Wild fish catch hits limit.

• Author: Larsen, Janet
• Position: EYE ON ECOLOGY

AFTER DECADES OF GROWTH, the reported global wild fish catch peaked in 2000 at 96,000,000 tons, then fell to 90,000,000 tons by 2003, the last year for which worldwide data are available. The catch per person dropped from an average of 17 kilograms in the late 1980s to 14 kilograms in 2003--the lowest figure since 1965.

As fishing fleets expanded through the late 1980s and fish-finding and harvesting technologies became more efficient, the world's fishers systematically have gone after their catch at greater depths and in more remote waters. Over the past 50 years, the number of large predatory fish in the oceans has dropped by a startling 90%. Catches of many popular food fish such as cod, tuna, flounder, and hake have been cut in half despite a tripling in fishing effort. According to the United Nations Food and Agriculture Organization, the 4,000,000 vessels scouring the world's waters are at, or exceeding, the sustainable yields of three-quarters of all oceanic fisheries.

The 10 most-fished species constitute 30% of the world's catch. Seven of these have reached their limits and are classified as fully exploited or overexploited throughout their entire ranges, meaning that we cannot expect to increase their harvests. Included in this group are two types of Peruvian anchoveta, Alaska pollock, Japanese anchovy, blue whiting in the northeast Atlantic, capelin in the North Atlantic, and Atlantic herring. The other three species--chub mackerel, skipjack tuna, and largehead hairtail--are overfished in parts of their ranges.

Interestingly, several of these species became fishing targets only after the stocks of more desirable fish were overharvested. After the collapse of the 500-year-old Canadian cod fishery in the early 1990s, blue whiting catches increased. In the northwest Pacific, the overfishing of Alaska pollock and Japanese sardine led fishers to focus on Japanese anchovy, largehead hairtail, and squid. Some scientists warn that continuing to "fish down the food web" will lead to harvests almost exclusively of bait fish and jellyfish.

The tendency to catch larger and older fish first, leaving those small enough to escape from nets to breed, has, over time, reduced the average size of those caught. The effect on large predators is striking. In the 1950s, for instance, an average blue shark weighed 52 kilograms; in the 1990s, 22 kilograms. In addition, fish that breed late in life sometimes are pulled out of the water before they can...