If fishing around the world continues at its present pace, more and more species will vanish, marine ecosystems will unravel and there will be a "global collapse" of all species currently fished, possibly as soon as mid-century, fisheries experts and ecologists are predicting.

The scientists, who are to report their findings today in the journal Science, say it is not too late to turn the situation around. As long as marine ecosystems are still biologically diverse, they can recover quickly once overfishing and other threats are reduced, the researchers say.

But they add that there must be quick, large-scale action to protect remaining diversity, including establishment of marine reserves and "no take" zones, along with restrictions on particularly destructive fishing practices.

The researchers drew their conclusion after analyzing dozens of studies and fishing data collected by the U.N. Food and Agricultural Organization and other sources. They acknowledge that much of what they are reporting amounts to correlation, rather than proven cause and effect.

And the data from the Fishing and Agricultural Organization have come under criticism from researchers who doubt the reliability of some nations' reporting practices, said Boris Worm, a fisheries expert at Dalhousie University in Nova Scotia, who led the work.

Still, he said in an interview, "there is not a piece of evidence" that contradicts the dire conclusions.

Jane Lubchenco, a fisheries expert at Oregon State University who had no connection with the work, called the report "compelling."

"It's a meta analysis, and there are challenges in interpreting those," she said in an interview, referring to the technique of analyzing a host of previous studies. "But when you get the same patterns over and over and over, that tells you something."

Twelve scientists from the United States, Canada, Sweden and Panama contributed to the work.

"We extracted all data on fish and invertebrate catches from 1950 to 2003 within all 64 large marine ecosystems worldwide," they wrote. "Collectively, these areas produced 83 percent of global fisheries yields over the past 50 years."

In an interview, Worm said, "We looked at absolutely everything — all the fish, shellfish, invertebrates, everything that people consume that comes from the ocean, all of it, globally."

The researchers found that 29 percent of species had already been fished so heavily or were so affected by pollution or habitat loss that they were down to 10 percent of previous levels, a situation the scientists called collapse.

This loss of biodiversity seems to restrict the ability of marine ecosystems as a whole to recover from overfishing, Worm said. That results in an acceleration of environmental decay and further loss of fish, with potentially serious consequences to people and economies dependent on them.

Worm said he analyzed the data for the first time on his laptop while he was overseeing a roomful of students taking an exam. What he saw, he said, was "just a smooth line going down." And when he extrapolated the data into the future "to see where it ends at 100 percent collapse, you arrive at 2048."

"The hair stood up on the back of my neck and I said, 'This cannot be true,"' he recalled. So he ran the data through his computer again. And then he did calculations by hand. The results were the same.

"I don't have a crystal ball and I don't know what the future will bring, but this is a clear trend," he said. "There is an end in sight, and it is within our lifetimes."