Scallop decline blamed on shark fishing

With fewer sharks to devour them, skates and rays have increased sharply along the East Coast and they are gobbling up shellfish, particularly bay scallops, researchers report in today's issue of the journal Science.

Ecologists have known that reducing key species on land can affect an entire ecosystem, but this study provides hard data for the same thing in the ocean, said lead author Charles H. Peterson of the Institute of Marine Sciences at the University of North Carolina.

Co-author Ransom A. Myers of Dalhousie University in Halifax, Nova Scotia, and Peterson were studying different ends of the food chain, Peterson said in a telephone interview.

"Myers was working on great sharks and I was working on cownose rays and their impact on bay scallops and other shellfish. We realized that separately we had interesting science, but together we had an absolute revelation," he said.

"We were able to show why these top predators matter . . . that there was a consequence," Peterson said.

Peterson, who works at the university center in Morehead City, N.C., said scallops used to be so abundant there that people were allowed to collect a bushel a day. "The kids were able to see that food doesn't just come from a market," he said.

Now, scallops are very reduced, he said. "The rays, as they come through, eat all that are in any dense patch and have eaten so many there does not appear to be enough to create spawning stock."

Scallops are an easy target because they do not burrow into the sand, Peterson said. Millions of rays from Chesapeake Bay migrate through the area, he said. "What are they going to feed on to fuel their migration?"

In some areas they enter seagrass beds and dig up clams, but that is an important nursery habitat for shrimp, blue crabs and fish, Peterson said, "so there is a high concern that we may now be cascading to habitat destruction."

Steve Murawski, director of scientific programs at the National Marine Fisheries Service, was not so sure. He said the links between the large sharks, medium-size rays and bay scallops were "tenuous."

There is very little food and feeding data on the rays, he said, and habitat degradation and environmental issues also could be factors in the bay scallops' decline. As for the increase in rays, he said, they used to be widely caught and discarded and fishing has declined in their prime habitat.