Penguins Changed Diet Due to Whaling, Study Suggests

John Roach
for National Geographic News
July 20, 2007
Extensive whale and seal hunting in Antarctica over the past 200 years appears to have triggered a shift in the diet of Adélie penguins, a new study suggests.

The seabirds abandoned fish in favor of krill, shrimp-like crustaceans that are a major component in the diets of fur seals and baleen whales.

The finding supports a theory that Antarctic sealing and whaling led to a krill population explosion, and the penguins apparently took advantage of the surplus.

"We have some pretty good direct data that penguins were switching to krill when it became highly available," said Steve Emslie, a biologist at the University of North Carolina in Wilmington.

Emslie is the co-author of a paper on the findings reported earlier this month in the journal Proceedings of the National Academy of Sciences.

Penguin Fossils

Emslie and colleague William Patterson of the University of Saskatchewan, Canada, based the finding on analysis of more than 220 fossil eggshell fragments ranging from the past 100 to 38,000 years.

The proportions of certain forms of carbon and nitrogen in the eggshells tell the researchers what type of food the penguins ate in the days before laying their eggs.

For most of the past 38,000 years, the penguins ate a variable diet heavy on fish, which are higher up the food chain than krill. The birds changed to krill a few centuries ago.

"This implies a huge ecological dietary response by the penguins in relation to some change in their environment," Keith Hobson of Environment Canada, the nation's environment agency, commented in an email.

The dietary shift coincides with the advent of whaling and sealing in the region, suggesting the sudden abundance of easier-to-catch krill was a preferable high-energy food source, Emslie said.

Hobson, who was not part of the research, said such an explanation is plausible but only makes sense if accompanied by a reduction in fish supply.

"Why does it matter that krill became more abundant to a predator that for 8,000 years happily made eggs from fish?" he noted.

Further research, he added, should focus on the scarcity of fish rather than the abundance of krill.

Warming Trends

Whatever caused the switch, the eggshells show a switch occurred, according to the analysis.

"And now with krill on a decline and fish harvested out in a lot of areas … that's a concern," Emslie said.

"What do [the penguins] have left to switch to? They don't really have any options left."

Krill populations are dwindling, especially on the Antarctic Peninsula, where warming temperatures mean less sea ice. Sea ice holds algae that the krill feed on when it melts.

(Read a related story about melting glaciers on the Antarctic Peninsula.)

In addition, fishers are now actively taking krill, which are used as feed in fish farms. This "will further cause problems," he said.

According to Hobson, the "good news" from the research is how adaptable Adélie penguins are to environmental changes.

"Although I remain a pessimist when it comes to how they may cope with the onslaught of climate change," he added.

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