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

Journal article
Authors Emily K. Brault
Paul L. Koch
Daniel P. Costa
Matthew D. McCarthy
Luis A. Hückstädt
Kimberly T. Goetz
Kelton W. McMahon
Michael E. Goebel
Olle Karlsson
Jonas Teilmann
Tero Harkonen
Karin C. Harding
Published in Marine Ecology Progress Series
Volume 611
Pages 1-18
ISSN 0171-8630
Publication year 2019
Published at Department of Biological and Environmental Sciences
Pages 1-18
Language en
Keywords Amino acids, Antarctica, Compound-specific isotopes, Crabeater, Foraging ecology, Ross seal, Seal, Trophic dynamics, Weddell seal
Subject categories Biological Sciences


© The authors 2019. 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.

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