Influence of climate change on summer-fall distribution of pacific walrus in the western Bering Sea: analysis of reasons and consequences

Recently the sea ice edge at Chukotka retreats further northward in summer and new ice formation begins in a month later in autumn than in previous decades because of climate change that changes the pacific walrus Odobenus rosmarus divergens habitat. Now the Bering Sea becomes completely clear of the ice by start of the spring migration of walruses. In these conditions, the walrus migration routes and feeding grounds location changes. Permanent walrus rookeries on the eastern coast of Chukotka and Kamchatka disappeared (Verkhoturov Island, Karaginsky Island, Bogoslov Islands, Anastasia Bay, Cape Dezhnev, Cape Sery, Cape Olutorsky, Cape Zosima) and new rookeries have formed in the Bering Sea (at Meinypylgino and Enmelen) and on the Arctic shore of Chukotka (at Vankaren and Cape Shmidt). Benthos community has changed, too. As the result, quality of the walrus habitat became worse, the sickness and mortality of young animals increased and the reproduction rate decreased. Formerly stable large walrus rookery in the Krest Bay (Meeskyn) was surveyed in 2016. Together with Retkyn rookery in the Rudder Bay it formed the large Anadyr group of walruses, about 50,000 of the animals gathered on these rookeries in the 1980s. However, the group began to fluctuate with decreasing trend since the 1990s: its number was estimated as 5,000-6,000 animals in 1996, 12,000 in 1997, 30,000 in 1999, 26,000 in 2000, 6,000-8,000 in 2001-2007, 2,000 in 2008. Meeskyn rookery did not function since 2006, though small group of 200 animals was observed here in 2016. Two hypotheses on this tendency are proposed: i) negative influence of climate change on reproduction of walruses in the Chukchi Sea; ii) depletion of the walrus feeding grounds in the Anadyr Bay caused by climate change and excessive abundance of the population.