Off the northeastern coast of Great Britain, fishing boats are swarmed by seabirds gorging on the undersized catch and fishy waste that is routinely discarded overboard. But as the number of discards are declining—partly due to measures to conserve fish stocks—some predatory birds have turned to eating their feathered fellows with more frequency, according to a new study.

As a consequence of this dietary shift, some defenseless bird communities face a threatening decline in their populations, said Stephen Votier, an ornithologist at the University of Glasgow in the United Kingdom.

Votier is the lead author of a study on how reductions in discarded fish waste are affecting seabird populations. It is being published in tomorrow's issue of the science journal Nature.

The change in the food chain—a result of conservation actions to protect overfished species such as cod—is exacerbated by a decline in sandeel, an alternate fish food for seabirds that is also a staple of fish meal, used in fertilizer and animal food.

For reasons scientists do not fully understand, sandeel populations fluctuate widely and wildly. They are currently at historic lows despite the fact that the North Sea sandeel fishery has been closed since the year 2000. The eel-like fish swim in dense shoals or bury themselves in sandy sediments, and many seabirds catch them to feed their young.

Rather than using the study findings to advocate a return to higher fishing quotas for cod as a means to increase levels of discarded fish for the seabirds, Votier and his colleagues are calling for measures to better understand and conserve sandeels. Ultimately, they would like to see an end to the practice of discarding fish overboard.

"When they do stop discarding, the system will take a jolt, but it should return to a natural equilibrium within a period of time," Votier said. "The most sensible of actions is to actually stop discarding."

Euan Dunn, a marine policy officer with the United Kingdom's Royal Society for the Protection of Birds (RSPB), agrees with the authors' key finding: that great skuas are increasingly preying on other seabirds. Dunn proposes a similar conservation action as the researchers.

"We certainly don't advocate the maintenance of discarding for the benefit of the birds," he said. "But management could embrace the concept of maintaining alternative prey in the form of sandeels, especially as the latter are not caught for human consumption."

Great Skua

At 4.5 pounds (2 kilograms) and 2 feet (61 centimeters) long with a 4.5-foot (137-centimeter) wingspan, the great skua is described by the RSPB as an "aggressive pirate of the seas."

The bird shows little fear of humans, harasses other big predators to steal their meals, and routinely kills and eats small birds such as black-legged kittiwakes, Atlantic puffins, and common guillemots.

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SOURCES AND RELATED WEB SITES Nature The Royal Society for the Protection of Birds