( Fewer big sharks in the oceans mean tha...)Overfishing large sharks impacts entire marine ecosystem, shrinks shellfish supply

A team of Canadian and American ecologists, led by world-renowned fisheries biologist Ransom Myers at Dalhousie University, has found that overfishing the largest predatory sharks, such as the bull, great white, dusky, and hammerhead sharks, along the Atlantic Coast of the United States has led to an explosion of their ray, skate, and small shark prey species.

"With fewer sharks around, the species they prey upon ?like cownose rays ?have increased in numbers, and in turn, hordes of cownose rays dining on bay scallops, have wiped the scallops out," says co-author Julia Baum of Dalhousie.

"This ecological event is having a large impact on local communities that depend so much on healthy fisheries," says Charles Peterson, a professor of marine sciences biology and ecology at the Institute of Marine Sciences, University of North Carolina at Chapel Hill and co-leader of the study.

The research builds upon an earlier study by Myers and Baum, published in Science in 2003, which used data from commercial fisheries to show rapid declines in the great sharks of the northwest Atlantic since the mid-1980s. Now, by examining a dozen different research surveys from 1970-2005 along the eastern U.S. coast, the research team has found that their original study underestimated the extent of the declines: scalloped hammerhead and tiger sharks may have declined by more than 97 percent; bull, dusky, and smooth hammerhead sharks by more than 99 percent.

"Large sharks have been functionally eliminated from the east coast of the U.S., meaning that they can no longer perform their ecosystem role as top predators," says Baum. "The extent of the declines shouldn't be a surprise considering how heavily larg
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Source:University of Miami Rosenstiel School of Marine & Atmospheric Science