Seasonal movements of killer whales between Iceland and Scotland

Abstract

Understanding the movements and distribution of killer whales Orcinus orca is important for evaluating the threats they face, as well as their impact as top predators in different ecosystems. Killer whales in the Northeast Atlantic are thought to follow specific prey stocks but their seasonal movements are still poorly understood. Here, we used recent killer whale photographic data collected in Iceland and Scotland to show that some individual whales repeatedly move between these locations. Unlike other killer whales that appear to follow the movements of particular herring stocks, the whales we studied appear to feed on the Icelandic summer-spawning herring stock in winter, and then move outside the summer distribution range of this herring stock. Based on these new photographic recaptures and previously published movements of killer whales between Iceland and Scotland, we infer that movements between both locations have been occurring for several years at least. Although based on only 7 identified individuals, our results provide the first evidence of regular seasonal movements between Iceland and Scotland, and suggest individual or group variability in the movement patterns of killer whales that prey on herring. Understanding killer whale movements will aid our understanding of prey specialization, the whales’ potential impacts on local prey resources, and their susceptibility to fluctuations in the availability of different prey species.