Killer whales migrate - but why?

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Killer whales undertake spa vacations that involve round trip journeys of thousands of miles, reveals research to be published in a forthcoming issue of the journal Biology Letters.

Using satellite tagging of 12 type B Killer whales in Antractica, John Durban and Robert Pitman demonstrated that some of the cetaceans undertook seasonal long-distance migrations to warmer subtropical waters off the coasts of Uruguay and southern Brazil.

The authors found six of the 12 whales that were tagged began to move very rapidly out of Antarctic waters, swimming from waters with surface temperatures of -1.9°C to those of 24.2°C. The journeys were apparently made in some haste, with one whale completing a 5075-nautical mile (9400-km) round-trip journey in 42 days.

Although the whales travelled slower when reaching warmer waters, there was no obvious interruption in swim speed or direction to indicate giving birth or prolonged feeding.

The authors believe movements are undertaken to help the whales regenerate skin tissue in a warmer environment with less heat loss. The fact that the journeys were undertaken without any seasonal rhythm (they were initiated over a period of 80 days between February and April) supported this hypothesis.

Further support for this hypothesis comes from the fact that Killer whales in Antarctica are often coloured yellow because of a thick accumulation of diatoms on their skin. The same individuals appear to be ‘clean’ at other times, and the authors infer that had just retuned from subtropical waters, where they shed their diatoms while replacing their epidermal tissue.

The authors surmise that Baleen whales may undertake similar migrations to warmer waters for the same reason.

For more information, see the paper: Durban, JW and RL Pitman (2011) Antarctic killer whales make rapid, round-trip movements to subtropical waters: evidence for physiological maintenance migrations? Biology Letters doi:10.1098/rsbl.2011.0875

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