In Mediterranean, the Predator Is the Hunted

"We now understand that both on land and in the sea, large predators play important roles in regulating both the total number and the behavior of their prey," Worm wrote. "Unchecked by their predators, some of these prey species can wreak havoc on ecosystems -- this is one important reason to keep predators around in sufficient numbers."

Another team of researchers, headed by Nicholas K. Dulvy, a biology professor at Simon Fraser University in British Columbia, found that in the open ocean, sharks that used to be an inadvertent bycatch for vessels seeking tuna and swordfish are increasingly being targeted for their meat and fins. The group, which belongs to the World Conservation Union's Shark Specialist Group, surveyed 21 pelagic shark and ray species, and determined that only pelagic stingrays and salmon sharks do not face risk of extinction. Others, such as thresher, ocean whitetip and shortfin mako sharks, are all vulnerable, they wrote.

Sonja Fordham, a co-author of their paper in the journal Aquatic Conservation Marine and Freshwater Ecosystems, said pelagic sharks, which regularly cross vast oceans, face heightened pressures because there are no international catch limits. "Even though these are wide-ranging and fast-moving sharks, they are at risk," Fordham said in a phone interview from Brussels, where she advocates for tighter European shark-fishing regulations as the shark conservation program director for the advocacy group Ocean Conservancy.

Heike K. Lotze, another Dalhousie marine biologist who co-authored the article with Ferretti, wrote in an e-mail that the recent burst of shark research reflects both an increasingly sophisticated use of "unconventional data" and the recognition "that human impacts have strongly altered ocean ecosystems for a long time and thus shifted our perception of what is natural in the oceans."

Bowman said she and other advocates hope fishery managers will "figure out how to control fishing to prevent further declines" of sharks, and policymakers are responding. On June 19, the National Oceanographic and Atmospheric Administration announced it would ban the removal of shark fins at sea in the Atlantic and Gulf of Mexico by late July and cut the permitted catch of sandbar and porbeagle sharks.

A week earlier, the House Natural Resources Committee advanced legislation that would institute the "fins attached" requirement nationwide. International fishery managers will debate this fall the idea of imposing worldwide shark catch limits.

Enric Cortes, a scientist at NOAA's Fisheries Service who conducts shark- population assessments along the East Coast, emphasized that scientists are still learning about the role sharks play in ecosystems. They may dominate more isolated regions, but they don't necessarily shape every marine environment they inhabit: "The jury is still out on that."