A super-aggregation of whales and krill was discoverd during a six-week expedition to Wilhelmina Bay in 2009. (Photo: YouTube/FIS)
Amazing numbers of krill, whales shed light on climate change's effects
Thursday, May 05, 2011, 15:20 (GMT + 9)
Researchers have found an astonishing abundance of humpback whales (Megaptera novaeangliae) feeding on a super-aggregation of Antarctic krill (Euphausia superb). Published in the journal PLoS ONE, this comprises the largest concentration of krill discovered in over 20 years and the highest density of humpback whales ever reported.
The scientists -- from the Laboratoire d'Océanographie Physique et Biogéochimique (LOPB) of the Centre National de la Recherche Scientifique (CNRS) and the Université de la Méditerranée in France and Duke University Marine Laboratory in the US -- believe their findings can help elucidate how the Antarctic Peninsula is being influenced by climate change.
The team tracked the super-aggregation of whales and krill during a six-week expedition around Wilhelmina Bay in May 2009.
Professor of Duke University and lead author of the study Douglas Nowacek said the astounding aggregation of whales -- 306 humpback -- and krill -- 2 million tonnes -- had never been observed there at that time of year.
Researchers think advancing winter sea ice used to cover most of the peninsula by May, protecting krill stocks and sending humpback whales elsewhere for food. But rapid climate change in the last 50 years has thinned the scope of the ice and delayed its annual arrival, Nowacek said.
“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,” explained Ari Friedlaender of Duke and one of the co-authors of the study. “But it is bad news in the long term for both species, and for everything else in the Southern Ocean that depends on krill.”
The study’s authors wrote that the changes in the physical structure of the environment around the peninsula may also alter the ecological interactions among krill and their predators.
“Our observations indicate that humpback whales and their prey co-occur in super-aggregations during late autumn in the bays and fjords along the western Antarctic Peninsula (WAP). Efforts to monitor the distribution, abundance and dynamics of these whales should account for these large aggregations,” the authors continued.
The researchers will analyse how changes in the extent of sea ice modify the feeding ecology of predators including humpback whales in the short term and the dynamics of krill stocks in the long term. Concerns also exist regarding increasing commercial krill fishing.
Taking into account the effects of climate change on the aforementioned dynamics is necessary to fully comprehend changes in the biomass of Antarctic krill and to foresee the recovery of whale populations, the authors said.
- Antarctic krill biomass high in nearshore waters
- The krill paradox
By Natalia Real