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Polar Bioi (2011) 34: 1065-1084 DOl 1O.1007/s00300-011-0967-4 Projected status of the Pacific walrus (Odobenus rosmarus divergens) in the twenty-first century Chadwick V. Jay' Bruce G. Marcot • David C. Douglas Received: 2 September 20101 Revised: 24 January 20111 Accepted: 2 February 20111 Published online: 2 March 2011 © US Government 2011 Abstract Extensive andrapid losses of sea ice in the Arctic the end of the century. The summed probabilities of vulner have raised conservation concerns for the Pacific walrus able, rare, and extirpated (p(v,r,e)) increased from a current (Odobenus rosmarus divergens), a large pinniped inhabit level of 10% in 2004 to 22% by 2050 and 40% by 2095. ing arctic and subarctic continental shelf waters of the The degree of uncertainty in walrus outcomes increased Chukchi and Bering seas. We developed a Bayesian monotonically over future periods. In the model, sea ice network model to integrate potential effects of changing habitat (partiCularly for summer/fall) and harvest levels had environmental conditions and anthropogenic stressors on the greatest influenceon future population outcomes. Other the future status of the Pacific walrus population at four potential stressors had much smaller influences on walrus periods through the twenty-first century. The model frame outcomes, mostly because of uncertainty in their future work allowed for inclusion of various sources and levels of states and our current poor understanding of their mecha knowledge, and representation of structural and parameter nistic influenceon walrus abundance. uncertainties. Walrus outcome probabilities through the century reflected a clear trend of worsening conditions for Keywords Status· Walrus· Odobenus· the subspecies. From the current observation period to the Bayesian network· Sea ice end of century, the greatest change in walrus outcome prob abilities was a progressive decrease in the outcome state of robust and a concomitant increase in the outcome state of Introduction vulnerable. The probabilities of rare and extirpated states each progressively increased but remained <10% through Climate warming and reductions in sea ice habitats present a particularly difficultchallenge to the conservation of pola,r marine mammals. Arctic-wide generalizations on species Electronic supplementary material The online version of this specific effects of climate change are difficult to make article (doi: 1 0.1 007/s00300-0 11-0967 -4) contains supplementary because the sensitivity and response of marinemammals to material, which is available to authorized users. environmental changes in the Arctic are complex and can vary among and within species (Laidre et al. 2008). The C. V. Jay (�) US Geological Survey, Alaska Science Center, Pacific walrus (Odobenus rosmarus divergens) is a large 4210 University Drive, Anchorage, AK 99508, USA pinniped inhabiting arctic and subarctic continental shelf e-mail: [email protected] waters of the Chukchi and Bering seas. Concerns over the future of the Pacific walrus, especially under the stress of B. G. Marcot US Department of Agriculture, Forest Service, climate change, prompted the US Fish and Wildlife Service Pacific Northwest Research Station, Portland Forestry Sciences to initiate a status review in September, 2009, to determine Laboratory, 620 SW Main, Suite 400, Portland, OR 97205, USA whether listing the subspecies as threatened or endangered is warranted under the Endangered Species Act (US Fish D. C. Douglas US Geological Survey, Alaska Science Center, and Wildlife Service 2009). To aid this endeavor, and to 3100 National Park Road, Juneau, AK 99801, USA focus new research and monitoring efforts, we synthesized � Springer 1066 Polar BioI (2011) 34:1065-1084 Fig. 1 Study area used for pro jecting Pacific walrus status in the twenty-first century studies and understanding of the Pacific walrus into a In spring, most adult female and young walrusesfollow knowledge-based model to evaluate possible future influ the receding ice pack northward to summer in the Chukchi ences of anthropogenic stressors and changing environmen Sea, while many of the adult males move toward coastal tal conditions on the Pacificwalrus population. areas to summer in nearshore areas of the Bering Sea and The Pacificwalrus is currently distributed in Russian and northern coast of Chukotka. In autumn, female and young Alaskan waters, and ranges in the north from the eastern walruses migrate with the developing sea ice southward East Siberian Sea to the western Beaufort Sea, and in the into the Bering Sea, where they are joined by the males in south from eastern Kamchatka to Bristol Bay (Fay 1982) late autumn and winter (Fay 1982). 1). (Fig. In winter, the entire Pacific walrus population Walruses are very gregarious and occur in groups of up resides in the Bering Sea. Breeding occurs in January and to "-'500walruses (Fay 1985; Speckman et al. 2(10). Group February. Leks are formed where breeding males display sizes of hauled out walruses tend to be larger when they are and vocalize from water alongside groups of females on shore than on ice (Fay 1985). Seasonal dynamics of sea hauled out on ice, and copulation occurs in water (Fay et al. ice cover in the Chukchi and Bering seas allow walruses to 1984). Most calving occurs in April-June (15-16 month exploit a wide area of the continental shelf during the year. pregnancy), and mothers care for and nurse their newborn Adult male walruses have dorsal inflatable pharyngeal calves on the ice (Fay 1985). Little is known of ice prefer pouches, which allow them to sleep at the surface in open ences for breeding and calving activities; however, wal water for extended periods (Fay 1960) between foraging ruses require ice floes large enough to support their weight trips from land in summer (e.g. Jay et al. 2(01). (Fay 1982; Simpkins et al. 2003). Within its range, Pacific Reduced summer sea ice over the continental shelf in the walruses typically occur in areas of unconsolidated ice, Chukchi Sea in the past decade has resulted in increased open leads, and thin ice where they can create breathing use of land haul-outs by adult females and young during holes, and they avoid areas with very high concentrations ice-free periods (Jay and Fischbach 2008; Kavry et al. of thick ice, such as in the Chukchi Sea in winter (Bums 2(08). This was particularly evident in the summer and et al. 1980, 1981; Fay 1982). fall of 2007 and 2009. During these years, thousands of � Springer Polar BioI (2011) 34:1065-1084 1067 walruses hauled out along the coast of northwesternAlaska, surveys to contain walruses were unable to be surveyed and tens of thousands of walruses hauled out along the (Speckman et al. 201 coast of northern Chukotka when ice disappeared from the Pacificwalruses forage on the seafloorof the continental shelf. These events led to the trampling and death of hun shelves (Fay and Bums 1 Jay et aL where ben- dreds of walruses in Alaska and thousands in Russia (calves thic production is high (Grebmeier et aL Bluhm and are p<h'1:icularly vulnerable), presumably when herds were Gradinger lli,d benthic diving is energetically feasi disturbed from anthropogenic and predator stimuli (Kavry ble (e.g. Costa and Gales Walruses feed on a wide et al. 2008; Kochnev et al. 2008; Fischbach et al. variety of organisms including small cmstaceans, worms, A. Koc!h,ev, ChukotTTh"'RO,pers. comm. 2009). An unusu snails, clams, marine birds, and seals (Fay 1982; Sheffield ally high number of walruses hauled out and high levels of and Grebmeier but their diet most frequently con mortality occurred on the shores of Wrangel IsI<hTld, Russia sists of clams, snails, and polychaete worms (Sheffieldand (Ovsyanikov et al. Increased use of land haul-outs Grebmeier by adult females and young in summer could also result in Some of the highest levels of soft-bottom benthic faunal increased energy expenditures from foraging trips originat biomass in the world occur in the nonhern Bering and ing from shore and reduced access to preferred feeding Chukchi seas (Grebmeier et al. Bluhm and Gradinger grounds. 2008 ). In seasonally ice-covered waters, such as the The Pacific walrusis harvested for subsistence by Alaskan Chukchi and Bering seas, the onset of sea ice melt and the and Russian Native communities. Estimates of walrus duration of open water have a direct influence on the rela harvest levels from1960 through 2007 range from 3,184 to tive amounts of organic carbon retained in the water 16,127 walruses per year (US Fish and Wildlife Service column and exported to the sediments (Grebmeier et al. which includes adult and juvenile walruses (Fay and High primary production, with simultaneously low Bowlby 1 Estimates of current harvest levels are zooplankton grazing, resultsin much of the organic matter 4,960-5,457 wal."Usesper year (2003-2007 harvest records). sinking to the seafloor and enhancing benthic production Factors affecting recent harvest levels include cessation of (Grebmeier and Bfu'TY199 1). Reductions in sea ice have the Russian commercial harvests after 1991, changes in politi potential to reduce benthic production and increase pelagic cal, economic, and social conditions of subsistence hunting consumption in Arctic marine ecosystems; however, communities in Alaska and Russia, and the effects of vari detailed biological consequences of reduced sea ice are able weather and ice conditions on hunting success. Current difficult to predict middepend on regional conditions gov walrus mortality rates from fisheries interactions and other erning productivity (Piepenburg Grebmeier et al. known human activities (incidental takes) are estimated at b; Lalande et al. 2007; Bluhm and Gradinger about 3 walruses per year (US Fish and Wildlife Service Such shifts could result in reduced abundance of benthic 2Ul Thus, the greatest humall-caused direct mortality of prey for walruses. walruses is from subsistence harvest.

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