A group of humpback whales seeking balmier waters have traveled a record-breaking 5,100 miles, the longest-ever documented migration undertaken by a mammal.
Humpback whales (Megaptera novaeangliae) in the Southern Hemisphere are known to migrate from their high-latitude feeding areas in polar waters, rich in shrimp-like critters, to more tropical regions during the winters for breeding.
The discovery, detailed in the April 3 online edition of the journal Biology Letters, will help clear up a debate over what drives these trans-equatorial treks and the whales' final winter destination.
Kristin Rasmussen, a biologist with the Cascadia Research Collective in Olympia, Wash., and her colleagues identified and tracked seven humpback whales, including a mother-calf pair, using distinct markings on the whales' flukes as fingerprints. The whales migrated from their Antarctic feeding waters to a wintering site off the Pacific coast of Central America.
The group clocked an average of 5,157 miles, out-swimming the previous distance champion, a humpback that jetted an estimated 4,970 miles, according to the authors of the new study.
Daniel Palacios, an oceanographer at NOAA's Southwest Fisheries Science Center laboratory in Pacific Grove, Calif., matched up sea-surface temperatures with the wintering grounds of the monitored whales and 24 other humpback wintering sites around the globe.
The results showed wintering areas coincided with warm waters, ranging from about 70 degrees Fahrenheit to 83 degrees Fahrenheit, irrespective of latitude.
This supports the idea that water temperature drives the migration and distribution of whales, the researchers say.
"It was very exciting because for years everyone said humpback whales could be found in warmer waters during the winter months, but this was the first time we were actually able to quantify this on a global scale and relate it to these long distance migrations" Rasmussen said.
The scientists note in the research paper that warm water could benefit developing whale babies: "Calf development in warm water may lead to larger adult size and increased reproductive success, a strategy that supports the energy conservation hypothesis as a reason for migration."
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