Glen Martin, Chronicle Environment Writer
The world's fisheries are tanking, going the way of the dodo and the passenger pigeon. The causes are many, but the primary one, say marine scientists, is humankind's insatiable appetite for seafood.
A recent report to the Pew Oceans Commission determined that between 25 and 30 percent of the world's fish populations are overfished, while an additional 40 percent are "fully exploited" -- meaning that additional pressure could result in their collapse.
Pollution and oceanic temperature fluctuations have played a role in reducing some fisheries, but scientists increasingly concur that overfishing on a vast scale is the primary culprit.
The issue will be explored in detail in the documentary "Empty Oceans, Empty Nets," which will be broadcast in the Bay Area on KQED-TV, Channel 9, next Monday at 9 p.m. It also will run on other public broadcasting stations across the country.
Paul Dayton, a professor of oceanography at the Scripps Institution of Oceanography in La Jolla (San Diego County) and a co-author of the Pew report, said little is being done to address the crisis.
"Everyone agrees it's a desperate situation, but the tendency is to complain rather than bite the bullet and do something substantive about it," he said. "The sea is a commons, and everyone is looking out for their own self-interest. In the simplest terms, the fight is over who will catch the last fish rather than husbanding and restoring the fisheries."
There are some modest exceptions to the trend: Wild salmon and halibut are doing well in Alaska, and the California sardine fishery -- which collapsed more than 50 years ago -- has shown partial recovery.
But the overall situation is bleak, with too many people chasing after a declining number of fish.
During the past 20 years, the size of the global fishing fleet has expanded dramatically, stimulated in large part by government aid programs. Estimates for the commercial fleet range upward of 3.5 million to 4 million boats.
These craft range from 150-foot-long high-seas "factory" trawlers that net thousands of tons of fish, process them on board and dock with flash-frozen packages of fish sticks in the hold to "artisanal" boats fitted with outboards that ply coastal waters in the developing world.
All exert a pressure on the world's fisheries that is unrelenting.
"Approximately 50 percent of the global continental shelf is now trawled, with the most productive areas trawled several times a year," Dayton said. "There is no area in the world that is not feeling heavy impacts."
Trawling involves dragging large nets across the ocean floor. It was identified in a recent report by the National Research Council as a particularly harmful fishing mode because trawl nets destroy coral and rocky reefs and take huge amounts of "by catch" -- noncommercial species that include everything from shellfish to sponges to sea turtles.
"Trawling is like bulldozing a forest to catch songbirds," said Sylvia Earl,
an oceanographer, deep diving record holder and explorer-in-residence for the National Geographic Society.
"The destruction to the marine environment is horrendous, and it's exacerbated by the fact that many governments --including our own -- overcapitalized the industry," Earl said. "You have a tremendous number of boats built by low-interest loans competing after fewer and fewer fish."
Trawlers aren't the only problem, say scientists. Long-liners -- boats that spool out miles of lines fitted with thousands of baited hooks in a single set -- are wiping out swordfish and other billfish in tropical and semitropical seas worldwide.
NETS, DYNAMITE AND CYANIDE
Coastal and high-seas drift nets account for huge catches of large fish and are also responsible for "ghost nets" --broken-off sections of net that drift in the ocean for months or years, entangling and killing dolphins, sea birds, sea turtles and sharks.
The problem isn't restricted to the open ocean. Coral reefs, the essential habitat for a huge assemblage of fish and invertebrates, have been laid waste throughout southeast Asia.
"A couple of decades ago, Indonesia was a coral Eden," said John McCosker, chairman for aquatic biology at the California Academy of Sciences in San Francisco. "Today, it has been utterly destroyed by fishermen using dynamite and cyanide, except for a few reserves and resorts where you literally have armed guards patrolling the reefs."
In the tropical Pacific, dynamite is increasingly used to collect marketable fish, obliterating young fish, coral and bottom-dwelling invertebrates in the process. Cyanide is used to stun small fish for the aquaria trade, a process that also destroys coral reefs.
AFTERMATH OF AQUACULTURE
Another significant problem, McCosker said, is the global boom in aquaculture -- the artificial propagation of fish and shellfish.
In the tropics, McCosker said, huge shrimp farms are displacing mangrove wetlands, vital nursery areas for myriad marine species. And in the temperate northern and southern latitudes, salmon farms are contaminating estuaries with waste and drugs used to fight fish diseases.
"In British Columbia, pen-raised salmon are also escaping to the wild, endangering native runs," McCosker said. "In terms of the marine environment, aquaculture is one of the biggest threats going. We don't serve shrimp or farmed salmon at academy functions anymore."
Traditional fishery management approaches are proving inadequate in addressing the problem. In fact, scientists say, they are a big part of the problem.
Current management practices are based on the idea that you target the big fish, notes Paul Dayton of the Scripps Institution. But the big fish are the very ones you need to propagate the species because they are sexually mature.
Fisheries management also encourages fishing on spawning populations -- large masses of fish that have gotten together to propagate. "That's happening all over the world and (in U.S. waters) it's happening on cod, haddock, pollack, sheephead and squid," Dayton said. "It's a surefire recipe for destroying a fishery."
What to do? Most marine biologists recommend reducing the global fishing fleet through government buyouts of fishing permits and boats. Last month, the National Marine Fisheries Service spent $10 million buying groundfish permits from New England fisherman, and a similar idea has been discussed for the West Coast.
Educating consumers about "eco-friendly" and unfriendly fisheries -- as the Monterey Bay Aquarium does with a handy wallet card -- is another option.
And an important step for intercoastal and reef species, Dayton said, is to establish rigorously protected marine reserves. Current refuges -- including those in the United States -- have inadequate protective safeguards, he said.
"Fish are wildlife, not domestic animals, and they need places to feed, reproduce and rest, just like terrestrial wildlife," Dayton said. "We have solid data that demonstrates refuges benefit both the fisheries and fishermen, because large fish continually migrate outward from the protected zones."
The depletion of the world's marine fisheries is of such scope that many scientists are, in their own words, feeling depressed.
"It gets to me," conceded McCosker. "I'm amazed by how little people know about it. But I'm also amazed by how concerned they are once they start learning. Once you tap into the public consciousness, you find a tremendous commitment to changing things."
E-mail Glen Martin at email@example.com.