Saturday, October 16, 2010

Humpback whale sets travel record: researchers

A lone female humpback whale traveled more than 9,800 kilometers (more than 6,000 miles) from breeding areas in Brazil to those in Madagascar, setting a record for the longest mammal migration ever documented.

Humpback whales (Megaptera novaeangliae) are known to have some of the longest migration distances of all mammals and this huge trek is about 400 kilometers farther than the previous humpback record.

The whale's journey was unusual not only for its length, but also
because it spanned an ocean basin, multiple breeding zones and almost 90 degrees of longitude. Typically, humpbacks move between high-latitude feeding areas and low-latitude breeding grounds, without much variation in longitude — and the longest journeys recorded until now have been between breeding and feeding sites.

What's more, those that travel the farthest are usually males, whereas females are generally very loyal to their breeding sites. "The main take-home message is that the movement patterns of these animals are messier and less constrained than we tend to think," says Peter Stevick.

While the record is interesting, the findings help researchers understand the behaviors of the whales, which are endangered, Peter Stevick of the College of the Atlantic in Maine and an international team of colleagues reported.

"It is unexpected to find this exceptional long-distance movement between breeding groups by a female," they wrote in the journal Biology Letters.

"While humpback whales regularly travel 5,000 km between breeding
and feeding grounds, they are commuters, not adventurers," Stevick's team wrote in a summary of their work.

The whale, identified by her natural markings and DNA, was first seen off Brazil in August 1999.

"The whale subsequently was photographed just over two years later on 21 September 2001 from a commercial whale watch tour vessel. It was one of a trio of whales seen between Ile Sainte Marie/Nosy Boraha and the east coast of Madagascar," they wrote.

"The minimum travel distance between these locations, via a great circle route rounding Cape Agulhas and Cap Ste Marie, is greater than 9,800 km (more than 6,000 miles). This is about 4,000 km (2,500 miles) longer than any previously reported movement between breeding grounds and more than twice the species' typical seasonal migratory distance."

The scientists then estimated the animal's shortest possible route: an arc skirting the southern tip of South Africa and heading northeast towards Madagascar. The minimum distance is 9,800 kilometers, says Stevick, but this is likely to be an underestimate, because the whale probably took a detour to feed on krill in the Southern Ocean near Antarctica before reaching its destination. The researchers cannot say at this point why this whale traveled so far.

"It is the longest documented movement by a mammal, about 400 km (250 miles) longer than the longest seasonal migration that has been reported," they added.

Humpbacks rack up a lot of miles. They typically cover up to 25,000 kilometers (16,000 miles) going back and forth in a year.
"The severe depletion of humpback whales throughout the Southern Hemisphere, and apparent inconsistencies in the regional patterns of recovery, make understanding of regional movement patterns a considerable conservation concern," the researchers wrote.
Daniel Palacios, an oceanographer at the University of Hawaii at Manoa, says that the record-breaking journey could indicate that migration patterns are shifting as populations begin to recover from
near-extinction. Behaviors often change as population densities grow; for instance, animals may disperse to avoid competition for food, he says. (Left: humpback with calf)

But the real reasons for the whale's impressive trek remain a mystery. The female could have been following prey, exploring new breeding habitats, responding to distant calls, or simply wandering astray. "We generally think of humpback whales as very well studied, but then they surprise us with things like this," Palacios says. "Undoubtedly there are a lot of things we still don't know about whale migration."

Reuters, "Humpback whale sets travel record: researchers", accessed October 14, 2010
Nature, "Humpback whale breaks migration record", accessed October 14, 2010

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