Killer whales swim three thousand miles just to lose their skin

Every so often, the killer whales that live around Antarctica will drop everything they're doing and swim three thousand miles due north. It's an extreme journey, but the end result is the whale equivalent of a day at the spa.

Killer whales, otherwise known as orcas, need to periodically regenerate their skin in order to stay healthy. The problem for them and other polar mammals is that molting means losing a ton of body heat, which can be potentially dangerous in such frigid waters. For mammals like seals, this isn't a problem - they can just climb up onto the nearest scrap of land and molt away. But killer whales don't have that option, and so they're forced to go to some pretty extreme measures.

Researchers from the US's National Oceanic and Atmospheric Administration tracked the movements of five killer whales, all of which moved from the freezing Antarctic waters - average temperature 30 degrees Fahrenheit - to the relatively balmy subtropical waters off the coast of Brazil and Uruguay, where it's 75 degrees. One whale managed the entire 6,000 mile round trip in just 42 days.

It appears these journeys are pretty much exclusively for regenerating their skin - at those speeds, they wouldn't have enough time to go hunting or to take care of their young. It's a trip that takes the whales far outside their natural comfort zone, as evidenced by the fact that the whales went slower and slower the further north they got. But the end result is pretty much the killer whale equivalent of a deep cleanse, as they complete their epic swim just to find somewhere that they can relax and fix their skin. Rarely does a quick trip to the spa involve quite such an epic amount of work.

Biology Letters via ScienceNOW. Image by John Durbin/NOAA.