Penguin Diet Change Caused by People?

July 9, 2007 — Around 200 years ago, a group of Antarctic penguins started a dramatic new diet: they switched from eating mostly big fish to a diet of tiny crustaceans.

And, new research suggests, humans might have forced the change.

Researchers Steven Emslie and William Patterson analyzed more than 220 fossilized penguin eggshells ranging in age from 100 to 38,000 years old. The scientists collected the shells from abandoned Adelie penguin colony sites from three major regions in Antarctica: the Ross Sea, East Antarctica and the Antarctic Peninsula.

Their findings are published in the current Proceedings of the National Academy of Sciences

After crushing bits of the shells with a mortar and pestle, the scientists measured their carbon and nitrogen stable isotopes. The ratios of those basic elements allowed the scientists to determine past and present penguin diets.

"Stable isotopes accurately reflect the diet of living and fossil species because the tissues of the animal absorb the isotope ratios of their prey," Emslie explained to Discovery News.

"Thus you can determine if a species feeds high or low on the food chain based on its isotope composition of its tissues, including eggshell," Emslie, a professor of biology at the University of North Carolina Wilmington, added.

At first, the scientists expected to find that the birds' diets shifted with the ever-changing climate. Instead, they discovered a "dramatic shift in penguin prey high on the food chain, such as fish, over most of the past 35,000 years to prey — krill — lower on the food chain occurring very recently, within the past 200 to 300 years."

At precisely that time, humans began an unprecedented killing of seals and whales in Antarctica. Whale oil was then used to burn lamps, and people also consumed whale meat, a practice continued in some countries. Seals have always been targeted for their pelts, as well as for their meat.

Since whales and seals feast upon krill, their disappearance led to a huge "krill surplus" in the Southern Ocean. It was then that the penguins shifted to this salty, crunchy high-energy prey.

Keith Hobson, a scientist at Environment Canada's Canadian Wildlife Service, told Discovery News that he was "truly surprised at the abrupt change... these results indicate for laying females via their eggs."

However, Hobson pointed out, the shift could have been due not only to a surpluss of krill, but also a scarcity of fish.

He hopes "that this work acts as a catalyst for others to examine the ecological interrelationships occurring in the Southern Ocean.

In the meantime, both he and Emslie are concerned about the current penguin food situation, since krill are in steep decline in the Southern Ocean. Emslie attributes this to "global warming and increased krill fisheries." With many fish species also declining, "Adelie penguins face few foraging options in future," he said.

Emslie hopes implementation of a recent proposal calling for protection of the entire Ross Sea region as an ecological reserve might help to prevent humans from indirectly starving penguins there to death.