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Antarctica Whale

Alison Stimpert / University of Hawaii

Duke researcher Ari Friedlaender tags a whale during his research in Wilhelmina Bay, Antarctica.

Whale of a find: Krill feast in Antarctica?

by Janelle Schroeder
April 27, 2011

Antarctica Whale 2

Ari Friedlaender / Duke University Marine Laboratory

A humpback whale plays in the icy waters of the Western Antarctic Peninsula.

The surprise discovery of the largest cluster of Antarctic krill in over 20 years and the highest distribution per kilometer of humpback whales in the Western Antarctica Peninsula has left researchers stunned.

The super aggregation of krill, small shrimp-like organisms, located in Wilhelmina Bay was estimated to have a total biomass of 2 million tons – the largest recorded cluster of krill in more than two decades according to the study published today in the online science journal PLoS ONE.

“We didn’t anticipate the concentration of krill and whales we found,” said Ari Friedlaender, research scientist for Duke University Marine Laboratory in Beaufort, S.C. He said that the krill looked like a massive wet blob taking over the computer screen of their scanning equipment. “From the surface to 300 meters below was constant krill.”

The research team also used the maximum memory in their software package that tracked the whales. In all, 146 sightings of 306 whales were recorded over a 100 square kilometer area. It was the largest number of whales sighted on such a large scale. The team returned the next year and recorded similar results.

The sightings in May 2009 and 2010 suggest that both shallower bodies of water and the transition into winter play a vital role in the correlation between krill and whales during the autumn months.

“Most of the research that goes on around the peninsula takes place from December through March – in high summer,” said Friedlaender. “That transition into winter is very important.”

Duke research marine biologist Douglas Nowacek, along with Friedlaender and a team of scientists, first tracked both the Antarctic krill and humpback whales during a six-week expedition to Wilhelmina Bay.

During the expedition there was little sea ice present in Wilhelmina Bay. According to the study, sea ice covered less than 10 percent of the bay.

The short-term effects of a krill super aggregation are positive for Antarctic predators. Krill-consuming animals can take advantage of the super aggregation in the bays during the autumn months before an incoming layer of sea ice forces the animals out of the area for the winter, said Friedlaender.

The long-term effects, however, suggest a strong negative effect on the krill population. According to Friedlaender, the large number of krill discovered during their expedition is not sustainable in the long term.

Fewer krill young will be produced over time without the necessary sea ice, which will lead to a major change in the availability of krill, he said.

Krill is a vital part of the Antarctica ecosystem. They are both an active food source for Antarctic predators as well as a harvested food source for farm-raised salmon. Krill migrate from open waters to bays and fjords in the autumn, seeking a protective layer of sea ice that feeds juvenile krill and shelters adult krill.

Scientists have already found a drop in krill abundance over the last 50 years. The drop is related to rapid climate change and a reduced amount of sea ice cover, researchers said.

The lack of a sea ice cover is one of the biggest climate change issues facing the Western Antarctic Peninsula. According to assistant professor Sharon Stammerjohn at the University of California, Santa Cruz, the western side has a maritime climate that is moderated more by the ocean, meaning that the west side is feeling the changes more dramatically.

“The dramatic sea ice loss is due to wind-driven changes, primarily responding to climate change,” said Stammerjohn, who was not involved with the study. “The sea ice is not changing because it’s warmer, not directly anyway.”

She also analyzed satellite images over a 26-year period that revealed a shortening of the sea ice season by 85 days – nearly three months. These large changes are happening in the southern part of the peninsula. The farther north the sea ice occurs, the number of sea ice days that are lost due to climate change lessens.

“The key thing for krill and whales is focusing on the seasonality,” said Stammerjohn. “The point being that most of the changes are happening in the autumn.”

If the krill population further deteriorates, other species face potential consequences. Seals and penguins have a relatively small feeding area and without krill in their immediate area, their food supply is limited. Some species, such as Adélie penguins, only eat krill.

The life cycles of whales and krill have evolved over time and the life histories of these animals are attuned to seasonal cycle.

Stammerjohn said, “If you start changing that, that’s where you are going to have your biggest impact.”