Orcas swim long distance for that radiant skin

Nov 7, 2011, 14:40 GMT

London - The orcas - or killer whales - of Antarctica take long detours through subtropical waters over thousands of kilometres apparently for the sake of their skins.

These whales of the species Orcinus orca could be using the warmer waters to renew their skins, according to US scientists writing in the journal Biology Letters published by Britain's Royal Society.

The warmer waters provide the opportunity to renew the skin tissue without losing too much body heat, in contrast with the frigid waters off the coast of Antarctica.

The researchers, led by John Durban of the US National Oceanic and Atmospheric Administration, suspect that beauty is not the sole objective behind the marathon swims. The whales' general health is also at stake.

The team fitted 12 orcas with transmitters and monitored their peregrinations over the course of two years. The routes charted showed that five of the whales headed purposefully to the warmer waters off Uruguay and Brazil.

The speed at which they swam to the warmer waters was remarkable. One whale returned to the cold of Antarctica after just 42 days, having travelled 9,400 kilometres - or 224 kilometres a day.

There appears to have been a central aim behind the lengthy trip. Thick layers of a particular group of algae (diatoms) build up on the whale's skins in the cold waters of the Antarctic. Antarctic orcas - the species can in fact be sighted in virtually all the seas of the world - often appear yellowish as a result.

The whales are more easily able to scrub off these algae and renew their skins in warm rather than cold waters, where they would suffer greater heat loss.

If their hypothesis is confirmed, the researchers believe it could help improve the understanding of the way in which other whale species move around the world's oceans. For example, why baleen whales travel to tropical waters is still little understood.