Whale wanders off the beaten path
Migrating humpbacks sometimes switch oceans.
The wandering ways of a juvenile humpback whale (Megaptera novaeangliae) who moved into a different ocean have bolstered the idea that humpbacks are not locked into one learned migratory route for their whole lives.
Humpbacks make huge migrations, sometimes swimming more than 8,000 kilometres twice a year. They spend their summers feasting in the polar regions, and their winters breeding in the tropics.
Infant whales are thought to learn their route from their mother and tend to stick with it for life. This means that groups of whales with different routes have different gene pools and, often, different trademark songs. But previous studies of whale genetics have indicated that there must be some mixing between such groups.
Cristina Pomilla and Howard Rosenbaum of the American Museum of Natural History in New York have identified one whale that has contributed to this mixing, by wintering in the Indian Ocean near Madagascar in 2000 and then turning up on the other side of Africa in the Atlantic near Gabon in the winter of 2002.
"It is lucky that we were there for both events," says Pomilla, who spent several winters in a boat shooting crossbows at humpbacks. The darts were modified to take a little sample of skin about the size of a fingertip. Pomilla says this doesn't hurt the whales. "It is probably like a mosquito bite for a human."
The skin samples were used to gather DNA, which was then used to compare whales by looking at eleven highly variable sections called microsatellites. They worked with 1,202 skin samples, collected over six years from the two wintering grounds, and found just one match where all eleven microsatellites were identical in samples from different oceans. When they pulled up snapshots of the dorsal fins that went with each sample, they found they were the same.
The finding, which is reported in this week's Royal Society journal Biology Letters, might make it more difficult for managers aiming to set hunting quotas for the whales in the future1.
Traditionally, a number of expendable whales is determined for each group separately. But if some whales are hopping from area to area between years, they could be counted twice in group census studies, overestimating the populations.
The big mystery is why the whale switched oceans. Was he looking for new mating opportunities, or was he just lost? Phillip Clapham, a marine biologist at the National Marine Mammal Laboratory in Seattle, Washington, suggests that it could be both. "If you're on a highway heading to a singles bar and you take a wrong turn, but find a different hangout, then you may as well hit on whoever's there anyway."
- Pomilla C. & Rosenbaum H. Biology Letters, Doi:10.1098/rsbl.2005.0351 (2005).