National Geographic : 2010 Apr
animal species, including snails, mussels, croco- diles, turtles, amphibians, and sh. Almost half the 30,000 known species of sh live in lakes and rivers, and many aren't doing well; in North America, for instance, 39 percent of freshwater sh are imperiled, up from 20 percent only a few decades ago. Freshwater animals in general are disappearing at a rate four to six times as fast as animals on land or at sea. In the United States nearly half the 573 animals on the threatened and endangered list are freshwater species. That's because freshwater ecosystems are so closely linked to human activity. Industry and agriculture are concentrated alongside owing waters, and sooner or later the residue of virtually everything we do winds up run- ning down the nearest creek---if we haven't dried up the creek rst. In the southwestern U.S., as in other arid parts of the world, wild- life must compete for water with a burgeoning human population. Neither the Rio Grande nor the mighty Colorado is more than a trickle at its mouth today. But it is the American Southeast that stands out as a world center of freshwater-species di- versity, especially the southern Appalachian Mountains. Carved up into countless hills and hollows that are aglimmer with springs, ri es, rapids, smooth glides, and pools, the highly eroded mountains provided the isolated niches in which freshwater creatures could evolve into a multitude of forms. ey also escaped the Ice Age glaciers that bulldozed much of the con- tinent farther north. e result: e Southeast holds the grandest array of freshwater mussels on Earth; North America's premier collection of freshwater snails, cray sh, and turtles; and nearly 700 of the approximately 1,000 species and subspecies of U.S. freshwater sh. Like most freshwater sh, those of the South- east tend to be small and subdued in coloring--- for most of the year. If you dunk your head in SCAPHIRHYNCHUS ALBUS The pallid sturgeon, one of a group of fish that has endured since dinosaur times, has now lost much of its habitat along the Missouri River. Its mustache-like barbels sense chemical traces of its prey.