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Marine Ecology Progress Series

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MEPS 665:217-231 (2021)  -  DOI:

Killer whale movements on the Norwegian shelf are associated with herring density

Emma F. Vogel1,*, Martin Biuw2, Marie-Anne Blanchet1,8, Ian D. Jonsen3, Evert Mul1, Espen Johnsen2, Solfrid Sætre Hjøllo4, Morten Tange Olsen5, Rune Dietz6, Audun Rikardsen1,7

1UiT - The Arctic University of Norway, Faculty of Biosciences, Fisheries and Economics, 9037 Tromsø, Norway
2Institute of Marine Research, FRAM—High North Research Centre for Climate and the Environment, 9007 Tromsø, Norway
3Macquarie University, Department of Biological Sciences, Sydney, New South Wales 2109, Australia
4Institute of Marine Research Box 1870 Nordnes, 5817 Bergen, Norway
5University of Copenhagen, Globe Institute, 1353 Copenhagen, Denmark
6Aarhus University, Institute for Bioscience, Marine Mammal Research, Frederiksborgvej 399, 4000 Roskilde, Denmark
7 Norwegian Institute for Nature Research, Hjalmar Johansen gate 14, 9007 Tromsø, Norway
8Present address: Norwegian Polar Institute FRAM—High North Research Centre for Climate and the Environment, 9007 Tromsø, Norway
*Corresponding author:

ABSTRACT: Killer whales Orcinus orca have a cosmopolitan distribution with a broad diet ranging from fish to marine mammals. In Norway, killer whales are regularly observed feeding on overwintering Norwegian spring-spawning (NSS) herring Clupea harengus inside the fjords. However, their offshore foraging behavior and distribution are less well understood. In particular, it is not known to what degree they rely on the NSS herring stock when the herring move to deeper offshore waters. Satellite telemetry data from 29 male killer whales were analyzed to assess whether their offshore foraging behavior is linked to herring distribution. Unlike most marine predator-prey studies that use indirect proxies for prey abundance and distribution, our study utilized 2 herring density estimates based on (1) direct observations from acoustic trawl survey data and (2) simulations from a fully coupled ecosystem model. Mixed effects models were used to infer the effect of herring density and light intensity on whale movement patterns. Our results suggest that killer whales follow NSS herring over long distances along the coast from their inshore overwintering areas to offshore spawning grounds. All whales changed from fast, directed, to slow, non-directed movement when herring density increased, although individuals had different propensities towards movement. Our data indicated that whales continue to feed on herring along the Norwegian shelf. We conclude that NSS herring constitute an important prey resource for at least some killer whales in the northeastern Atlantic, not only during the herring overwintering period, but also subsequently throughout the herring spawning migration.

KEY WORDS: Move persistence · Foraging · Habitat · Spatial ecology · Orcinus orca · Clupea harengus · Predator-prey

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Cite this article as: Vogel EF, Biuw M, Blanchet MA, Jonsen ID and others (2021) Killer whale movements on the Norwegian shelf are associated with herring density. Mar Ecol Prog Ser 665:217-231.

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