or entities responsible for implementingeach recovery action. The full cost of implementingthis recovery plan over the next five years isapproximately $15M, of which $2.815M is for

    Priority 1 actions. Securing adequate funding toimplement the plan is therefore also a high priority.

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    vRecovery Plan

    Table of Contents

    Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

    Recovery Team Members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

    Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

    Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

    List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .vii

    List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

    List of Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

    1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1A. Brief history of listing and recovery planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1B. Ecosystem context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

    2. Biological Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1A. Species description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1B. Morphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2C. Physiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4D. Distribution and habitat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4E. Population biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5F. Behavior. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7G. Foraging ecology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9H. Population history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

    I. Population abundance and trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

    3. Threats and Impediments to Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1A. Predation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1B. Infectious diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5C. Biotoxins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17D. Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17E. Oil spills and oiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-19F. Food limitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21G. Disturbance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27H. Bycatch and entanglement in debris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27I. Subsistence harvest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-29J. Habitat concerns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30K. Illegal take . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-34

    4. Threats Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

    5. Recovery Strategy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

    NOTE: this recovery plan is paginated by section, which will allow individual sections of the plan to beupdated without requiring the entire document to be reprinted.

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    6. Recovery Goals, Objectives, and Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1A. Recovery Goal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1B. Recovery Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1C. Criteria for delisting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1D. Criteria for reclassification to endangered (uplisting) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4E. Summary of demographic status in relation to delisting and uplisting criteria . . . . . . . . . . . . . . . 6-5

    7. Recovery Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1A. Recovery Action Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1B. Recovery Action Narrative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

    8. Implementation Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1A. Key to Responsible Agencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1B. Recovery Implementation Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2

    9. Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1A. Print Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1B. Personal Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-16

    Appendix A. Ecosystem-based Recovery Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

    A p p e n d i x B . P o p u l a t i o n V i a b i l i t y A n a l y s i s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-1

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    viiRecovery Plan

    Table 1. Recent sea otter population estimates for MUs within the southwest Alaska DPSof the northern sea otter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23

    Table 2. Occurrence of major known diseases and disease agents in sea otters bygeographic region.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7

    Table 3. Information on disease agents investigated in sea otters in the Gulf of Alaska andthe Aleutian Islands.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13

    Table 4. Information on biotoxins found in sea otters in the Gulf of Alaska and theAleutian Islands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

    Table 5. Information on contaminants found in sea otters in the Gulf of Alaska and the

    Aleutian Islands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20

    Table 6. Summary of reported non-crude oil spills in southwest Alaska by MU,July 1, 1995 June 30, 2005.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-23

    Table 7. Reported sea otter subsistence harvest in Alaska, 1989-2008. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-31

    Table 8. Age and sex composition of the reported sea otter subsistence harvest from thesouthwest Alaska DPS of the northern sea otter, 1989-2008. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-32

    Table 9. Reported subsistence harvest of sea otters from the southwest Alaska DPS ofthe northern sea otter by MU, 1989-2008.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-33

    Table 10. Threats analysis for the Western Aleutian Islands MU of the southwest Alaska

    DPS of the northern sea otter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

    Table 11. Threats analysis for the Eastern Aleutian Islands MU of the southwest AlaskaDPS of the northern sea otter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

    Table 12. Threats analysis for the Bristol Bay MU of the southwest Alaska DPS of thenorthern sea otter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

    Table 13. Threats analysis for the South Alaska Peninsula MU of the southwest AlaskaDPS of the northern sea otter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

    Table 14. Threats analysis for the Kodiak, Kamishak, Alaska Peninsula MU of thesouthwest Alaska DPS of the northern sea otter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

    Table 15. Summary of importance of threats to recovery of the southwest Alaska DPS ofthe northern sea otter by management unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

    Table 16. Estimates of available habitat, equilibrium density, and carrying capacity forthe five management units in the southwest Alaska DPS of the northern sea otter.. . . . . . . . . . . . . . . . . . 6-3

    Table 17. Summary of criteria that must be met prior to delisting the southwest AlaskaDPS of the Northern sea otter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

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    Table 18. Examples of estimates that are developed by PVA models using available data through 2007.Estimates shown include carrying capacity, delisting abundance, uplisting abundance, and current statusrelative to carrying capacity for each of the five management units in the southwest Alaska DPS of thenorthern sea otter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5

    Table A-1. Summary of the datasets used to examine the relationship between sea otterdensity and sea urchin biomass in the Aleutian Islands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-8

    Table B-1. Projection matrix used in population model to calculate demographic transitions(survival and reproduction) occurring between year t and year t+1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-10

    Table B-2. Vital rate estimates used to parameterize the projection matrix (Table B-1) forsea otter populations at low density and high density (at K) situations. . . . . . . . . . . . . . . . . . . . . . . . . . B-11

    Table B-3. Estimates (based on expert opinion of the Recovery Team) of the number ofsea otters dispersing from a source population on one island to a remote population onanother island, as a function of the density relative to carrying capacity at the sourcepopulation, and the distance between the two islands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-11

    Table B-4. Time series of skiff survey counts of sea otters (excluding dependent pups) forseven islands in the Aleutian archipelago between 1991 and 2007. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-12

    Table B-5. Alternate functional forms evaluated for modeling , the per-capita rate ofage-independent mortality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-13

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    Figure 1. Present distribution of three subspecies of sea otters (hatched areas).. . . . . . . . . . . . . . . . . . . . 2-2

    Figure 2. Northern sea otter stock boundaries in Alaska, from Gorbics and Bodkin (2001).. . . . . . . . . . . 2-3

    Figure 3. Management units for the southwest Alaska DPS of the northern sea otter.. . . . . . . . . . . . . . 2-13

    Figure 4. Western Aleutian Management Unit (WA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14

    Figure 5. Sea otter survey results for the Near Island group. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14

    Figure 6. Sea otter survey results for the Rat Island group. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-15

    Figure 7. Sea otter survey results for the Andreanof Island group. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-16

    Figure 8. Eastern Aleutian Management Unit (EA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-16

    Figure 9. Sea otter survey results for the Eastern Aleutian MU. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-17

    Figure 10. Bristol Bay Management Unit (BB). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-17

    Figure 11. Sea otter survey results for the Bristol Bay MU. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19

    Figure 12. South Alaska Peninsula Management Unit (SAP). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19

    Figure 13. Sea otter survey results for the South Alaska Peninsula MU. . . . . . . . . . . . . . . . . . . . . . . . . 2-20

    Figure 14. Kodiak, Kamishak, Alaska Peninsula Management Unit (KKAP). . . . . . . . . . . . . . . . . . . . . . 2-21

    Figure 15. Sea otter survey results for the Kodiak, Kamishak, Alaska Peninsula MU.. . . . . . . . . . . . . . 2-22

    Figure A-1. Published data on kelp density vs. sea urchin biomass from islands in theAleutian archipelago at which otters were abundant (Adak and Amchitka) or absent(Alaid, Nizki, Shemya). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-9

    Figure A-2. Available data on kelp density vs. urchin biomass from the Aleutianarchipelago, obtained from 19 islands sampled at various times between 1987 and 2006. . . . . . . . . . . . . A-10

    Figure A-3. Data from Figure A-2, averaged by island/year combination. . . . . . . . . . . . . . . . . . . . . . . . . A-11

    Figure A-4. Canonical discriminant function fit to database of kelp density vs. sea urchinbiomass from the 34 island/year combinations currently available from the Aleutian

    archipelago (see Table A-1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-12

    Figure A-5. Logistic regression of ecosystem phase state vs. sea otter density (usingskiff surveys) as determined by data from 17 island/year combinations. . . . . . . . . . . . . . . . . . . . . . . . . . . A-13

    Figure A-6. Sampling intensity vs. statistical power in correctly classifying ecosystemphase state. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-14

    Figure B-1. Theta-logistic population growth typical of sea otter populations. . . . . . . . . . . . . . . . . . . . . . B-14

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    Figure B-2. Smoothed, age-specific vital rate estimates calculated for two sea otterpopulations, one at low density (parameterized from sea otters at Kodiak Island) and oneat high density, near K (parameterized from sea otters at Amchitka Island). . . . . . . . . . . . . . . . . . . . . . . B-15

    Figure B-3. Estimated average rates of inter-island dispersal (expressed as percentage ofthe source population dispersing) under two scenarios: A) a low dispersal scenario, andB) a high dispersal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-16

    Figure B-4. Examples of weighting functions used to randomly select values of t, whichwere then used to generate values of age-independent mortality, (D,t), in simulations of

    future population dynamics in southwest Alaska sea otters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-17

    Figure B-5. Sample results from the maximum-likelihood fitting of age-independentmortality () to observed skiff counts (Nobs). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-18

    Figure B-6. Relative degree of support for nine different functional forms used to model ,the per-capita rate of age-independent mortality, as measured by maximum-likelihoodAIC weights (higher AIC weights indicate greater support for a given functional form). . . . . . . . . . . . B-19

    Figure B-7. Best-fit values of, the per-capita rate of age-independent mortality, plottedas a function of time (t) and relative population density (D). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-20

    Figure B-8. Sample simulation results from the PVA model projections. . . . . . . . . . . . . . . . . . . . . . . . . . B-21

    Figure B-9. PVA model results for the western Aleutian management unit. . . . . . . . . . . . . . . . . . . . . . . B-22

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    List of Acronyms

    CDV canine distemper virusDDT dichlorodiphenyltrichloroethaneDMV dolphin morbillivirusDPS distinct population segmentESA Endangered Species ActFWS U.S. Fish and Wildlife ServiceGPS global positioning systemHAB harmful algal bloomMHC major histocompatibility complexMMM Marine Mammals ManagementMMPA Marine Mammal Protection ActmtDNA mitochondrial DNAMTRP marine mammal marking, tagging, and reporting program

    MU management unitNMFS National Marine Fisheries ServiceOC organochlorineOLE Office of Law EnforcementPCB polychlorinated biphenylPCR polymerase chain reactionPDV phocine distemper virusPFCs perfluorinated compoundsPMV porpoise morbillivirusPOP persistent organic pollutantPSP paralytic shellfish poisonPVA population viability analysisPWS Prince William SoundTDR time-depth recorder

    UME unusual mortality eventUSGS U.S. Geological SurveyVE valvular endocarditisVHF very high frequency

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    1. Introduction

    actions relating to currently planned and futuredevelopment activities. Recovery planning isdynamic, and a recovery program, including therecovery actions, will be reviewed periodicallyas new information becomes available. Asappropriate, recovery plans are amended to reflectnew information or a change in strategy.

    Recovery plans identify site-specific managementactions that, if completed, could lead toreclassification to a less critical status or helpthem recover to the point they can be removedfrom ESA protection. The ESA clearly envisions

    recovery plans as the central organizing tool forguiding each species recovery process. Theyshould also guide Federal agencies in fulfillingtheir obligations under section 7(a)(1) of the ESA,which calls on all Federal agencies to utilize theirauthorities in furtherance of the purposes of thisAct by carrying out programs for the conservationof endangered species and threatened species...As a result of these efforts, the ESA has beencredited with saving species such as the Californiacondor, black-footed ferret, peregrine falcon,and our Nations symbol, the bald eagle, fromextinction.

    B. Ecosystem context

    Species often have strong influences on theirassociated ecosystems. The effects can occur invarious ways. In some cases, the effect is self-evident, based on sheer numbers, as for examplewith a dominant tree species in a forest. Numericaldominants may influence other species throughcompetition for limited resources; by affectingfeatures of the physical environment such aslight intensity, temperature, wind, and moisture;through the provision of habitat; or by controllingthe flux of energy and matter through theecosystem.

    Comparatively rare species can also play importantecological roles, in some cases having landscape-level effects on the ecosystem that rival or exceedthose of numerical dominants. This occurs undertwo conditionseither when per capita interactionstrength with one or more other species is high(Paine 1992, Berlow et al. 1999) or when thesedirect interactions penetrate the ecosystemsinteraction web through indirect effects so as toinfluence other species and ecosystem processes.Comparatively rare but ecologically importantspecies have been referred to as keystone species(Paine 1969, Power et al. 1996). Keystone species

    A. Brief history of listing and recovery

    planning

    In April 2000, the U.S. Fish and Wildlife Service(FWS) conducted an aerial survey of sea otters(Enhydra lutris) in the Aleutian archipelago. Theresults of that survey indicated that the populationthere had declined by an estimated 70% since 1992,which prompted the FWS to designate otterswithin that portion of their range as a candidatespecies for listing under the U.S. EndangeredSpecies Act (ESA). Additional aerial surveysrevealed that the decline extended beyond theAleutians, and included much of the southwestAlaska population of northern sea otters (the

    region extending from the west side of Cook Inletto Attu Island at the western end of the Aleutians,including Kodiak Island and Bristol Bay).

    On 11 February 2004, FWS published a proposedrule (69 FR 6600) to list the northern sea otterin southwest Alaska as a threatened distinctpopulation segment (DPS). The ESA definesthreatened as likely to become endangeredin the foreseeable future over all or a significantportion of its range. The ESA also definesendangered as likely to become extinct over allor a significant portion of its range. Following a120-day public comment period, the FWS published

    a final rule (70 FR 46366) on 9 August 2005, listingthe DPS as threatened.

    The recovery planning process for the southwestAlaska DPS of the northern sea otter beganin 2006, when the recovery team was formed.Collaborative efforts are critical to recoverysuccess, and therefore, the recovery team wascomprised of 15 people representing Federal andState agencies, universities, Tribal government,The Alaska Sea Otter and Steller Sea LionCommission, and conservation organizations.Recovery plans are developed and implementedby the Service and our partners to help increase

    species populations and manage the threats totheir existence. Comments on the draft recoveryplan for the southwest Alaska DPS of the northernsea otter were solicited from the general public andfrom known interested groups, including AlaskaNative Organizations and the State of Alaska.

    It is important to recognize that recovery plans areguidance documents, not regulatory documents.No agency or entity is required by the ESA toimplement the recovery strategy or to adhere tospecific actions in a recovery plan. For example,recovery plans do not dictate any particular

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    often are apex predators and their ecosystem-level effects frequently play out through whathave become known as trophic cascades1 (Paine1980, Carpenter and Kitchell 1993). Both keystonespecies and trophic cascades are known to occur inmany ecosystems (Pace et al. 1999).

    Where they inhabit areas with rocky substrates(which includes much of the range of the southwestAlaska DPS), sea otters provide a widely known

    and well-documented example of a keystonespecies. The ecosystem-level effects in this caseoccur through a simple food chain involving seaotters, sea urchins, and kelp. Sea urchins areamong the most frequently consumed prey ofsea otters, and when sea otters are sufficientlyabundant they are capable of limiting sea urchinnumbers and biomass. Sea urchins consume kelpand other macroalgae, and when sufficientlyabundant are capable of preventing kelp forestsfrom becoming established in extensive areasof shallow rocky reef habitat. These consumer-prey interactions act together to define a trophiccascade, such that sea otters protect kelp forests

    from destructive overgrazing (Estes and Palmisano1974, Estes and Duggins 1995). Like forests onland, kelp forests exert important effects onnumerous other species and ecosystem-levelprocesses (see Appendix A).

    The recent population decline of sea otters insouthwest Alaskas Aleutian archipelago hasresulted in a wholesale phase shift in the coastalecosystem from kelp forests to deforested seaurchin barrens (Estes et al. 1998, Estes et al.2004, Estes et al. 2010). In view of the sea otterskeystone role in coastal marine ecosystems, thegoal of recovery must be not only to assure thecontinued survival of sea otters, but also to assurethat they are numerous enough to maintain kelpforests through the otter-urchin-kelp trophiccascade. In other words, the objectives of recoveryare not only to achieve a demographically viablepopulation, but also to achieve an ecologicallyeffective (sensu Soul et al. 2003, Soul et al. 2004)sea otter population density.

    1 Trophic cascades occur when predators in a foodweb suppress the abundance of their prey, therebyreleasing the next lower trophic level from preda-tion (or herbivory if the intermediate trophic levelis an herbivore).

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    2. Biological Background

    For nearly 50 years the United States Departmentof the Interior (specifically the FWS and U.S.Geological Survey (USGS)) has supported aresearch program directed at describing andunderstanding the natural history of sea otters.Research on both wild and captive sea ottershas also been supported by the governments ofRussia, Canada, and Japan, the state governmentsof Alaska, California, and Washington, andnumerous academic institutions, aquaria, andnon-governmental organizations. The scope ofresearch has been broad and multi-dimensional,but with a focus generally directed toward: 1)

    understanding basic biology, particularly as itrelates to conservation of the species; 2) supportof translocations from remnant populationsto unoccupied habitats in California, Oregon,Washington, British Columbia, and southeastAlaska; 3) understanding and describing the roleof sea otters as keystone predators in structuringnearshore marine communities; 4) describingrelations between human uses of nearshore marineresources and sea otters; 5) defining threats to seaotter recovery from human activities, particularlythe effects of spilled oil; and 6) understanding thefactors responsible for, or contributing to, changesin sea otter populations.

    Following the Bering expedition of 1741, seaotters were nearly extirpated for their furby both Russians and Americans. After theInternational Fur Seal Treaty of 1911 protectedsea otters from further commercial exploitation,sea otter populations generally displayed positivegrowth rates throughout most of the 20th century(although rates varied among populations), andrange expansion along with translocations resultedin recolonization of some previously occupiedhabitat. The spatial pattern of occupied andunoccupied habitat and the variation in temporalpatterns of sea otter recovery enabled comparisons

    of populations at various stages of recovery, andcomparisons of habitats both with and withoutsea otters. As a result of the long-term dedicatedresearch on this species, and the ability to makeexperimental comparisons owing to the patternsof sea otter presence and absence, a rich, diverse,and extensive body of literature exists on sea otterbiology and ecology. Researchers will be able todraw on this foundation of knowledge as they seekto address unanswered and emerging questionsin order to further aid sea otter conservation.While this document includes basic backgroundinformation on the sea otter, it emphasizes those

    aspects of biology and ecology most likely to berelevant to the conservation of the southwestAlaska population. Other aspects of the speciesbiology and ecology have been reviewed byKenyon (1969), VanBlaricom (1988), Riedman andEstes (1990), and Estes and Bodkin (2002), and aredescribed in other references listed in Section 9 ofthis plan.

    A. Species description

    The sea otter is a mammal in the order Carnivora.It is the only completely marine species of the

    aquatic Lutrinae, or otter subfamily of the familyMustelidae (skunks, weasels, minks, badgers,and honey badgers) (Wozencraft 1993). Basedon nucleotide sequences of the mitochondrialcytochrome b gene, Koepfli and Wayne (1998)placed Enhydra in one of three reorganized lutrineclades (a group of biological taxa or species thatshare features inherited from a common ancestor).Two lineages of sea otter are recognized. Oneled to the extinct Enhydriodon; the other toEnhydritherium and subsequently to Enhydra(Berta and Morgan 1986). Early specimens ofEnhydra, dating to the early Pleistocene, 1-3million years ago, have been found along the

    Pacific Rim and the genus apparently has remainedconfined to that basin (Riedman and Estes 1990).

    Early sea otter taxonomy below the specieslevel was based primarily on comparison of skullmorphology between sea otters from Alaskaand California. After an exhaustive systematicreview and analysis of skull morphology, Wilsonet al. (1991) concluded there are three subspecies,E. lutris lutris from Asia to the CommanderIslands, E. l. nereis from California, and E. l.kenyoni from Alaska (Figure 1). This taxonomyis largely supported by subsequent moleculargenetic data. Analysis of mitochondrial DNA

    (mtDNA) variation among eight geographicallyisolated populations identified four major groups(Cronin et al. 1996, Scribner et al. 1997). However,the haplotype frequency (genetic pattern) in theCommander Islands population ofE. l. lutris ismore similar to that observed in the Aleutian-Kodiak grouping, E. l. kenyoni, than to the Asiansubspecies, E. l. lutris, with which it was alignedby skull morphology. Additionally, the PrinceWilliam Sound (PWS) population differs from otherAlaska populations in haplotype frequency. Thedistribution of mtDNA haplotypes suggests littleor no recent female-mediated gene flow among

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    populations sampled. However, populationsseparated by large geographic distances sharedsome haplotypes (e.g., the Kuril Islands and KodiakIsland), suggestive of common ancestry and somelevel of historic gene flow. In a review of sea

    otter studies using genetic markers, Scribner etal. (1997) concluded that populations are highlydifferentiated genetically, although limitedsequence divergence and lack of phylogeographicconcordance suggest an evolutionarily recentcommon ancestor and some degree of gene flowthroughout the range. The differences seen ingenetic markers among contemporary sea otterpopulations likely reflect periods of habitatfragmentation and consolidation during Pleistoceneglacial advance and retreat, effects of limitedgene flow resulting from natural geographicbarriers and limited dispersal capability, andthe recent history of harvest-related reductions

    and subsequent recolonization. The populationbottlenecks that resulted from the fur tradeharvest may have caused a significant loss ofgenetic diversity, similar in magnitude to theloss in other species with similar recent histories(Ralls et al. 1983, Larson et al. 2002a, Larsonet al. 2002b), and this could reduce long-termpopulation viability. However, Aguilar et al. (2008)concluded that the bottleneck and subsequentloss of genetic diversity in the California sea otterpopulation occurred prior to the onset of the furtrade. Genetic diversity is higher in translocatedpopulations that came from two source populations(e.g., southeast Alaska and British Columbia)

    than in a population that originated from a singlesource population (Washington; Larson et al.2002a). Despite the potential for reduced fitnessresulting from population bottlenecks and reducedgenetic diversity, rates of increase for translocated

    populations are significantly higher than those forremnant populations (Bodkin et al. 1999).

    Currently, FWS recognizes three stocks of seaotters in Alaska: southeast Alaska, southcentralAlaska, and southwest Alaska (Gorbics and Bodkin2001; Figure 2). Available data on movements andhome ranges of sea otters and findings of divergentpopulation trends at relatively small spatial scales(Bodkin et al. 2002) are suggestive of populationstructuring at smaller geographic scales thanpresently recognized.

    B. Morphology

    The sea otter is the largest mustelid. Adult malesattain weights of 45 kg and total lengths of 148 cmand adult females attain weights of 36 kg and totallengths of 140 cm. Size appears to vary amongpopulations and to a large extent may reflect thestatus of the population relative to available foodresources. Weights reported from populationsbelow equilibrium density exceed those frompopulations at or near equilibrium density by 28%for males and 16% for females (Kenyon 1969).At Bering Island, Russia, mean weights of adultmale sea otters declined from 32.1 kg in 1980to 25.1 in 1990, coinciding with the population

    Figure 1. Present distribution of three subspecies of sea otters (hatched areas).

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    exceeding carrying capacity and a 41% reduction inpopulation size (Bodkin et al. 2000). In California,otters in a small, translocated population at SanNicolas Island (where food is abundant) aresignificantly larger than otters in the source

    population (where food is limiting): female mass is31% greater and male mass is 35% greater (Bentall2005). At birth, pups weigh 1.7-2.3 kg and are about60 cm in total length.

    The sea otter skull is broad and blunt and withdentition (teeth) that differs from that of mostother carnivores in being adapted to crush prey,as opposed to shearing. The canines are long,rounded, and blunt, and used to puncture andpry open prey. The molars are broad and flat,with rounded crowns effective in grinding. Theincisors and canines are used to scrape tissues outof shelled prey. A vestigial premolar is present

    and can be used to estimate age based on annualdeposits of cementum (Bodkin et al. 1997). Dentalproblems associated with tooth wear and breakageleading to systemic infection may be a commoncontributing cause of mortality, particularly in oldindividuals (Kenyon 1969).

    Fur and the air trapped within it provide theprimary sources of insulation and buoyancy forthe sea otter. In contrast to most other marinemammals (which rely on blubber for insulation),sea otters have little or no sub-cutaneous fat. Thepelage (fur) consists of relatively sparse outerguard hairs and a shorter, very dense underfur at

    a ratio of about 1:70. Hair densities range fromnearly 26,000/cm2 on the hind flipper to 65,000/cm2on the foreleg (Williams et al. 1988). Sebaceousglands secrete oil that aids in water repulsion. Theabsence of arrector pili muscles in the epidermis

    permits the guard hairs to lie nearly parallel tothe skin, and this allows the underfur to remaindry even when submerged in water. The abilityof the sea otter to thermoregulate is dependenton maintaining the integrity of the pelage, inconjunction with an extremely high metabolicrate. This requires a nearly constant, yet gradual,molt, as well as frequent and vigorous grooming.The color of the pelage ranges from light brown tonearly black. As animals age, they may attain agrizzled appearance, with whitening occurring inthe head, neck, and torso regions. Newborn pupshave a pale brown, woolly natal pelage until aboutthree months of age.

    The forelegs of the sea otter are short and powerfulwith sensitive paws and extrudable claws usedto locate, acquire, and manipulate prey. Forelegsare not used in propulsion. A fold of skin at theaxilla (armpit) of each forelimb is used to storeand transport prey gathered while foraging. Preyorganisms are always consumed at the surface,where they are held and manipulated with theforepaws. The sea otter is one of the few non-human species known to use tools, often usingrocks or shells as anvils or hammers to break openhard-shelled prey. The hind limbs are flattenedand flipper-like. While swimming, the posterior

    Figure 2. Northern sea otter stock boundaries in Alaska, from Gorbics and Bodkin (2001).

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    margins of the hind flippers approximate thelunate (crescent-shaped) pattern and undulatingmovement of the flukes of cetaceans (whales,dolphins, and porpoises). The tail is long,horizontally flattened, and used in swimming,particularly during slow movements while on thesurface. The ears are short and usually held erectwhile at the surface. While diving, the ears areheld downward, presumably to exclude water.Rapid swimming occurs in a face-down position

    and generally includes diving and may includeporpoising for brief periods. Slower swimminggenerally occurs with the otter on its back withpropulsion provided by the hind flippers and/or tail.

    C. Physiology

    The general mammalian problem of maintaininga constant and elevated body temperature isexacerbated in the sea otter because of its smallbody size (relative to other marine mammals)and the resulting high surface to volume ratio, aswell as the generally cold water temperatures ofhigh-latitude marine environments. The sea otter

    appears to be one of the few mammals to exist inambient temperatures outside its thermal-neutralzone (Yeates 2006). In addition to using air in thepelage as an external insulator to reduce heatloss, metabolic heat production in the sea otteris 2.43.2 times that predicted in a terrestrialmammal of similar size (Costa and Kooyman 1982).To maintain an average body temperature of about38 C, a standard metabolic rate of about 0.72 cm3O2/gm body weight/hour has been measured inthe sea otter (Morrison et al. 1974). To maintainthe elevated metabolic rate, energy intake mustalso be elevated, requiring consumption of preyequal to about 20-33% of body weight per day

    (Kenyon 1969, Costa 1982). Although the airlayer in the fur is an efficient insulator, it is alsoinflexible, requiring a mechanism to dissipate heatduring periods of intense exercise. This appearsto be accomplished through the broad, highlyvascularized, sparsely furred hind flippers.

    Some of the physiological adaptations evident insea otters result from their residing solely in a salt-water environment and foraging under hyperbaric(pressurized) conditions. Sea otters have littleaccess to fresh water and feed primarily on marineinvertebrates that are isotonic with seawaterand may contain relatively high concentrations

    of nitrogen, iodine, and other electrolytes. Theotters are able to cope with these conditions byconsuming sea water (thereby increasing theirurinary osmotic space) and producing largevolumes of moderately concentrated urine fromlarge, highly efficient kidneys (Costa 1982). Thelungs are nearly 2.5 times larger than in othersimilar-sized mammals, serving to store oxygenneeded for diving and buoyancy (Costa andKooyman 1982). Oxygen-hemoglobin affinity isrelatively high, thus increasing blood-oxygenstorage capacity. Hemoglobin, red blood cell,and hematocrit values in sea otters are similar to

    values in pinnipeds (seals, sea lions, and walruses)and cetaceans (Bossart and Dierauf 1990). Thetrachea is relatively wide compared to other otters,allowing rapid and complete air replacementbetween dives.

    D. Distribution and habitat

    The sea otter occurs only in the North PacificOcean, and its historical range includes coastal

    habitats around the Pacific rim between centralBaja California and northern Japan. The rangecurrently occupied extends from southernCalifornia to northern Japan, with extralimitalsightings in central Baja California and nearWrangel Island in the Chukchi Sea. The northwardlimits in distribution appear related to the southernlimits of sea ice, which can preclude access toforaging habitat. Seasonal and inter-annualvariation in the southern extent of sea ice resultsin constriction and expansion of the sea ottersnorthern range. During periods of advancingwinter sea ice along their northern range, seaotters occasionally become trapped and sometimes

    die (Nikolaev 1965, Schneider and Faro 1975). Seaotters attempting to travel tens of kilometers overthe Alaska Peninsula to gain access to the ice-freePacific were observed in 1971 and 1972 (Schneiderand Faro 1975) and again in 1982, 1999, and 2000(USGS unpublished data). Although some ottersmay succeed in such efforts, many apparently diefrom starvation or predation by wolves (Canislupus), red foxes (Vulpes vulpes), and wolverines(Gulo gulo). Southern range limits are lesswell understood but appear to coincide with thesouthern limits of coastal upwelling, associatedcanopy-forming kelp forests, and the 20-22 C seasurface isotherm (Kenyon 1969).

    Sea otters occupy and use all coastal marinehabitats within their range, from protected baysand estuaries to exposed outer coasts and offshoreislands. Because they need to dive to the seafloor to forage (Bodkin 2001), the seaward limit oftheir usual distribution is defined by their divingability and is approximated by the 100 m depthcontour. While sea otters can be found at thesurface in water deeper than 100 m, either restingor swimming, they are most commonly observedin waters within a few kilometers of shore(Riedman and Estes 1990), and higher densities arefrequently associated with shallow water (Laidre

    et al. 2002). Bodkin and Udevitz (1999) found 80%of the otters in PWS over water depths of < 40m although the proportion of the seafloor habitatwithin this bathymetric zone was only about 33%.Sea otters can also be found in high densitieswhere relatively shallow waters or islands occurfar offshore (Kenyon 1969). While they periodicallyhaul out on intertidal or supratidal (above thehigh tide line) shores (particularly during wintermonths) and generally remain close to the sea/landinterface, no aspect of their life history requiresleaving the ocean (Kenyon 1969, Riedman andEstes 1990).

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    Sea otters forage in diverse bottom types, fromfine mud and sand to rocky reefs. Recent researchemploying archival time-depth recorders recoveredfrom sea otters in southeast Alaska showed that84% of foraging occurred in depths of 2-30 m, andthat 16% of all foraging was between 30 and 100 m(Bodkin et al. 2004). Females dove to depths < 20m on 85% of their foraging dives while males doveto depths > 45 m on 50% of their foraging dives.Recent research from California suggests these

    patterns are similar among populations (Tinker etal. 2007), but additional research would improveconfidence in the generality of these results.

    Although it had been speculated that sea otters donot occupy protected inside waters such as occurin southeast Alaska and Puget Sound (Kenyon1969; Kvitek et al. 1991, Kvitek et al. 1993), recentcolonization of such habitat has been observed inPWS and southeast Alaska, including glacial fiordsand inside passages such as Icy Strait (Esslingerand Bodkin 2009). Although densities of sea ottersare clearly not uniform, within the geographicrange currently occupied there is little evidence

    that particular habitat types are unsuitable.However, there is also clear evidence that sometypes of habitat are preferred and capable ofsupporting high densities over extended periodsof time (Riedman and Estes 1990). In particular,where canopy-forming kelps occur (includingspecies ofMacrocystis, Eularia, and to a lesserextent Nereocystis), they provide preferred restinghabitat (Kenyon 1969, Riedman and Estes 1990).However, canopy-forming kelp is not a requiredhabitat element, and high densities of sea ottersoccur and persist in nearshore habitat wherekelp is absent, either seasonally or entirely, as aconsequence of unconsolidated substrates. This is

    particularly evident along coastal mainland Alaska(Kenyon 1969, Riedman and Estes 1990). Therealso appears to be a positive relationship betweenshoreline complexity and sea otter density (Kenyon1969, Riedman and Estes 1990). Again, althoughnot obligatory, headlands, coves, and bays appearto offer preferred resting habitat, particularlyto females with pups, presumably because theyprovide protection from high wind and seaconditions. Another recently recognized habitatattribute is refuge from predators. In a shallowlagoon that limited killer whale access at AdakIsland, Estes et al. (1998) found relatively stablesea otter numbers during a period when declines

    of up to 90% were detected outside the lagoon. Ashift in distribution toward very shallow (1-3 m),nearshore, highly protected areas in the AleutianIslands (USGS unpublished data) that has beendetected since the recent decline may represent aresponse to the risk of predation (see Section 3.A.).

    Comparatively few data are available to describerelations between sea otter densities and habitatcharacteristics, however it is generally recognizedthat rocky habitats support higher sea otterdensities compared to soft sediment habitats(Riedman and Estes 1990, Laidre et al. 2001,

    Laidre et al. 2002). Estimates of equilibriumdensities (those that are approximately stable andconsistent over time) across various populationswithin the sea otters range indicate values thatrange from about 1.5-17/km2 and generally considerhabitats out to the 40-55 m isobath (depth contour).Burn et al. (2003) and Estes (1977) provideestimates of equilibrium densities for the AleutianArchipelago and Amchitka Island of 16 and 17/km2 respectively. Equilibrium densities likely

    vary among habitats, with reported values specificto rocky habitats of about 1 to 8/km2 (Laidre et al.2001, Laidre et al. 2002, Lowry and Bodkin 2005,Gregr et al. 2008). Equilibrium densities from soft-sediment habitats are generally lower at < 1/ km2.In predominantly soft sediment habitats in PWSsea otter densities vary among areas, averagingabout 1.5/km2 and ranging from fewer than 1 toabout 6/km2 (Bodkin and Udevitz 1999, USGSunpublished data), although maximum densitiesin Orca Inlet, a shallow soft-sediment habitat, areup to 16/km2. Other estimates of maximum seaotter densities of about 12/km2 have been reportedfrom the Aleutian and Commander Islands

    (Kenyon 1969, Bodkin et al. 2000) where habitatsare predominantly rocky. In 2003, densitiesthroughout the Aleutian Archipelago are estimatedto be approximately 3% of equilibrium density(Estes et al. 2005).

    E. Population biology

    As in other sexually reproducing species, sea otterpopulations are ultimately regulated by age- andsex-specific rates of reproduction and survival.The life history patterns of sea otters are moresimilar to those of the pinnipeds and other marinemammals (with whom they share the ocean as a

    common environment) than to those of the otherlutrines (with whom they share a more recentcommon ancestor) (Estes and Bodkin 2002). Thesepatterns limit the potential for population increase.

    Male sea otters can attain sexual maturity by age 3but likely do not attain the social maturity requiredfor successful reproduction until >5 years old(Garshelis 1983). Variation in reproductive successamong males and the different reproductivestrategies they may employ are largelyunexplored. Female sea otters attain sexualmaturity as early as age 2, and by age 3 mostfemales are sexually mature (Bodkin et al. 1993,

    Jameson and Johnson 1993). Where food resourceslimit population growth, sexual maturation may bedelayed to 4-5 years of age. Reported reproductiverates of adult females range from 0.80 to 0.98births/yr (Siniff and Ralls 1991, Bodkin et al. 1993,Jameson and Johnson 1993, Riedman et al. 1994,Monson and DeGange 1995, Monson et al. 2000a,Tinker et al. 2006a). In areas where sea otterreproduction has been studied, reproductive ratesappear to be fairly consistent despite differencesin resource availability. Gestation, including aperiod of delayed implantation, requires about sixmonths. Although copulation and pupping can take

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    place at any time of year, there appears to be apositive relation between latitude and reproductivesynchrony. In California, pupping is weaklysynchronous to nearly uniform across months(Siniff and Ralls 1991, Riedman et al. 1994, Tinkeret al. 2006a), whereas in PWS a distinct peak inpupping occurs in late spring. In recently colonizedhabitats in Alaska where food is plentiful, puppingmay be less synchronous than in populations ator near equilibrium density (Bodkin and Monson

    2002).

    Females give birth to a single pup, althoughrare instances of twinning have been observed(Jameson and Bodkin 1986). The average durationof birth to weaning is about six months, resulting ina reproductive interval of approximately one yearfrom copulation to weaning. If a female loses herpup prior to weaning, she will soon enter estrusand breed again. Copulation occurs in the water,and a male may remain with an estrous female forseveral days (Riedman and Estes 1990), althougha female may breed with more than one male.Distinctive and sometimes severe wounds can

    result from the male biting the nose of the femaleduring copulation.

    Whereas reproductive output remains relativelyconstant over a broad range of ecologicalconditions, pup survival appears to be morestrongly influenced by resource availability. AtAmchitka Island, where the population was ator near equilibrium density prior to the recentdecline, dependent pup survival ranged from 22-40%, compared to nearly 85% at Kodiak Island,where food was not limiting and the populationwas increasing (Monson et al. 2000a). Femaleexperience apparently is important to the survival

    of offspring, with primiparous females (newmothers) generally less successful at weaning theirpups (Riedman et al. 1994, Monson and DeGange1995, Tinker et al. 2006a). Body condition (weight/unit length) of the mother at the time of birth alsoinfluences pup survival (Bodkin and Monson 2002).Female sea otters must spend large amounts oftime grooming and nursing their newborn pups,and keeping them warm and dry on their chestsor hauled out on rocks. This necessarily restrictsthe amount of time they can spend foraging. Afemale in poor condition will not be able to restricther feeding time to the extent a female in goodcondition can, and her pup will be exposed to

    longer periods in the water, and less groomingand nursing, while she feeds. The result is poorerpup survival during the first few weeks of life,the period during which most pre-weaning pupmortality occurs. This effect may be exaggeratedduring winter when conditions are particularlyharsh. In sea otter populations with limited foodresources, pups born in winter are more likelyto die soon after birth. This trend, combinedwith the tendency for females to enter estrussoon after losing a pup, tends to result in greatersynchronization of pup production.

    Sea otter populations generally consist of morefemales than males (Kenyon 1969, Bodkin etal. 2000). Age-specific survival of sea otters isgenerally lower among males (Kenyon 1969, 1982;Siniff and Ralls 1991, Monson and DeGange 1995,Bodkin et al. 2000), although variation in thepost-weaning survival of females appears to bethe primary mechanism of population regulationaround carrying capacity. Populations livingwith an abundance of food exhibit relatively high

    survival rates in all age classes compared to food-limited populations, with especially high relativesurvival in juvenile age-classes. Alternatively,populations at or above equilibrium density, withlimited food, show high variation in survival in theweeks following weaning. Post-weaning survivalis variable among populations and years, rangingfrom 18% to 86% (Monson et al. 2000a, Ballacheyet al. 2003). In general, once a sea otter survivesits first year of life, there appears to be a relativelygood probability that it will survive to senescence(old age), where density-dependent mechanismsstructure population abundance. Such may notbe case where density-independent factors such

    as predation are important. Survival of seaotters more than 2 years of age is generally high,approaching or exceeding 90%, but graduallydeclines over time (Bodkin and Jameson 1991,Monson et al. 2000a). In Alaskan and othernorthern populations, most mortality (other thanhuman-related) occurs during late winter andspring, presumably associated with harsh winterenvironmental conditions and seasonal declinesin prey availability (Kenyon 1969, Bodkin andJameson 1991, Bodkin et al. 2000, Watt et al. 2000).Maximum ages achieved by sea otters outsidecaptivity are about 22 years for females and 15years for males.

    The fetal sex ratio does not differ from 50:50(Kenyon 1982, Bodkin et al. 1993), yet sea otterpopulations may exhibit unequal sex ratios.Survival of juvenile (post-weaning) males inCalifornia exceeded that of juvenile females (Siniffand Ralls 1991) although the opposite was found atAmchitka Island (Kenyon 1969).

    Causes of mortality in sea otter populations aredifficult to determine. The probability of detectingand assigning cause of death depends on the cause.For example, the carcass of a sea otter that dies ofstarvation is more likely to be recovered than that

    of one killed by a predator. Documented sourcesof mortality include predation, starvation, disease,oil spills, incidental take in fisheries, harvest, andintra-specific aggression. In California, infectiousdisease was implicated as the cause of death fornearly 40% of 195 carcasses analyzed between1992 and 1995 (Thomas and Cole 1996) and 63%of 105 carcasses analyzed between 1998 and 2001(Kreuder et al. 2003). However, these estimatesmay not accurately reflect the causes of death inthe population as recovered carcasses are likelynot an unbiased sample (as mentioned above) andthe cause is unknown for the majority of deaths: an

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    estimated 40-60% of carcasses are not recoveredand the cause of death cannot be determined forabout 72% of those that are recovered (Esteset al. 2003, Gerber et al. 2004). Disease factorscontributing to mortality included peritonitiscaused by acanthocephalan parasites, protozoanencephalitis, coccidioidomycosis, and bacterialinfections. As noted previously, sea ice can be amortality factor as well. Recognized sea otterpredators include the white shark (Carcharodon

    carcharias), brown bear (Ursus arctos), wolf,red fox, wolverine, killer whale, and bald eagle(Haliaeetus leucocephalus) (Kenyon 1969, Amesand Morejohn 1980, Riedman and Estes 1990,Monson and DeGange 1995, Hatfield et al. 1998,Bodkin et al. 2000). Bald eagles prey primarilyon young pups. Gelatt (1996) found that motherswith young pups fed less often overall, and whenthey did feed it was often nocturnally, apparentlyto avoid exposing their pup to eagle predation.Declining sea otter populations across the Aleutianarchipelago during the 1990s have been attributedto increased predation by killer whales (Estes et al.1998).

    Prior to the sea otter decline in the AleutianIslands late in the 20th century, populationdensities were generally thought to be limitedby prey availability, with mortality being densitydependent and increasing during periods of foodshortage and severe weather. This pattern ofelevated winter mortality, particularly amongjuveniles and old individuals, was initially observedat Amchitka Island in the 1950s and 1960s (Kenyon1969). In the Commander Islands, the sea otterpopulation declined by 41% in a single year,following 10 years of increasing density, decliningprey populations, and declining weights of adult

    male otters (Bodkin et al. 2000). It is possible thatsome of the disease-related mortality in Californiais ultimately linked to prey availability, and thecessation of population growth in the regions ofhighest sea otter density in California is associatedwith declining body condition and increasedpercentage of time spent foraging, both suggestiveof food limitation (Bentall et al. 2005, Tinker et al.2006a, Tinker et al. 2006b).

    Relatively few studies have investigated therelations between the physical and biologicalattributes that contribute to variation inproductivity of nearshore marine invertebrates,

    such as the clams, mussels, and crabs that seaotters consume, and how that variability inproductivity affects variation in annual sea ottersurvival (Lowry and Bodkin 2005). Given theobserved variation in sea otter survival and therecognized role of food in regulating sea otterpopulations, understanding those relations wouldfacilitate empirical measures of the relativecontributions of predation and primary produc-tion as controlling factors in structuring nearshoremarine communities. Due to the relatively smallsize of their home ranges, sea otters integratephysical and biological attributes of the ecosystem

    over small spatial scales. Further, because theyoccur near shore, sea otters, their prey, andphysical and biological ecosystem attributes can beaccurately and efficiently monitored, providing astrong foundation for understanding mechanismsand interactions among factors that regulate seaotter populations.

    Our understanding of the frequency, magnitude,causes, and consequences of changes in sea otter

    populations is constrained by the brief temporalperspectives imposed by the short window ofhuman observation and written history. Oneconsequence of this narrow time perspective is thatwe may view causes and consequences of changeas novel, even when they are not. Relativelyunexplored evidence from archeological remainssuggests that local abundance of sea ottersand other nearshore marine species has variedsignificantly over millennial time scales (Simenstadet al. 1978). An improved understanding oflong-term population changes would provideadded context for evaluating and responding tocontemporary fluctuations in sea otter populations.

    F. Behavior

    ReproductionMale sea otters gain access to estrous females byestablishing and maintaining territories from whichother males are excluded (Kenyon 1969, Garsheliset al. 1984, Jameson 1989). Territories may belocated in or adjacent to female resting or feedingareas, or along travel corridors between thoseareas. Territories are occupied continuously orintermittently over time (Loughlin 1980, Garsheliset al. 1984, Jameson 1989). Male occupancy in aterritory may extend over 6 to 9 years (Riedman

    and Estes 1990). Male territoriality results inpartial segregation of the sexes, and males thatdo not occupy territories tend to reside in densebachelor aggregations (Kenyon 1969, Bodkinet al. 2000). Males that do not defend territories(transients) may gain access to receptivefemales by traveling through or adjacent to maleterritories and female areas. Male aggregationareas identified by Kenyon in 1962 at AmchitkaIsland persisted through at least 1995 (USGSunpublished data). In California, many malesthat defend territories for part of the year mayperiodically move to bachelor aggregation areas,apparently to take advantage of seasonally and

    locally abundant food resources (Jameson 1989,Tinker et al. 2006b, Kage 2004). Female choice inmate selection is facilitated by females travelingamong male territories, although males may try tosequester estrous females within their territory.Adult male sea otters in California maintainterritories that average about 0.4 km2 (Jameson1989). Adult females apparently move freelyamong these territories, but the territory holderaggressively excludes juvenile males. Although therole of male territoriality in regulating populationdensity is largely unexplored, territories likelyserve to increase individual reproductive success.

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    Adult males frequently harass females with largepups in an apparent effort to force separation,thus inducing the female to enter estrus so thathe can inseminate her and she will bear hisoffspring. Copulation occurs repeatedly during abrief consortship, after which the male and femaleseparate.

    The sea otters polygynous mating system (onemale can mate with more than one female) likely

    evolved in response to the high densities theyachieved in prehistoric populations not affectedby humans, which promoted male competition forfemales. Polygynous mating systems are typicalof all otariids (eared seals) and some phocids(true seals) in temperate-latitude systems butapparently are rare or absent in other species ofotters. As is true for many polygynous species,male sea otters provide no parental care (Estes1989).

    DivingDiving occurs during grooming, traveling andforaging. Grooming dives usually occur before

    feeding or resting periods, and are of shortduration and shallow depth. Because locomotionis more efficient under water than on the surface(Williams 1989), otters frequently make relativelylong (30-60 s), shallow dives while travelingbetween resting and feeding areas. Foraging divesare predominantly to the sea floor, although canopyforaging in kelp forests for snails and crabs iscommon in California. Foraging dives are typicallylonger in duration with greater rates of descentand ascent than dives of other function. Attributesof dives (duration, depth, ratio of bottom time todive time, and rates of descent and ascent) aresignificantly different for traveling, grooming, and

    foraging dives (Bodkin et al. 2004), and can be usedto classify dives according to their function.

    Three general types of diving data have beenobtained through direct visual observation (Esteset al. 1981, Riedman and Estes 1990, Calkins 1978,Garshelis 1983, Doroff and Bodkin 1994, Doroffand DeGange 1994), radio-telemetry with remoteinformation acquisition (Ralls et al. 1996), and mostrecently archival time-depth recorders (TDRs)(Bodkin et al. 2004, Tinker et al. 2006b). Diveattributes from visual observations include diveduration, surface intervals between dives, andapproximate water depths at the estimated dive

    locations. These data are inherently biased againstanimals foraging well away from shore (Ralls et al.1996). Thus, estimates of average and maximumdive duration from animals instrumented withradio-transmitters are substantially longer thanthose obtained visually (Ralls et al. 1996, Bodkin etal. 2004).

    Mean swimming speeds during descent andascent in foraging dives average about 1 m/s. InCalifornia, average dive times are longest forjuvenile males and shortest for adult femaleswith dependent pups (Ralls et al. 1996). These

    differences are likely because juvenile malesforage in deeper water offshore while femaleswith pups forage in shallower water near shore.Maximum reported dive durations are 246 s inCalifornia (Ralls et al. 1996) and 386 s in Alaska(USGS unpublished data). Dive times and surfaceintervals correlate with water depth, althoughthe deepest dives are not necessarily associatedwith maximum dive times. Surface intervals arehighly correlated with prey size and type, with the

    longest intervals associated with the largest prey,thus reflecting handling and consumption times(Ralls et al. 1996, Tinker et al. 2007). Sea otterscommonly dive to depths exceeding 40 m in theAleutian Islands and there is one record of a seaotter drowned in a crab pot set in 91 m of water(Newby 1975).

    In California, it was recently demonstrated thatTDR data alone are sufficient to detect dietarydifferences between individuals (Tinker et al. 2007),and information recently obtained from southeastAlaska using TDRs confirms the foragingspecializations documented in California (Estes

    et al. 2003a, Tinker et al. 2007). Archival TDRsidentified individual- and sex-related differencesin mean and maximum foraging dive attributesand depth distributions (Bodkin et al. 2004). Abimodal pattern in forage depth distribution wasdetected for most of the individuals sampled, withpeaks in foraging between 5-15 m and 30-60 m.Generally, adult females dove to shallower depthsthan adult males, although some females regularlydove to depths exceeding 60 m. Most adult malesforaged at depths between 40 and 60 m, althoughseveral repeatedly dove to depths exceeding 60m. Maximum dive depths were 76 m for femalesand 100 m for males (Bodkin et al. 2004). Similar

    patterns appear to occur in California (Tinker et al.2006b, USGS unpublished data), but more researchis needed to document the generality of thesefindings in other populations.

    Activity budgetsTime budgets describe the allocation of time tospecific categories of behavior, such as resting,grooming, foraging, or social interaction. Thefundamental premise is that food resourcesfrequently limit population abundance, and that theproportion of time individuals allocate to foragingreflects food availability (Gelatt et al. 2002). Seaotter activity budgets have been estimated at 7

    different locations and during 13 different timeperiods, including populations that were increasing,stable, and decreasing (Gelatt et al. 2002). Despitethis breadth of research, conclusions aboutthe utility of time budgets to assess sea otterpopulation status have been inconsistent (Shimekand Monk 1977, Loughlin 1979, Estes et al. 1982,Estes et al. 1986, Garshelis et al. 1986, Rallsand Siniff 1990, Gelatt et al. 2002). Some of thedivergence in results and conclusions stems fromdifferences in accuracy and precision produced byvarious methods (visual vs. telemetry), samplingdesigns (day vs. day and night, and sample

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    sizes), uncertainty in population status relativeto carrying capacity at the time of study, and thesometimes overwhelming influence of samplingvariance (including within-individual variationacross time, as well as variation among individuals,sexes, and age cohorts).

    In general, adult male sea otters spend less timeforaging (37%) than younger males (44%) orfemales, adult females spend less time foraging

    (36-47%) than younger females (50%), and femaleswith young pups spend less time feeding (21%)than females with older pups (52%) (Gelatt et al.2002). Recent calculations of time budgets basedon TDR data from southeast Alaska (Bodkin et al.2007a) and comparisons between telemetry- andTDR-based activity budgets in California (Tinkeret al. 2006b, Bentall 2005, USGS unpublisheddata) support the premise that the amount of timeallocated to foraging reflects prey availability,and thus TDR-derived activity budgets may beof use in evaluating population status relative toequilibrium density.

    Movements and home rangesSea otters exhibit complex movement patternsrelated to habitat characteristics, socialorganization, and reproductive biology. It is likelythat movements differ depending on whethera population is at or near carrying capacity orhas access to unoccupied suitable habitat intowhich it can expand (Riedman and Estes 1990).Most research on sea otter movements has beenconducted where unoccupied habitat is availableto dispersing animals. For example, dominantadult males in California generally occupy anddefend relatively small territories, which varyseasonally between summer-fall (4.0 km2; 1.1 km

    of coastline) and winter-spring (7.8 km2; 2.2 kmof coastline), frequently moving relatively longdistances to reach male aggregations (average= 80.1 km; maximum = 418 km) (Jameson 1989,Ralls et al. 1996, Kage 2004, USGS unpublisheddata). Juvenile females may also occasionallymake very long movements (maximum = 235 km;USGS unpublished data). Adult females rarelymove farther than 20 km, although they generallyoccupy home ranges larger than the territories ofterritorial males (Ralls et al. 1988). Early researchin the Aleutian Islands by Lensink (1962) andKenyon (1969) found that males had larger homeranges than females, and those authors described

    the female sea otters home range as including8-16 km of contiguous coastline. Adult malehome ranges in PWS are 4.6-11.0 km2 and adultfemale home ranges are 1.0-4.8 km2 (Garshelisand Garshelis 1984). In PWS, a telemetry studydocumented movements by adult males of up to 100km between male aggregation areas and breedingareas (Garshelis and Garshelis 1984a). Recentestimates of annual home range sizes in westernPWS were significantly smaller for territorialmales1 (50% kernel home range = 5.4 km2, and1 The % kernel home range is the area where an

    animal can be found that % of the time.

    90% kernel home range = 9.6 km2) than for adultfemales (50% kernel home range = 6.8 km2, and90% kernel home range = 23.8 km2) (Ballacheyand Bodkin 2006). Additional telemetry studieson juveniles in PWS, and adult males and femalesalong the Alaska Peninsula and in the Kodiakarchipelago (USGS unpublished data, Monnet et al.1988), documented movements typically of 50 kmor less. Comparable data are not available fromother areas in Alaska.

    Although annual and lifetime home ranges suggestlimited movements throughout much of theirrange, sea otters can move much greater distanceswhen translocated. In California, translocatedanimals returned as much as 318 km from releasesites back to capture sites (Ralls et al. 1992). InAlaska, a female treated and then released afterthe T/V Exxon Valdez oil spill traveled 400 kmfrom her release site (Monnet et al. 1990).

    While sea otters are somewhat constrained bythe 100 m depth profile, they can navigate somedistance over deep water. Translocated sea otters

    have traveled distances of up to 50 km, over waterdeeper than their maximum foraging depth, fromSan Nicolas Island to the mainland along southernCalifornia (Rathbun et al. 1990). Similar travel,but unrelated to translocation, was documented byBodkin et al. (2000) from Medny to Bering Island inthe Commander Islands.

    Conventional very high frequency (VHF)telemetry has most commonly been used toestimate sea otter home ranges and movements.Because relocation probabilities diminish asdistance from last location increases, movementestimates from such studies may be negatively

    biased. Additional research employingtechnologies that reduce recognized sources ofbias (e.g., global positioning system, GPS) shouldprovide better estimates. Also, in the event oflocalized extinctions within geographically isolatedsegments of habitat (e.g., island groups in theAleutian Islands), recolonization may become moreproblematic as the required dispersal distanceincreases.

    G. Foraging ecology

    Sea otters are generalist predators, known toconsume more than 150 different prey species

    (Kenyon 1969, Riedman and Estes 1990, Estesand Bodkin 2002). With few exceptions, theirprey consists of sessile or slow-moving benthicinvertebrates such as mollusks, crustaceans, andechinoderms. Foraging occurs in habitats withrocky and soft-sediment substrates from the highintertidal to depths slightly in excess of 100 m.Preferred foraging habitat is generally in depths ofless than 40 m (Riedman and Estes 1990), althoughstudies in southeast Alaska have found that someanimals forage mostly at depths of 40-80 m (Bodkinet al. 2004).

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    The diet of sea otters is usually studied byobserving prey items brought to the surface forconsumption, and therefore diet composition isusually expressed as a percentage of all identifiedprey that belong to a particular prey species ortype. Although the sea otter is known to preyon a large number of species, only a few tend topredominate in the diets of individual otters inany particular area. Prey type and size dependon location, habitat type, season, and length of

    occupation. In California, otters foraging overrocky substrates and in kelp forests mainlyconsume decapod crustaceans, gastropod andbivalve mollusks, echinoderms, and worms (Ebert1968, Estes et al. 1981, Tinker et al. 2008). Inprotected bays with soft sediments, otters mainlyconsume infaunal clams (Saxidomus nuttalliiand Tresus nuttallii) (Kvitek et al. 1988). Alongexposed coasts with soft sediments, the Pismo clam(Tivela stultorum) is a common prey (Stephenson1977). Important prey in Washington Stateinclude crabs (Cancerspp., Pugettia spp.), octopus(Octopus spp.), intertidal clams (Protothaca spp.),sea cucumbers (Cucumaria miniata), and red

    sea urchins (Strongylocentrotus franciscanus)(Kvitek et al. 1989). The predominantly soft-sediment habitats of southeast Alaska, PWS, andKodiak Island support populations of clams thatare the primary prey of sea otters. Throughoutmost of southeast Alaska, burrowing clams(species ofSaxidomus, Protothaca, Macoma,and Mya) predominate in the sea otters diet(Kvitek et al. 1993). They account for more than50% of the identifie