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Pacific sleeper shark Somniosus pacificus trophic ecology in the eastern North Pacific Ocean inferred from nitrogen and carbon stable-isotope ratios and diet

Authors

  • D. L. Courtney,

    Corresponding author
    1. School of Fisheries and Ocean Sciences, Juneau Center, University of Alaska Fairbanks, 17101 Point Lena Loop Road, Juneau, AK 99801, U.S.A.
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  • R. Foy

    1. Kodiak Laboratory, Resource Assessment and Conservation Engineering Division, Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA, 301 Research Court, Kodiak, AK 99615, U.S.A.
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Author to whom correspondence should be addressed at present address: Southeast Fisheries Science Center, National Marine Fisheries Service, NOAA, 3500 Delwood Beach Road, Panama City, FL 32408, U.S.A. Tel.: +1 850 234 6541; email: dean.courtney@noaa.gov

Abstract

Stable-isotope ratios of nitrogen (δ15N) and lipid-normalized carbon (δ13C′) were used to examine geographic and ontogenetic variability in the trophic ecology of a high latitude benthopelagic elasmobranch, the Pacific sleeper shark Somniosus pacificus. Mean muscle tissue δ13C′ values of S. pacificus differed significantly among geographic regions of the eastern North Pacific Ocean. Linear models identified significant ontogenetic and geographic variability in muscle tissue δ15N values of S. pacificus. The trophic position of S. pacificus in the eastern North Pacific Ocean estimated here from previously published stomach-content data (4·3) was within the range of S. pacificus trophic position predicted from a linear model of S. pacificus muscle tissue δ15N (3·3–5·7) for fish of the same mean total length (LT; 201·5 cm), but uncertainty in predicted trophic position was very high (95% prediction intervals ranged from 2·9 to 6·4). The relative trophic position of S. pacificus determined here from a literature review of δ15N by taxa in the eastern North Pacific Ocean was also lower than would be expected based on stomach-content data alone when compared to fishes, squid and filter feeding whales. Stable-isotope analysis revealed wider variability in the feeding ecology of S. pacificus in the eastern North Pacific Ocean than shown by diet data alone, and expanded previous conclusions drawn from analyses of stomach-content data to regional and temporal scales meaningful for fisheries management.

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