Overfishing Large Sharks Impacts Entire Marine Ecosystem

Ransom's Myers last paper before his death this week reports that fewer big sharks in the oceans also means bay scallops are harder to find at market. Ecologists and scientists have thought for a long time that the effects of removing the ocean's top predators, big sharks, would cascade through the food web. This is the first study to demonstrate that cause and effect—a holy grail of conservation biology.

A team of Canadian and American ecologists, led by Myers and Julia Baum, found that overfishing the largest predatory sharks (such as bull, hammerhead, dusky, and great white sharks) along the Atlantic Coast led to an explosion of ray, skate, and small shark prey species, according to a Dalhousie University press release. Myers held the Killam Chair in Ocean Studies at Dalhousie. The paper appears in this week's Science.

"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 Julia Baum, a co-author of the article. "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. The extent of the declines shouldn't be a surprise, considering how heavily large sharks have been fished in recent decades to meet the growing worldwide demand for shark fins and meat.

"Our study provides evidence that the loss of great sharks triggers changes that cascade throughout coastal food webs," says Baum. "Solutions include enhancing protection of great sharks by substantially reducing fishing pressure on all of these species and enforcing bans on shark finning both in national waters and on the high seas."