9.9.2008 3:34 PM

40% of Freshwater Fish Imperiled

Federal Scientists: Rate of Decline Is "Staggering"

American shad

Photo: NOAA

By Dan Shapley

In a report that would seem more likely coming from an environmental group than the Bush Administration, the U.S. Geological Survey has reported a "staggering" 92% increase in just 20 years in the number of North American freshwater fish considered imperiled.

Now nearly 40% of all freshwater fish species in North America are "in jeopardy" -- 700 species that are either vulnerable, threatened or endangered. And that doesn't even consider the 61 fishes that have already gone extinct.

The report resulted from a collaboration among scientists in the U.S., Canada and Mexico. It includes assessments of both freshwater fish -- those that live in lakes, streams and rivers -- and diadromous fishes that migrate from the ocean to spawn in estuaries and freshwater rivers.

The declines aren't restricted to fish (crayfishes, snails and mussels are showing similar signs of stress), and the list of threats is familiar:

"Freshwater fish have continued to decline since the late 1970s, with the primary causes being habitat loss, dwindling range and introduction of non-native species," said Mark Myers, director of the USGS. "In addition, climate change may further affect these fish."

The USGS press release did not mention the threats, but overfishing is also a problem for some fish, particularly diadromous fish like American shad and Atlantic sturgeon. Habitat loss can come in many forms, including dams -- both active hydropower projects and derelict dams with no modern use -- and development that destroys stream-bank habitat or wetlands. Power plants that use water to cool condensers may also play a role in declines of some species.

Further, suburban sprawl has been eroding gains made since the Clean Water Act. In New York, for instance, even while the most polluted streams have become cleaner since the 1972 act that banned open pollution of the nation's waters, the most pristine streams have become more polluted. That's because increased runoff from pavement -- of oils, salts and silt -- and the clear-cutting of riparian forests have contributed to the degradation of once-untouched watersheds.

According to the USGS: "Nearly half of the carp and minnow family and the Percidae (family of darters, perches and their relatives) are in jeopardy. Fish families important for sport or commercial fisheries also had many populations at risk. More than 60 percent of the salmon and trout had at least one population or subspecies in trouble, while 22 percent of sunfishes — which includes the well-known species such as black bass, bluegill and rock bass — were listed. Even one of the most popular game species in the United States, striped bass, has populations on the list."

Some regions are more troubled than others. The Southeastern U.S., the mid-Pacific coast, the lower Rio Grande and Mexican watersheds that don't drain to the sea show particularly pronounced declines.

In the U.S., these areas areas were highlighted because they have high biodiversity and the greatest level of threat: