Abstract
Killer whales (Orcinus orca) have been documented preying on either fish or marine mammals in several regions, suggesting that this odontocete species has the ability to specialize on different types of prey. Off Norway, killer whales have been shown to rely on the Atlantic herring (Clupea harengus) as a main prey resource. Infrequent observations have revealed seals as an additional component of their diet, yet the extent of predation on marine mammals has remained largely unknown. Here, we present the findings of 29 years of photographic and observational data on seal-feeding killer whale groups identified in Norwegian coastal waters. Four groups have been observed preying and feeding on seals over several years, taking both harbor (Phoca vitulina) and grey (Halichoerus grypus) seals. These stable groups are shown to adopt small group sizes, were typically observed in near-shore areas and were not encountered on herring wintering grounds. Behavioral and social traits adopted by these groups are similar to those of pinniped-feeding killer whales from other regions. The potential ecological reasons and the extent of such prey specializations are discussed.
Highlights
Killer whales (Orcinus orca) are cosmopolitan apex predators, preying on over 140 prey species including bony and cartilaginous fish, squids, mammals, reptiles and birds throughout their cosmopolite range [1, 2]
A total of 23 predation events of killer whales on seal prey in Norwegian coastal waters was documented from 15,000 photographs taken over 300 days of research effort between March 1988 and June 1992 [24], and 158,000 photographs, six videos and field notes taken over 468 days between July 2010 and December 2016
Repeated observations over time of identified individuals preying on seals support persistent preference for pinniped prey over several years for K whales, and for nearly three decades for KI-03, KI-05 and KI-06
Summary
Killer whales (Orcinus orca) are cosmopolitan apex predators, preying on over 140 prey species including bony and cartilaginous fish, squids, mammals, reptiles and birds throughout their cosmopolite range [1, 2]. Some local populations feed on a narrow range of prey, adapting feeding strategies to prey type and availability [3,4,5,6]. The so-called resident type appears to be exclusively fish-feeding, preferentially preying on salmon species, whereas the transient type preys exclusively on marine-mammals [4, 10, 12, 14].
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