In today’s issue of Science, there is a study showing that hunting of sharks, by eliminating the main predator of rays, leads to a decline in the ray’s – and ours – food: the scallops:
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.
Here is a local North Carolina angle:
Too many sharks have been killed, so they’re no longer devouring a voracious predator that feasts on bay scallops, marine researcher Charles “Pete” Peterson concludes. As a result, North Carolina’s bay scallops fishery, once worth $1 million a year, has been wiped out.
The finding, reported today in the journal Science, is evidence that harm to one creature in an ecosystem can unexpectedly injure another, Peterson said.
“The marine environment is so vast and three dimensional, there are many linkages,” he said. “There are cascading and domino effects.”
Sharks don’t eat scallops. But the top predators do feast on cownose rays — kite-shaped creatures that migrate through North Carolina waters. And the rays eat scallops, hordes of them, as they make their late-summer and early-fall travels south.
The timing of the cownose trip past North Carolina is particularly harmful to scallops, Peterson said. The rays arrive from from mid-August to mid-September. Scallops, which live about 18 months, don’t start spawning until September. So the rays eat them before they can reproduce.