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Ontogenetic dietary information of the California sea lion (Zalophus californianus) assessed using stable isotope analysis

Authors

  • Anthony J. Orr,

    1. The National Marine Mammal Laboratory, Alaska Fisheries Science Center, NOAA, 7600 Sand Point Way NE, Seattle, Washington 98155, U.S.A. and Washington Cooperative Fish and Wildlife Research Unit, School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington 98195, U.S.A. E-mail: tony.orr@noaa.gov
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  • Seth D. Newsome,

    1. Department of Zoology and Physiology, University of Wyoming, 1000 East University Avenue, Department 3166, Laramie, Wyoming 82071, U.S.A.
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  • Jeffrey L. Laake,

    1. The National Marine Mammal Laboratory, Alaska Fisheries Science Center, NOAA, 7600 Sand Point Way NE, Seattle, Washington 98155, U.S.A.
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  • Glenn R. VanBlaricom,

    1. Washington Cooperative Fish and Wildlife Research Unit, School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington 98195, U.S.A.
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  • Robert L. DeLong

    1. The National Marine Mammal Laboratory, Alaska Fisheries Science Center, NOAA, 7600 Sand Point Way NE, Seattle, Washington 98155, U.S.A.
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Abstract

We used stable carbon (δ13C) and nitrogen (δ15N) isotopes to examine ontogenetic dietary changes in 289 California sea lions (Zalophus californianus) at San Miguel Island, California during 2004–2007. Tissues analyzed included fur, red blood cells, plasma, and serum. For all tissues, pups had higher δ15N values and lower δ13C values compared to adults, which indicated that pups were feeding higher trophically than older conspecifics and on a lipid-rich milk diet prior to weaning. Yearling δ15N values were slightly lower than pup or nearly indistinguishable from adult values depending on the tissue analyzed, indicating a dietary shift from maternal dependency to independent foraging. Juveniles (2–4 yr) and adults (>4 yr) had similar δ15N values indicating they fed at a similar trophic level. There did not appear to be a pronounced dietary shift in δ13C values. However, δ13C values integrated with telemetry data indicated that postweaned individuals fed in similar foraging areas. Dietary changes during early life stages may be due to differences in physiology, morphology, experience, or energetic requirements; however, young animals are able to attain the skills needed to consume adult prey types near the end of their second year of life.

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