Experts report downward spiral of marine species, but they say quick action could reverse slide

The world's oceans are under an increasing assault from over-fishing, pollution and global warming that threatens to wipe out vital fisheries and to create a crisis in food supplies before the middle of this century, an international team of scientists warns.

There is still time to reverse the trend, the researchers say, but only if quick action protects depleted fisheries more effectively and saves ocean habitats by creating new marine reserves.

The biologists and economists worked together for four years and reached their conclusions after poring over data detailing every conceivable threat to marine biodiversity and the effectiveness of efforts to reverse the downward trend. Their report is published today in the journal Science.

Much of their data is not new, they said, but the report is the first to analyze all the cumulative research on threats to the marine ecology and particularly to ocean species -- from microscopic plankton at the base of the marine food web to the small fish that feed larger fish to the vital fisheries that feed billions of the world's human population.

"Whether we looked at tide pools or studies over the entire world's oceans, we saw the same picture emerging," said Boris Worm, a marine biologist at Dalhousie University in Nova Scotia and the team leader. "In losing species, we lose the productivity and stability of entire ecosystems.

"I was shocked and disturbed by how consistent these trends are -- beyond anything we suspected. If the long-term trend continues, all fish and seafood species are projected to collapse within my lifetime -- by 2048," said the 37-year-old scientist.

Jane Lubchenco, a leading marine biologist at Oregon State University who was not involved in the study, called the report "a really focused analysis and a compelling message of urgency and hope."

"It shows conclusively how ocean ecosystems are being seriously disrupted but that the downward spiral can be reversed," said Lubchenco, a former president of the American Association for the Advancement of Science.

Already, the researchers found, about 90 percent of all the fish and seafood species in the world's oceans have been depleted within the past century, meaning that the annual catch of them has been cut at least in half. Of those species, 38 percent have collapsed, meaning that their populations have plunged by more than 90 percent -- a road to possible extinction without intensified efforts to protect them, the researchers said. Seven percent of the fish in their study already have become extinct, they said.

But many of the threatened species can recover, said Worm, noting that in the group's study of 48 areas around the world where marine biodiversity has been effectively protected, fish and seafood stocks have rebounded and increased fourfold within a very few years.

"Less than 1 percent of the global ocean is effectively protected right now," said Worm. "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."

Stephen Palumbi of Stanford University's Hopkins Marine Station in Monterey, a co-author of the Science paper, agreed that the situation is dire but not hopeless as long as concerted conservation efforts are enacted.

"Unless we fundamentally change the way we manage all the oceans species together, as working ecosystems, then this century is the last century of wild seafood," Palumbi said.

He pointed to some changes that already are paying off. Rockfish off the California coast, for example, once were in serious decline because of overfishing, but stringent state laws regulating catches reversed that problem, and the species is rebounding, he said.

He and Worms also noted that marine reserves along the California coast created by state law, and federally protected areas like the Monterey Bay National Marine Sanctuary, also have helped reverse the downward trend in fish resources there.

So have carefully planned aquaculture projects that take the pressure off commercial fisheries, Palumbi said. But he noted that although carp are farmed in China with only plant material as their feed, in many cases fish-farming means feeding the farmed species like salmon with processed smaller wild fish -- and that can mean a self-defeating and ecologically disrupting use of resources, he said.

"It's like turning on your air-conditioner and using electricity instead of opening your window," he said.

The huge study, financed by the National Science Foundation, analyzed global catch data collected by the U.N. Food and Agricultural Organization; it also collected records from a dozen coastal regions in Europe, Australia and the United States, including San Francisco Bay, and tallied detailed records of fish losses in 64 large marine ecosystems around the world.

90% of the world's fish and seafood have been depleted in the past century.

38% of the depleted species have declined by more than 90 percent.

7% of the species of fish studied by researchers have become extinct.

• San Francisco Chronicle