NOAA researchers offer a novel explanation for why a type of Antarctic killer whale performs a rapid migration to warmer tropical waters in a paper published this month in the science journal Biology Letters.

One tagged Antarctic killer whale monitored by satellite traveled over 5,000 miles to visit the warm waters off southern Brazil before returning immediately to Antarctica just 42 days later. This was the first long distance migration ever reported for killer whales.

"The whales are traveling so quickly, and in such a consistent track, that it is unlikely they are foraging for food or giving birth," said John Durban, lead author from NOAA's Southwest Fisheries Science Center in La Jolla, California.

"We believe these movements are likely undertaken to help the whales regenerate skin tissue in a warmer environment with less heat loss."

As evidence, the researchers point to the yellowish coating on Antarctic killer whales caused by a thick accumulation of diatoms or algae on the outer skin of the animals. The coloring is noticeably absent when they return from warmer waters indicating the upper epidermis of the skin has been shed.

The scientists tagged 12 Type B killer whales (seal-feeding specialists) near the Antarctic Peninsula and tracked 5 that revealed consistent movement to sub-tropical waters.

The whales tended to slow in the warmest waters although there was no obvious interruption in swim speed or direction to indicate calving or prolonged feeding.

"They went to the edge of the tropics at high speed, turned around and came straight back to Antarctica, at the onset of winter", said Robert Pitman, co-author of the study. "The standard feeding or breeding migration does not seem to apply here".

Researchers believe there are at least three different types of killer whales in Antarctica and have labeled them Types A, B and C.