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Prey switching by killer whales in the north-east Atlantic: observational evidence and experimental insights

Published online by Cambridge University Press:  17 December 2013

Dag Vongraven*
Affiliation:
Norwegian Polar Institute, Fram Center, N-9296 Tromsø, Norway
Anna Bisther
Affiliation:
Reportagebörsen, Kronhusgatan 2F, S-41113 Gothenburg, Sweden
*
Correspondence should be addressed to: D. Vongraven, Norwegian Polar Institute, Fram Center, N-9296 Tromsø, Norway email: [email protected]

Abstract

Studies in the Pacific have identified distinct killer whale ecotypes that are either specialized mammal- or fish-eaters. The different types have developed hunting strategies that would suggest specialization could be more advantageous than generalism. However, it has been suggested, based on long-term dietary markers of tooth wear and stable isotope values, that lineages in the North Atlantic are generalist, but with individual variation in the proportion of prey types consumed. Here, we present the results of ten years of observational and photo-identification data of a population of killer whales that follows the Norwegian spring-spawning stock of Atlantic herring. Although the whales were predominantly observed while feeding upon herring, one pod of herring-eating whales was also observed interacting with seals. This supports the hypothesis based on the long-term markers, of a degree of specialization, with a small number of groups persistently feeding upon mammals, but switching between herring and seals. We further investigated this prey switching by conducting playbacks of herring-eating killer whale sounds to harbour seals at haul-out sites on the herring spawning grounds. We recorded changes in behaviour consistent with an anti-predator response, suggesting the seals perceived the herring-eating killer whales as a potential predatory threat and had not habituated to their calls. This could be due to the risk of herring-eating killer whales switching to mammalian prey, or the difficulty of discriminating between killer whale pods due to the large population size and number of killer whale call dialects in this population, or a combination of both.

Type
Research Article
Copyright
Copyright © Marine Biological Association of the United Kingdom 2013 

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