Krill and Whales in Antarctica
The humpback whale is a species of baleen whale. Adults range in length from 39â€“52 feet and weigh approximately 79,000 pounds. Like other large whales, the humpback was and is a target for the whaling industry. Due to over-hunting, its population fell by an estimated 90% before a whaling moratorium was introduced in 1966. Stocks have since partially recovered. There are at least 80,000 humpback whales worldwide. Scientists have recently 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.
Krill is the common name given to the small invertebrates that are found in all oceans of the world. The common name krill comes from the Norwegian word krill meaning young fry of fish.
Krill are considered an important near bottom of the food chain connection because they feed on phytoplankton and to a lesser extent zooplankton, converting these into a form suitable for many larger animals for whom krill makes up the largest part of their diet. In the Southern Ocean, one species, the Antarctic krill, Euphausia superba, makes up an estimated biomass of over 500,000,000 tons, roughly twice that of all humans. Of this, over half is eaten by whales, seals, penguins, squid and fish each year.
Advancing winter sea ice used to cover much of the Antarctica peninsulaâ€™s bays and fjords by May, protecting krill and forcing humpback whales to migrate elsewhere to find food, 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.
"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 bayâ€™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," says Ari S. Friedlaender, co-principal investigator on the project and research scientist at Duke.
Around the Western Antarctic Peninsula, krill migrate in austral autumn from open ocean waters to phytoplankton-rich bays and fjords, where juveniles feed and the population overwinters under the protective cover of ice. There is a correlation between the amount of sea ice and the amount of krill that survive the long, harsh Antarctic winter. "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 canâ€™t replenish themselves," Friedlaender says.
Scientists already have documented drops in krill abundance over the last 50 years related to reduced sea ice cover. Seals and penguins have a relatively small foraging range, and some canâ€™t eat any prey other than krill or hunt without the presence of sea ice. Whales can migrate longer distances and might be able to find food elsewhere, but may be affected in other ways.
"Weâ€™re starting to hear songs being produced by whales in the Antarctic â€“ sexual advertisements typically heard only in humpback breeding grounds that are located thousands of miles away from these bays," Friedlaender says.
Humpback whales typically reproduce once every three years, "so if a female doesnâ€™t have to go to the breeding grounds every year â€“ if she has access to food here and isnâ€™t being forced out by sea cover â€“ why should she leave?" Nowacek says. The presence of more females, coupled with access to a nightly krill feast, entices more males to stick around too. "So this may affect the timing and location of humpback breeding and other important life cycle events."
What is happening is a change in the existing ecosystem. What it will become is yet to be determined.
For further information: http://www.nicholas.duke.edu/news/record-number-of-whales-krill-found-in-the-antarctic-bays