Abstract
Killer whales (Orcinus orca) are important predators in high latitudes, where their ecological impact is mediated through their movements. We used satellite telemetry to provide the first evidence of migration for killer whales, characterized by fast (more than 12 km h−1, 6.5 knots) and direct movements away from Antarctic waters by six of 12 type B killer whales tagged when foraging near the Antarctic Peninsula, including all tags transmitting for more than three weeks. Tags on five of these whales revealed consistent movements to subtropical waters (30–37° S) off Uruguay and Brazil, in surface water temperatures ranging from −1.9°C to 24.2°C; one 109 day track documented a non-stop round trip of almost 9400 km (5075 nmi) in just 42 days. Although whales travelled slower in the warmest waters, there was no obvious interruption in swim speed or direction to indicate calving or prolonged feeding. Furthermore, these movements were aseasonal, initiating over 80 days between February and April; one whale returned to within 40 km of the tagging site at the onset of the austral winter in June. We suggest that these movements may represent periodic maintenance migrations, with warmer waters allowing skin regeneration without the high cost of heat loss: a physiological constraint that may also affect other whales.
Highlights
Killer whales (Orcinus orca) are important marine predators, especially in high latitudes, where energetic calculations suggest that their high caloric requirements could significantly impact slowly reproducing prey populations [1]
In coastal waters of the Antarctic Peninsula where the whales were observed hunting [9,10], movements were characterized by frequent changes in direction and relatively low net displacement; velocities averaged between 3 and 4.7 km h21 and sea surface temperature (SST) ranged from 21.98C to 2.98C
Despite frequent sightings in Antarctic waters, there have been very few records of type B killer whales occurring elsewhere [8]. Suggest that they regularly travel to the subtropics, providing the first documentation of directed, long distance migration for killer whales anywhere
Summary
Killer whales (Orcinus orca) are important marine predators, especially in high latitudes, where energetic calculations suggest that their high caloric requirements could significantly impact slowly reproducing prey populations [1]. In Antarctic waters, where killer whales are abundant [2], predation by them may be a major force structuring marine communities [3,4]. Their ecological impact must be mediated by their movement and residency patterns, which are largely unknown in this region [5]. Killer whales are known to range over thousands of kilometres [6,7], to date there is little direct evidence of seasonal or regular long-distance migrations anywhere, including Antarctica [8]. The evidence suggests that these movements were not for breeding or feeding purposes, and we hypothesize that they might be physiologically adaptive
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