The sun, moon, wind, and biological imperative - shaping contrasting wintertime migration and foraging strategies of adult male and female Northern Fur Seals (Callorhinus ursinus)

• Published in: PLoS ONE
• Main Authors: Sterling, JT, Springer, AM, Iverson, SJ, Johnson, SP, Pelland, NA, Johnson, DS, Lea, M-A, Bond, NA
• Format: Article in Journal/Newspaper
• Language: English
• Published: Public Library of Science 2014
• Subjects: Environmental Sciences; Environmental Science and Management; Wildlife and Habitat Management; Bering Sea; Pacific; Alaska; Callorhinus ursinus
• Online Access: https://doi.org/10.1371/journal.pone.0093068; http://www.ncbi.nlm.nih.gov/pubmed/24722344; http://ecite.utas.edu.au/91535

Adult male and female northern fur seals (Callorhinus ursinus) are sexually segregated in different regions of the NorthPacific Ocean and Bering Sea during their winter migration. Explanations for this involve interplay between physiology,predator-prey dynamics, and ecosystem characteristics, however possible mechanisms lack empirical support. Toinvestigate factors influencing the winter ecology of both sexes, we deployed five satellite-linked conductivity, temperature,and depth data loggers on adult males, and six satellite-linked depth data loggers and four satellite transmitters on adultfemales from St. Paul Island (Bering Sea, Alaska, USA) in October 2009. Males and females migrated to different regions ofthe North Pacific Ocean: males wintered in the Bering Sea and northern North Pacific Ocean, while females migrated to theGulf of Alaska and California Current. Horizontal and vertical movement behaviors of both sexes were influenced by windspeed, season, light (sun and moon), and the ecosystem they occupied, although the expression of the behaviors differedbetween sexes. Male dive depths were aligned with the depth of the mixed layer during daylight periods and we suspectthis was the case for females upon their arrival to the California Current. We suggest that females, because of their smallersize and physiological limitations, must avoid severe winters typical of the northern North Pacific Ocean and Bering Sea andmigrate long distances to areas of more benign environmental conditions and where prey is shallower and more accessible.In contrast, males can better tolerate often extreme winter ocean conditions and exploit prey at depth because of theirgreater size and physiological capabilities. We believe these contrasting winter behaviors 1) are a consequence ofevolutionary selection for large size in males, important to the acquisition and defense of territories against rivals during thebreeding season, and 2) ease environmental/physiological constraints imposed on smaller females