Why Are These Predators Vulnerable to Overfishing?

Unlike fish species lower on the food chain, which spawn millions of eggs, shark reproductive strategy produces few adults. Shark young, though relatively large at birth, are few in number; the average is 3-12 pups per litter. Since they are cold-blooded, the rate at which the embryo develops depends on water temperature; females can be pregnant for as long as 22 months. Juvenile sharks grow slowly, taking an average of 12 to 25 years--and up to as long as 30 years--to reach sexual maturity. This means that once a shark population has been depleted, it takes decades to replenish itself.

Shark harvesting increased dramatically during the 1980s and early ‘90s, as huge fishing operations grew ever more efficient and as other fish populations dropped. By 1987 fishermen were killing more large coastal sharks than were being born. “At the current rate,” predicted marine biologist Dr. Merry Camhi of the National Audubon Society’s Living Oceans Program in 1997, “some species will reach ecological extinction within ten years.” We are only beginning to learn how these ancient creatures live and how their unique physiology could help humans.