Many coastal fisheries are in trouble, yet according to figures reported to the United Nations, the annual worldwide yield has appeared to be stable or even growing. By reported numbers, for example, Chinese fisherman have annually hauled more than 15 million tons of food from the sea for 3 years running, and their bounty grew to that amount–nearly 20 percent of the world’s total–from 2.5 million tons in 1970.
So, what’s the catch? It’s poorer than reported, according to a new study, and waning with each passing year.
Two marine scientists at the University of British Columbia in Vancouver set out to test the validity of data that the United Nations’ Food and Agriculture Organization (FAO) uses to assess fishery health. The organization relies on nations to report their yields and lacks the capacity to audit those numbers.
Reg Watson and Daniel Pauly estimated fish harvests within ocean cells measuring 0.5 of latitude, or nearly 35 miles, north to south and 0.5 of longitude across. They accounted for factors such as each cell’s depth, its surface temperature, and the amount of the sun’s energy that enters the food chain through plant growth there.
Using data from the FAO and other sources, the researchers estimated the catch from 176,000 ocean cells and calculated each factor’s influence on catch. They then designed an equation to model the catch in any given cell.
The statistical model produced reasonable year-by-year estimates for most cells around the world, but the calculated fish yields near China’s shore consistently came up short. In the Nov. 29 Nature, Watson and Pauly estimate that the catch within China’s exclusively managed zone in 1999 was barely half as large as reported. They suspect that China’s economic system generates inflated numbers because officials’ promotions have, in part, depended on reports of increased output.
The researchers substituted their new estimates for China’s existing FAO data to produce revised global-catch figures for the past 3 decades. The new trend shows that global catch has “actually been dropping since 1988,” says Watson.
That finding, he adds, underscores the grave nature of recent collapses in many regional fish stocks, which have increasingly forced fishers to exploit international waters. The data indicate that fish populations in the high seas can’t fully compensate for depleted national stocks. “The system in place for getting global fishery statistics has misled us . . . to believe we had a sustainable and continuous supply from the world’s oceans,” says Watson.
The large “alleged discrepancies” have implications mainly for China’s coastal fisheries, “because China is not an important food-fish exporter,” says Richard Grainger, the chief of the FAO’s fisheries data unit. Science News reached Grainger in China, where he is working with local authorities to improve the quality of the statistics in question.
Jane Lubchenco of Oregon State University in Corvallis construes the problem as larger. Because China’s catch is so large, inaccurate reporting “has totally distorted the picture” and created the false impression of a stable world catch. The disillusioning new data indicate that “we are seriously overfishing the ocean on a global scale,” she says. She credits Watson and Pauly with using innovative methods to generate data previously unavailable.
The study sounds “a call for urgency,” says Andrew A. Rosenberg of the University of New Hampshire in Durham. Governments must act to stop overfishing before it further imperils world food supplies, he says.