By Cornelia Dean
    The New York Times

    Thursday 02 November 2006

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

    The scientists, who 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 improvements must come quickly, said Boris Worm of Dalhousie University in Nova Scotia, who led the work. Otherwise, he said, "we are seeing the bottom of the barrel."

    "When humans get into trouble they are quick to change their ways," he continued. "We still have rhinos and tigers and elephants because we saw a clear trend that was going down and we changed it. We have to do the same in the oceans."

    The report is one of many in recent years to identify severe environmental degradation in the world's oceans and to predict catastrophic loss of fish species. But experts said it was unusual in its vision of widespread fishery collapse so close at hand.

    The researchers drew their conclusion after analyzing dozens of studies, along with fishing data collected by the United Nations 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 F.A.O. data have come under criticism from researchers who doubt the reliability of some nations' reporting practices, Dr. Worm said.

    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 collective analysis of disparate studies. "But when you get the same patterns over and over and over, that tells you something."

    But Steve Murawski, chief scientist of the Fisheries Service of the National Oceanographic and Atmospheric Administration, said the researchers' prediction of a major global collapse "doesn't gibe with trends that we see, especially in the United States."

    He said the Fisheries Service considered about 20 percent of the stocks it monitors to be overfished. "But 80 percent are not, and that trend has not changed substantially," he said, adding that if anything, the fish situation in American waters was improving. But he conceded that the same cannot necessarily be said for stocks elsewhere, particularly in the developing world.

    Mr. Murawski said the Bush administration was seeking to encourage international fishery groups to consider adopting measures that have been effective in American waters.

    Twelve scientists from the United States, Canada, Sweden and Panama contributed to the work reported in Science today.

    "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, Dr. 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 been fished so heavily or were so affected by pollution or habitat loss that they were down to 10 percent of previous levels, their definition of "collapse."

    This loss of biodiversity seems to leave marine ecosystems as a whole more vulnerable to overfishing and less able to recover from its effects, Dr. Worm said. It results in an acceleration of environmental decay, and further loss of fish.

    Dr. 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. He said he ran the data through his computer again, then did the 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."

    Dr. Worm said a number of steps could help turn things around.

    Even something as simple as reducing the number of unwanted fish caught in nets set for other species would help, he said. Marine reserves would also help, he said, as would "doing away with horrendous overfishing where everyone agrees it's a bad thing; or if we banned destructive fishing in the most sensitive habitats."

    Josh Reichert, who directs the environmental division of the Pew Charitable Trusts, called the report "a kind of warning bell" for people and economies that depend on fish.

    But predicting a global fisheries collapse by 2048 "assumes we do nothing to fix this," he said, "and shame on us if that were to be the case."