How important are baleen whales as prey for killer whales (Orcinus orca) in high latitudes?
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Abstract
Transient-type killer whales (Orcinus orca) feed primarily or exclusively on
marine mammals, however, whether large whales represent an important prey source for
killer whales has been debated. A recent hypothesis by Springer et al. (2003) suggested
that overexploitation of large whales by industrial whaling forced killer whales to prey
switch from baleen whales to pinnipeds and sea otters, resulting in population declines
for these smaller marine mammals in the North Pacific and southern Bering Sea. This
prey-switching hypothesis is contingent upon the idea that killer whales regularly attack
mysticetes while they are in these high-latitude areas. In this study, I used photographic
and sighting data from baleen whales in twenty-four regions worldwide to determine the
proportion of whales that bear scars ( rake marks) from killer whale attacks and to
examine the timing of scar acquisition. The results of this study show that there is
considerable geographic variation in the proportion of whales with rake marks, however,
in every region, the vast majority of the scars seen were present on the whales' bodies by
the time the animals were first sighted. This would indicate that most killer whale attacks
on baleen whales target young animals, possibly calves on their first migration from the
low-latitude breeding and calving areas to the high-latitude feeding areas. This study
suggests that baleen whales are not important prey for killer whales in high latitudes and
that the picture of the marine ecosystem proposed by the prey-switching hypothesis is
incomplete and inaccurate.
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