Humpbacks feast in record numbers in warmer Antarctic
April 27 2011 Lewis Smith
Record numbers of humpback whales have been recorded gorging on the biggest swarm of krill witnessed for more than two decades.
Scientists counted 306 humpbacks feeding on the krill in Wilhelmina Bay on the Western Antarctic Peninsula in May 2009.
It was calculated that there were 5.1 humpback whales for each square kilometre in the bay, making it the highest density ever recorded. The quantity of krill was estimated at 2 million tons.
Researchers returned to the bay last year and found similar numbers of the whales eating krill, suggesting the area is an important late-season feeding ground.
“Such an incredibly dense aggregation of whales and krill has never been seen before in this area at this time of year,” said Dr Douglas Nowacek, a marine biologist at Duke University, in the US.
Until recently the bay would have been inaccessible to the whales in May because it would have been frozen over but climate change over the last 50 years has meant the ice forms later in the year.
In the short term the changes mean a feeding bonanza for the whales but in the longer term it is expected to reduce the overall quantity of the crustacean. Ice protects the krill and previous research has established that the more ice there is the better they survive.
“The lack of sea ice is good news for the whales in the short term, providing them with all-you-can-eat feasts as the krill migrate vertically toward the bay’s surface each night. But it is bad news in the long term for both species, and for everything else in the Southern Ocean that depends on krill,” said Dr Ari Friedlaender, a research scientist at Duke.
“If there are more areas with large aggregations of krill hanging out in waters where sea ice has diminished, you could see a big decrease in the standing krill stock, especially if we have a few years of back-to-back bad ice and the krill can’t replenish themselves.”
Evidence that the reduced ice cover is beginning to change humpback behaviour has also emerged with the discovery that mating calls are being heard in the region for the first time on record.
Until now humpbacks have been far from Antarctica before they start breeding but the whale songs suggest that with food still plentiful some females now no longer feel the need to move away from the region before mating. The study is published in the online journal PloS ONE.
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