Summer social structure of crabeater seal Lobodon carcinophaga in the Amundsen Sea, Antarctica

Abstract

During the PS75 expedition of ice-breaking RV Polarstern in the Amundsen Sea, in February–March 2010, we studied the at-sea quantitative distribution of the “upper trophic levels,” seabirds and marine mammals. In the Amundsen Sea Embayment, 14,200 pinnipeds belonging to four species were recorded (2100 during 670 half-hour transect counts from the bridge and 12,100 during 50 h of helicopter flight). Crabeater seal Lobodon carcinophaga represented more than 97 % of the total. Two types of major aggregations of crabeaters were noted: on the one hand, very large groups hauled out on the pack ice, composed mainly of adults/bachelors and very few calves. On the other hand, swimming pods of calves were accompanied by one or two leading adults around icebergs. Our interpretation is that, after the beginning of the reproduction period with trios (cow, calf and future father) scattered on pack ice, such pods can be considered the last step of the breeding cycle.