Sharks are in trouble, with their populations in serious decline around the world in large part because of overfishing, according to marine scientists gathered at a conference in California. More than 100 million sharks are caught each year by crews from 125 nations, and only four of those — Australia, Canada, New Zealand, and the U.S. — have implemented management plans for shark fisheries. Shark fins are increasingly sought as a delicacy. Off the Hawaiian islands, finning — the practice of cutting off a shark’s fin and tossing the rest of its carcass back in the ocean — increased 2,000 percent between 1991 and 1998, according to the Ocean Wildlife Campaign. Reps. Randy Cunningham (R-Calif.) and Jim Saxton (R-N.J.) last month introduced a bill that would permanently ban shark finning in all U.S. waters and direct the Secretary of State to work toward a similar ban worldwide.