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Fish pulled from the world's lakes and rivers seem to provide a never-ending source of food, jobs and income for people in developing nations.
But there's a hook: As one species is depleted, the next species is targeted. While total catch may remain high, overexploitation of the world's fish supply is rapidly threatening biodiversity and balance of the ecosystem, according to new research in December's issue of BioScience.
"Overfishing of inland waters is a neglected crisis," said Dr. Kirk Winemiller, Texas Agricultural Experiment Station fish researcher.
Winemiller studied the issue of decreasing inland fish numbers with J. David Allan, University of Michigan; Robin Abell, World Wildlife Fund in Washington, D.C.; Zeb Hogan, University of Wisconsin; Carmen Revenga, The Nature Conservancy; Brad Taylor, University of Wyoming; and Robin Welcomme of the Long Barn in Suffolk, England.
The team said it will take local people working with fisheries experts to develop plans to co-manage the "critically harvested" bodies of water.
But netting human actions with ecosystem-based fisheries, management may be long in developing. A major reason is the lack of attention paid to the problem, Winemiller said.
Although many studies have documented overfishing to be a major cause of the decline of global fisheries, most of the focus is on oceans with inland waters rarely mentioned, Winemiller said. Yet, he said, fish from inland waters are more threatened than those in oceans.
Reason for little attention is because not enough information has been gathered, he said, and because many factors overlap and intertwine to threaten these areas.
"Tens of millions of people in developing countries fish inland waters for food and to earn a living," Winemiller said. "Typically, fishing pressure shifts from species to species as preferred types or those more easily captured decline in number.
"So, the overall catch appears stable while biodiversity declines until a point of collapse may be reached," he explained.
The researchers noted that the total catch from inland waters was about 8.7 million metric tons in 2002, the last year for which numbers are available, and that does not include recreational fishing or fishing from aquaculture farms. Most of that – 65 percent – was from Asia, the report indicates. Overall harvest from the world's lakes and rivers has quadrupled since 1950, when data collection first began by the United Nations Food and Agriculture Organization, according to the paper.
Among the critically endangered fish cited in case studies by the team are the Mekong giant catfish of the Mekong River basin in Cambodia and the Murray cod of the Murray River basin in Australia. The lake sturgeon of the Saint Lawrence River and Great Lakes between Canada and the U.S. is noted as currently vulnerable.
Commercial fishing in rivers and lakes is not as intense in North America as it is in many other parts of the work, Winemiller noted.
"Nonetheless, the increase in recreational fishing may be having a huge impact on fish numbers though poundage of harvest is generally not reported," he said.
The Food and Agriculture Organization estimates about 2 million metric tons are gleaned from inland waters in the world every year. Research has demonstrated that reductions of some of these species can profoundly affect productivity and other ecological attributes of freshwater ecosystems, Winemiller added.
"Managing fisheries today is not limited to just satisfying the commercial fishing industry, but must accommodate the wide array of economic and social benefits that people derive from freshwater ecosystems, including food security and economic growth," the team's research noted.
Source: Texas A&M University - Agricultural Communications. December 2005
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