Bering Sea | Mammals
Determining cryptic life history milestones using isotopic markers in northern fur seal ( Callorhinus ursinus ) vibrissae Presenter: Tonya Zeppelin , Tonya.Zeppelin@noaa.gov, National Marine Fisheries Service, Marine Mammal Laboratory Brian Brost , Brian.Brost@noaa.gov, Marine Mammal Laboratory Devin Johnson , Devin.Johnson@noaa.gov, Pacific Islands Fisheries Science Center
Carolyn Kurle , ckurle@ucsd.edu, University of California, San Diego Brandon Güell , bguell@bu.edu, University of California, San Diego Christina Kelleher , christinakelleher16@gmail.com, University of California, San Diego Michael Williams , michael.williams@noaa.gov, NOAA/NMFS Anne York , york@zipcon.net, YoDA
Northern fur seals ( Callorhinus ursinus ; NFS) have declined significantly on the Pribilof Islands, Alaska, their primary breeding site. The reasons for the decline are currently unknown, however, low juvenile survival is thought to be a possible cause. NFS are born in July, nurse intermittently and depart the breeding sites around four months to undertake extensive far-ranging pelagic migrations and typically do not return to the breeding grounds until two years of age. Despite extensive research and recent advances in our understanding of NFS ecology, it’s currently not possible to reconstruct the timing of life history events for individual animals. During 2014 and 2015, vibrissae were collected from 13 pup and 8 juvenile (2-4yo) male NFS taken with collaboration from subsistence users on the Pribilof Islands. Whiskers were serial sampled and analyzed for stable isotope values of carbon (δ13C) and nitrogen (δ15N) to better understand the timeline and character of life history events that occur during the early years of NFS lives. We developed models that identified isotopic markers for birth, weaning, and migratory cycles. Our results indicate that NFS are born around 11 July (SD = 31d) and do not forage independently prior to weaning when they depart the breeding islands on their first winter migration. Although there was variability among individuals, whiskers from 3- and 4-year-old juveniles exhibited oscillations in their δ13C values that corresponded to annual migrations. Our data indicate differences in whisker growth rates through time and among individuals. Collection and analysis of additional samples will help us more accurately estimate the timing of specific life history events identified by isotopic markers so that these estimates can ultimately be linked with biological and environmental data and compared across breeding sites.
Alaska Marine Science Symposium 2023 263
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