09 March 2011

Penguin population shifts due to fishy factors?

ANTARCTICA - There's something fishy going on with the Adelie penguin populations in the Ross Sea region. Ecologist David Ainley, principal investigator for a long-term project trying to understand penguin population response to climate and ecosystem change, told the Antarctic Sun he is concerned that a toothfish fishery that operates in the Ross Sea may skew data collected by climate change researchers.

With the exception of the Cape Royds colony, which suffered a population crash after icebergs carved off the Ross Ice Shelf in 2000 and massively extended the penguins' journeys to the open sea, Adelie penguin colonies in the Ross Sea region have grown tremendously. Cape Crozier, possibly the largest Adelie penguin colony in the world, now has an estimated 230,000 breeding pairs; that's an increase of nearly 50,000 breeding pairs in the last decade. The nearby Beaufort Island colony has expanded from 40,000 to 55,000 breeding pairs.

While population increases like these should be good news, a possible explanation for them is not good: industrial fishing. In the 1996-97 austral summer, an Antarctic toothfish fishery began operating in the region. In less than a decade, scientists who had been successfully capturing and releasing Antarctic toothfish, known to consumers as "Chilean seabass", in McMurdo Sound for research since the 1970s could no longer find any. Research has shown that, at the same time, Ross Sea killer whales, which prey on toothfish, have decreased in occurence frequency. And there have been these increases in the populations of Adelie penguins, which compete with toothfish for food.

Ainley and others have argued that too little is known about toothfish, and Ainley said it was unwise to allow the fishery to operate without learning more about them. He told the Antarctic Sun that he believes the fishery may be taking too big a bite out of the toothfish population, and that although a lot of people would want to discount it, the fishery may be behind the apparent shift in populations of toothfish, penguins and whales.

While there are other environmental factors involved in the penguin population increases, such as the immigration of Cape Royds penguins who abandoned their colony in the "tough iceberg years" to neighbouring colonies, Ainley said immigration from Cape Royds cannot explain the rapid expansion of the other Ross Sea colonies.

"Just as when thousands of food-competing Antarctic minke whales were removed from the wintering area of Ross Sea penguins during the 1970s, Adelies are exhibiting a spurt of colony growth not easily explained by climate change," he told the Antarctic Sun.

Ainley is concerned that researchers like himself who are studying the effects of climate change on the marine ecosystem may have their data skewed by the fishery. He asked, "You're either studying climate change or you’re studying fish depletion, so what are you going to study?"

Source
Population pressures by Peter Rejcek, 18 February 2011, The Antarctic Sun

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