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Modeling the diet of humpback whales: An approach using stable carbon and nitrogen isotopes in a Bayesian mixing model

Authors

  • Briana H. Witteveen,

    1. Department of Biology,
      University of Central Florida,
      4000 Central Florida Boulevard,
      Orland, Florida 32816, U.S.A.
      and
      School of Fisheries and Ocean Sciences,
      University of Alaska Fairbanks,
      118 Trident Way,
      Kodiak, Alaska 99615, U.S.A.
      E-mail: bree.witteveen@alaska.edu
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  • Graham A. J. Worthy,

    1. Department of Biology,
      University of Central Florida,
      4000 Central Florida Boulevard,
      Orland, Florida 32816, U.S.A.
      and
      Hubbs-SeaWorld Research Institute,
      6295 Sea Harbor Drive,
      Orlando, Florida 32821, U.S.A.
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  • Robert J. Foy,

    1. Kodiak Laboratory,
      Resource Assessment and Conservation Engineering Division,
      Alaska Fisheries Science Center,
      National Marine Fisheries Service,
      National Oceanic and Atmospheric Administration,
      301 Research Court,
      Kodiak, Alaska 99615, U.S.A.
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  • Kate M. Wynne

    1. School of Fisheries and Ocean Sciences,
      University of Alaska Fairbanks,
      118 Trident Way,
      Kodiak, Alaska 99615, U.S.A.
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Abstract

Humpback whales are considered generalist predators, feeding on schooling fish, and zooplankton, but variability likely exists among regional feeding aggregations. We explored the diet of one feeding aggregation of humpback whales near Kodiak Island, Alaska, through analysis of the stable carbon (δ13C) and nitrogen (δ15N) isotope ratios of their skin and regional prey sources. Humpback whales were sampled during the summer feeding season over 3 yr (n= 93; 2004–2006). Prey samples were collected from the same region during trawl surveys conducted between 2003 and 2005. Isotope values of humpback whale skin and prey were entered into a Bayesian dietary mixing model to estimate feasible contributions of prey to humpback diets. Diet results indicated that humpbacks feed heavily on euphausiids, but also consume juvenile walleye pollock, capelin, and Pacific sand lance. The diet of humpback whales in 2004 was the most diverse, while diets in 2005 and 2006 showed a higher proportion of euphausiids. Our results reveal annual differences in humpback diets from the Kodiak region due to either individual prey preferences or prey availability. Application of a Bayesian mixing model to stable isotope analysis improves description of regional diets and comparison of these diets to resource availability and quality.

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