海角大神

A report that scientists are calling one of the most comprehensive studies of great white sharks finds their numbers are surging in the ocean off the Eastern U.S. and Canada after decades of decline.

The study by National Oceanic and Atmospheric Administration scientists, published this month in the journal PLOS ONE, says the population of the notoriously elusive fish has climbed since about 2000 in the western North Atlantic.

The scientists behind the study attribute the resurgence to conservation efforts, such as a federal 1997 act that prevented hunting of聽great聽whites, and greater availability of prey. The species is listed as vulnerable by the International Union for Conservation of Nature.

"The species appears to be recovering," said Cami McCandless, one of the authors. "This tells us the management tools appear to be working."

Great聽whites聽owe much of their fearsome reputation to the movie "Jaws," which was released 39 years ago Friday. But confrontations are rare, with only 106 unprovoked聽white聽shark聽attacks 鈥� 13 of them fatal 鈥� in U.S. waters since 1916, according to data provided by the University of Florida.

They are, though, ecologically critical. They are apex predators 鈥� those at the top of the food chain 鈥� and help control the populations of other species. That would include the gray seal, whose growing colonies off Massachusetts have provided food.

"You should be concerned for a good reason," said James Sulikowski, a professor of marine science at the University of New England in Portland, who was not involved in the study but noted it could help better target future conservation efforts for聽great聽whites. "We need these聽sharks聽in our waters."

A separate study published in PLOS ONE this month suggested that聽great聽whites鈥� also known just as聽white聽sharks聽鈥� are also returning to abundance in the eastern north Pacific Ocean.

"There's this general pattern of where the聽white聽sharks聽are protected, they seem to recover," said Tobey H. Curtis, one of the authors of the Atlantic study.

The elusive nature of聽white聽sharks聽and the lack of historical data about their population levels required the authors to rely on sightings of聽sharks, as opposed to other ways to count sea life, such as commercial fishing surveys and census counts, Curtis said.

The research adds recent unpublished data to previously published records to establish 649 confirmed聽white聽shark聽sightings from 1800 to 2010. The data show that a period of decline in聽white聽shark聽abundance during the 1970s and 1980s has reversed, the authors said.

White聽shark聽abundance in the western North Atlantic declined by an estimated 73 percent from the early 1960s to the 1980s, the report says.聽Shark聽abundance is now only 31 percent down from its historical high estimate in 1961, the report states. The report does not provide a local estimate for the聽great聽white聽sharkpopulation, which some scientists say is between 3,000 and 5,000 animals.

The report also illuminates where people encounter聽white聽sharks聽鈥� mostly between Massachusetts and New Jersey during the summer and off Florida in the winter, it says.

They also migrate based on water temperature and availability of prey, and are more common along the coast than offshore, the report states.

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