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MEPS 611:1-18 (2019)  -  DOI: https://doi.org/10.3354/meps12856

FEATURE ARTICLE
Trophic position and foraging ecology of Ross, Weddell, and crabeater seals revealed by compound-specific isotope analysis

Emily K. Brault1,*, Paul L. Koch2, Daniel P. Costa3, Matthew D. McCarthy1, Luis A. Hückstädt3, Kimberly T. Goetz4, Kelton W. McMahon5, Michael E. Goebel6, Olle Karlsson7, Jonas Teilmann8, Tero Harkonen7,9, Karin C. Harding10

1Ocean Sciences Department, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
2Earth and Planetary Sciences Department, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
3Ecology and Evolutionary Biology, University of California, Santa Cruz, 100 Shaffer Road, Santa Cruz, CA 95064, USA
4National Institute of Water and Atmospheric Research, 301 Evans Bay Parade, Wellington 6021, New Zealand
5Graduate School of Oceanography, University of Rhode Island, 215 S Ferry Rd, Narragansett, RI 02882, USA
6Antarctic Ecosystem Research Division, NOAA Fisheries, Southwest Fisheries Science Center, 8901 La Jolla Shores Dr., La Jolla, CA 92037, USA
7Department of Environmental Research and Monitoring, Swedish Museum of Natural History, Box 50007, 104 05 Stockholm, Sweden
8Department of Bioscience - Marine Mammal Research, Aarhus University, Frederiksborgvej 399, 4000 Roskilde, Denmark
9Martimas AB, Höga 160, 442 73 Kärna, Sweden
10Department of Biological and Environmental Sciences, University of Gothenburg, Box 463, 405 30 Gothenburg, Sweden
*Corresponding author:

ABSTRACT: Ross seals Ommatophoca rossii are one of the least studied marine mammals, with little known about their foraging ecology. Research to date using bulk stable isotope analysis suggests that Ross seals have a trophic position intermediate between that of Weddell Leptonychotes weddellii and crabeater Lobodon carcinophaga seals. However, consumer bulk stable isotope values not only reflect trophic dynamics, but also variations in baseline isotope values, which can be substantial. We used compound-specific isotope analysis of amino acids (CSI-AA) to separate isotopic effects of a shifting baseline versus trophic structure on the foraging ecology of these ecologically important Antarctic pinnipeds. We found that Ross seals forage in an open ocean food web, while crabeater and Weddell seals forage within similar food webs closer to shore. However, isotopic evidence suggests that crabeater seals are likely following sea ice, while Weddell seals target productive areas of the continental shelf of West Antarctica. Our CSI-AA data indicate that Ross seals have a high trophic position equivalent to that of Weddell seals, contrary to prior conclusions from nitrogen isotope results on bulk tissues. CSI-AA indicates that crabeater seals are at a trophic position lower than that of Ross and Weddell seals, consistent with a krill-dominated diet. Our results redefine the view of the trophic dynamics and foraging ecology of the Ross seal, and also highlight the importance of quantifying baseline isotope variations in foraging studies.


KEY WORDS: Ross seal · Weddell seal · Crabeater seal · Compound-specific isotopes · Amino acids · Antarctica · Foraging ecology · Trophic dynamics


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Cite this article as: Brault EK, Koch PL, Costa DP, McCarthy MD and others (2019) Trophic position and foraging ecology of Ross, Weddell, and crabeater seals revealed by compound-specific isotope analysis. Mar Ecol Prog Ser 611:1-18. https://doi.org/10.3354/meps12856

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