Informant38

Shark populations in the northwest Atlantic have plunged by more than half since scientists began closely tracking them in 1986, with marquee species like the hammerhead and the great white falling more than 75 percent, researchers say.
Such an abrupt decline in the ocean's dominant hunters is likely to alter marine food chains in ways that are impossible to predict and that might take decades to reverse, the researchers and other experts said.
The researchers, from Dalhousie University in Halifax, Nova Scotia, ascribed the drop to intensifying commercial and recreational fishing for sharks, which reproduce slowly compared with other oceanic fish. They describe their findings in Friday issue of the journal Science.
The Dalhousie researchers said similar drops had probably occurred elsewhere and said "pervasive overfishing of these species may initiate major ecological changes."

They said there was no evidence that the drop was due to any natural cycle, partly because similar trends have been recognized in the Pacific and other waters with heavy fishing pressure.