LiveScience.com - Alarming Decline of Sharks Causing Other Species to Vanish: "The precipitous decline in large predator sharks in the Atlantic Ocean in the past decade has made ecologists worry about a trickle-down effect on the ocean ecosystem.
A new study supports the case. With the large predators gone, their prey—smaller sharks and rays—are free to feast on lower organisms like scallops and clams, depleting valuable commercial stocks.
“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,” said study team member Julia Baum of Dalhousie University in Halifax, Nova Scotia.
Shark populations all over the world have plummeted because of intentional fishing for their fins, which are eaten and used for medicines in Asia
For this study, published in the March 30 issue of the journal Science, the researchers looked at surveys of populations of 11 great shark species, conducted between 1970 and 2005. Every species had substantially declined in just those few decades. The smallest observed decline was in sandbar shark populations, which had decreased nonetheless by 87 percent. Other species, including the bull, dusky and smooth hammerhead sharks, may have declined by more than 99 percent.
“They’re all down dramatically,” said study co-leader Charles Peterson of the University of North Carolina."