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Seabird Bones Reveal Changes in Open-Ocean Food Chain

The bones of generations of seabirds reveal that a dramatic shift has occurred in the ocean's food web.

Hawaiian petrels spend most of their lives foraging the open waters of the Pacific Ocean, from the equator to Alaska's Aleutian Islands. But they nest in caves and burrows, where, if they die, their bones are preserved.

Scientists from Michigan State University and the Smithsonian Institution measured a collection of more than 17,000 petrel remains for the ratio of nitrogen isotopes, unique molecules that reveal what -- and where on the food chain -- the birds were eating.

They found that between 100 and 4,000 years ago, petrels fed on large prey such as squid and crustaceans. But as industrial fishing operations began moving beyond the continental shelf in the mid-20th century, the birds were forced to subsist on a diet of smaller fish and other prey.

Writing in The Proceedings of the National Academy of Sciences, co-author Peggy Ostrom says the team's study is one of the first to explore "whether fishing has gone beyond an influence on targeted species to affect nontarget species and potentially, entire food webs in the open ocean."

The Hawaiian petrel is an endangered species. A similar shift in diet for another coastal seabird was associated with decreases in its population.