Hammerhead and white shark populations along the East Coast of the United States have declined to less than a quarter of their former size in the last 15 years while most other known shark species have declined by at least 50% in that time, according to a survey of Northwest Atlantic shark populations published in Friday's issue of Science.
The animals are victims of overfishing for their fins and flesh and accidental harvesting by long-line fishing fleets that target tuna and swordfish, said the report's lead author, Julia K. Baum of Dalhousie University in Halifax, Canada.
Baum said the magnitude of the declines, coupled with sharks' slow rate of reproduction, means that several species are at risk of extinction. Because sharks occupy a high place in the marine food chain, the scientists warn that changes in shark populations will likely ripple through marine ecosystems. "Pervasive overfishing of these species may initiate major ecological changes," according to the report.
The biologists suggest reducing shark-fishing and designing marine reserves to safeguard sharks and other marine animals that are in decline.