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Spatial segregation and similar trophic-level diet among eastern Canadian Arctic/north-west Atlantic killer whales inferred from bulk and compound specific isotopic analysis

Published online by Cambridge University Press:  13 November 2013

Cory J.D. Matthews  and
Steven H. Ferguson
Cory J.D. Matthews*
Affiliation:
Department of Biological Sciences, University of Manitoba, Winnipeg, MB, CanadaR3T 2N2
Steven H. Ferguson
Affiliation:
Department of Biological Sciences, University of Manitoba, Winnipeg, MB, CanadaR3T 2N2 Fisheries and Oceans Canada, 501 University Crescent, Winnipeg MB, CanadaR3T 2N6
*
Correspondence should be addressed to: C. Matthews, Department of Biological Sciences, University of Manitoba, Winnipeg, MB, CanadaR3T 2N2 email: cory_matthews@umanitoba.ca
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Abstract

Killer whales in the Eastern Canadian Arctic (ECA) prey on narwhal, beluga, bowhead whales and seals, while further south in the north-west Atlantic (NWA), killer whales off the coast of Newfoundland and Labrador prey on both marine mammals and fish. Bulk and amino acid (AA) specific isotopic composition of dentinal collagen in teeth of 13 ECA/NWA killer whales were analysed to assess the degree, if any, of dietary specialization of killer whales across the region. Dentine was sampled from within annual growth layer groups (GLGs) to construct chronological profiles of stable nitrogen (δ15N) and carbon (δ13C) isotopic compositions for individual whales spanning 3–25 years. Interannual isotopic variation across GLGs was less than that among individuals, and median bulk δ15N values differed by up to 5‰ among individuals. Significant correlation between bulk δ15N values and baseline (source AA) δ15N values indicates much of the observed isotopic variation among individuals reflects foraging within isotopically distinct food webs, rather than diet differences. This interpretation is supported by consistent differences in bulk δ13C values between the two individuals with lowest source AA δ15N values and the remaining whales. After accounting for baseline isotopic variation, comparable δ15N values among individuals indicates similar trophic-level diet, although uncertainties in relative trophic 15N enrichment of individual AAs currently limits trophic position estimates for top consumers. Further research is required to clarify seasonal movement patterns and possible diet shifts of ECA/NWA killer whales to better define their role in marine ecosystems across the region.

Keywords

Orcinus orcadentinegrowth layer groupsstable isotope analysisnitrogencarbonamino acidsmarine mammalsdistribution

Information

Type
Research Article
Information
Journal of the Marine Biological Association of the United Kingdom , Volume 94 , Issue 6 , September 2014 , pp. 1343 - 1355
Copyright
Copyright © Marine Biological Association of the United Kingdom 2013 

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