luni, 15 septembrie 2008

North American Fish Under Threat

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- Nearly 40 percent of fish species in North America are imperiled, according to a new survey by fish experts, the U. S. Geological Survey, and the American Fisheries Society, up 92 percent from the last survey done in 1989.

North America hosts perhaps the greatest diversity of temperate freshwater organisms on Earth, including aquatic insects, mussels, crayfish and fish.

The new report, compiling assessments from fish experts in the United States, Canada and Mexico, found that of the 700 types of fish in the survey, 230 are "vulnerable," 190 are "threatened," 280 are "endangered," and 61 are believed extinct.

"A lot of effort has been expended since 1989, but things are still in a sorry state in many ways," said study author Eric Taylor of the University of British Columbia in Vancouver. "We can't be complacent with trying to address some of these declines."

No single cause explains the ongoing fish losses, Taylor and others agree. Habitat loss, invasive species, diseases, dams, and water contaminants all contribute.

"Fish are kind of canaries in the coal mine," said Howard Jelks of the USGS and lead author of the report, published in Fisheries. "If you change the water to something that's not able to support these fish, it's also not going to be as high quality for recreating, for eating the fish out of these streams, for drawing water that's ultimately used for drinking, or for other things."

Certain regions were identified as hotspots with both high fish diversity and high degrees of threat. These included the Pacific central valley, the western Great Basin, the Rio Grande, and several river systems in the southeast such as the Tennessee and Mobile.

Pacific Coast salmon and trout were among the most at-risk types of fish, as were minnows, suckers, and catfish across the continent. Almost half of the carp and minnow family and the family of fish including perch and darters were identified in one of the imperiled categories.

The new report lists distinct sub-populations of certain fish separately, even if they are classified as the same species, which accounts for part of the increase.

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