A study published last week in the journal Science predicts the world's fishing areas may be exhausted by 2048 because of overfishing and pollution.

"The problem is not overfishing," said Vito Calomo, executive director of the Massachusetts Fisheries Recovery Commission. "You have to have management rules because there are species that need help, but the major problem is pollution, global warming, (and) destruction of the habitat."

The study, conducted over four years by a group led by Boris Worm of Canada's Dalhousie University, concluded that without changes in fishing rates, the world's oceans could become bereft of usable stocks.

"If the long-term trend continues, all fish and seafood species are projected to collapse within my lifetime - by 2048," Worm wrote. "It is a very clear trend."

A seafood species is determined to have collapsed when the catch falls below 10 percent of the maximum annual haul. By 2003, 29 percent of seafood species were in that category, the scientists said.

Calomo bristled at the suggestion that the fishing industry is to blame for changed ecosystems, saying that the local industry is too weak at this time to lead to a collapse. But he did point to large industrial trawlers and vessels in other parts of the world, particularly the European Union, Russia and China, that fish around the clock without the stringent controls on catch and days at sea American fishermen must follow.

"If you're going to fish 24-7 like they do out there, then I could see it happening," Calomo said. "We have the technology to catch the last living fish today."

However, chemicals dumped in the ocean by the United States and other countries, along with runoff and chlorine from water treatment facilities, do more to disrupt the oceans' ecosystems than overfishing.

"We've been fishing for 400 years, but the fish have always come back," Calomo said.

He pointed to the Chesapeake Bay, where a decline in the amount of sturgeon, oysters and crab was blamed on overfishing. After studying the bay, the National Marine Fishery Service found that pollution in the bay had changed the ecosystem. Many of those species are rebounding now, Calomo said.

The decline in fishing ground stocks can be stopped by the establishment of protected marine reserves, the scientists found after studying 44 such areas. Closing the fisheries and creating reserves led to a 23 percent average increase in species diversity, they said. At the same time, fishing around the reserves became four times more productive. "We can turn this around," Worm said. "We won't see complete recovery in one year, but in many cases species come back more quickly than people anticipated - in three to five to 10 years. And where this has been done we see immediate economic benefits."

Aside from seafood, the "services" provided by marine creatures include the filtration and detoxification of ocean water and processing carbon dioxide into food and oxygen. Coastal habitats such as mangroves and marshland also provide a defense against flooding.

The scientists conducted experiments, examined coastal areas and analyzed data from the world's main ocean fishing sites to gauge the effect of species diversity on survival.

Bloomberg News service contributed to this report.