DURHAM, N.C. Scientists have observed a "super-aggregation" of more than 300 humpback whales gorging on the largest swarm of Antarctic krill seen in more than 20 years in bays along the Western Antarctic Peninsula.
The sightings, made in waters still largely ice-free deep into austral autumn, suggest the previously little-studied bays are important late-season foraging grounds for the endangered whales. But they also highlight how rapid climate change is affecting the region.
The Duke University-led team tracked the super-aggregation of krill and whales during a six-week expedition to Wilhelmina Bay and surrounding waters in May 2009. They published their findings today (April 27) in the online science journal PLoS ONE.
"Such an incredibly dense aggregation of whales and krill has never been seen before in this area at this time of year," says Duke marine biologist Douglas Nowacek. Most studies have focused on whale foraging habitats located in waters farther offshore in austral summer.
Nowacek and his colleagues observed 306 humpback whales or about 5.1 whales per square kilometer, the highest density ever recorded in Wilhelmina Bay. They measured the krill biomass at about 2 million tons. Small, floating fragments of brash ice covered less than 10 percent of the bay. The team returned in May 2010 and recorded similar numbers. Smaller but still higher-than-normal counts were also reported in neighboring Andvord Bay.
Advancing winter sea ice used to cover much of the peninsula's bays and fjords by May, protecting krill and forcing humpback whales to migrate elsewhere to find food, Nowacek says. But rapid climate change in the area over the last 50 years has significantly reduced the extent, and delayed the annual arrival, of the ice cover, says Nowacek, who is the Repass-Rodgers University Associate Professor of Conservation Technology.
"The lack of sea ice is good news for the whales in the short
|Contact: Tim Lucas|