Title
Geographic variation in killer whale attacks on humpback whales in the North Pacific: Implications for predation pressure
Author(s)
Steiger G.H., Calambokidis J., Straley J.M., Herman L.M., Cerchio S., Salden D.R., Urban-R. J., Jacobsen J.K., von Ziegesar O., Balcomb K.C., Gabriele C.M., Dahlheim M.E., Uchida S., Ford J.K.B., de Guevara-P. P.L., Yamaguchi M., Barlow J.
Published
2008
Publisher
Endangered Species Research
Abstract
We examined the incidence of rake mark scars from killer whales Orcinus orca on the flukes of humpback whales Megaptera novaeangliae throughout the North Pacific to assess geographic variation in predation pressure. We used 3650 identification photographs from 16 wintering or feeding areas collected during 1990 to 1993 to determine conservative estimates in the percentage of whales with rake mark scarring. Dramatic differences were seen in the incidence of rake marks among regions, with highest rates on wintering grounds off Mexico (26 vs. 14 % at others) and feeding areas off California (20 vs. 6% at others), 2 areas between which humpback whales migrate. Although attacks are rarely witnessed, the prevalence of scars demonstrates that a substantial portion of animals are attacked, particularly those that migrate between California and Mexico. Our data also suggest that most attacks occur at or near the wintering grounds in the eastern North Pacific. The prevalence of attacks indicates that killer whale predation has the potential to be a major cause of mortality and a driving force in migratory behavior; however, the location of the attacks is inconsistent with the hypothesis that animals migrate to tropical waters to avoid predation. Our conclusion is that, at least in recent decades, attacks are made primarily on calves at the winteiing grounds; this contradicts the hypothesis that killer whales historically preyed heavily on large whales in high-latitude feeding areas in the North Pacific. © Inter-Research 2008.
Keywords
geographical variation; migratory behavior; mortality risk; predation; whale; Pacific Ocean; Pacific Ocean (North); Animalia; Cetacea; Megaptera; Megaptera novaeangliae; Orcinus orca; Trematoda
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PUB12036