Issue 5

Don't Forget the Fish and Other Aquatic Organisms

by Kim MacQueen

We’re only human. When we think of water quality, we think first of drinking water—our drinking water. But the same principals for providing clean, clear water for human use also hold true for freshwater fish and other aquatic wildlife. For the fish, crayfish, mussels, and other animals making their home in the Southeastern United States, the difference between healthy and unhealthy water is the difference between life and death.

And there are a lot of them to consider. More than half the Nation’s freshwater fish live here. At nearly 600 species, they represent one of the world’s most diverse faunas. The South contains 165 fishes of concern in 14 different families, as well as rare darters, minnows, topminnows, dace, catfishes, and sculpins. Nearly 270, or 90 percent, of freshwater mussel species occur in the Southeast, the majority in the Tennessee River basin that curves through the middle of the region. Land use changes, channelization, sedimentation, and dam construction have severely affected the viability of this group of animals, which depend on freeflowing water to survive.

The crustacean fauna—mostly crayfish—is also broad and diverse, including 159 species of concern, 60 critically imperiled. Years of agricultural, industrial, and recreational use of forestlands challenges the fish, mussels, and crustaceans. Nearly all are threatened in some way by pollution, damming, sedimentation, and habitat loss.

As one might expect, practices that preserve intact forests produce the highest quality drinking water. They also provide the best habitat for aquatic species, regulating temperature and cleaning water as it percolates through the soil.

In recent years, Best Management Practices and improved road and stream crossing designs have helped keep sediment out of forest streams, but sediment is still a major problem for many aquatic species. Suspended sediment decreases water clarity and makes things difficult for animals trying to see to catch food. As sediment loads increase, fish gills can become clogged, growth rates reduced, and egg and larval development impeded. As sediment settles to the bottom of a stream or river, it can smother eggs and newly hatched larvae or fill in spaces that have provided habitat.

At the SRS Coldwater Streams and Trout Habitat unit in Blacksburg, VA, project leader Andy Dolloff collects and analyzes data from several long-term studies on the effects of water quality on brook trout and other species. One study, a joint effort with the University of Virginia, tracks the effect of acid rain—the infamous byproduct of human dependence on fossil fuels—on the area’s fish populations across several years.

“Water chemistry is one of the most important factors in fish production. When you have well-buffered water, you have greater fish production—with more fish species as well as more and larger individual fish,” Dolloff says. “In acidified water, production is decreased, with as few as one to three species present, plus slower growth and frequent failure of reproduction. Life for fish in an acidified stream is precarious.”

Many endemic—meaning native and narrowly localized—aquatic animals have adapted to the specific conditions in their home waters. That’s why, when human disturbance such as acid rain or excess sediment causes even slight changes in ph or sediment levels, entire populations can be wiped off the map.

That’s the story with many crayfishes. Entire species of these endemic crustaceans often live in areas no larger than a county. Susie Adams, a researcher with the SRS Center for Bottomland Hardwoods Research unit in Oxford, MS, studies a group that sticks to one specific area of the DeSoto National Forest, which is located in the hardwood bottoms of southeastern Mississippi. Adams has found that, in general, crayfish can adapt a bit faster to ecological disturbance than mussels or some fish. In a recent paper, Adams notes that crayfish populations tend to rebound fairly quickly following drought. And their relatively rapid lifecycle (about 2 years) means they get more chances to reproduce.

That’s not the case for freshwater mussels. Of 297 species found in the United States, 269 freshwater mussel species are found in the Southeast. Mel Warren and Wendell Haag, also with the SRS unit in Oxford, recently studied 26 species of freshwater mussels living in the Little South Fork of the Cumberland River, which flows through Kentucky and Tennessee. Two of these species were protected by the Endangered Species Act, one was a candidate for Federal protection, and 10 others were considered imperiled.

“The Little South Fork also supported a diverse fish fauna and, in general, was considered one of the highest quality upland stream systems in the Southeastern United States,” Warren notes. “However, beginning in the early 1980s, drastic mussel declines were documented in the lower Little South Fork, and the future of the stream as a mussel refugium for the Cumberland River system was uncertain.”

Strip mining along the lower Little South Fork during the 1970s and 1980s wiped out mussel populations there, but area residents—and Warren and Haag—believed the populations in the upper part of the river to be relatively unscathed. The area was remote and predominately forested, and enjoyed what they called a “protective blanket” of State and Federal statutes, regulations, and management agencies.

But that didn’t make any difference. Warren and Haag got to the field to begin data collection on the upper Little South Fork, expecting to find large mussel populations for a wide-ranging ecological study. But they hardly found any mussels at all. They’ve since surmised that oil drilling, which began along the upper portion of the river in the mid-1980s, had so disturbed the water quality that mussel populations began dying off before they could be studied.

“We had no idea this had happened in the upper river,” Haag remembers. “It took several days to process the information. It’s depressing as hell.” And that’s all too often just what researchers find when they look at specific point-source pollution in one narrow area. But it’s a little too easy to use this one study as a lens to look at what’s happening to freshwater animals everywhere.

“Sometimes we can tie declines of specific mussel populations to the construction of a dam, stream channelization, or pollution from a specific source,” says Haag, “but the worldwide patterns of decline in these animals implies that larger scale disturbances such as sedimentation and nonpoint-source pollution may have an equal impact.”

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For more information:

Andy Dolloff at 540-231-4864 or adolloff@fs.fed.us

Susie Adams at 662-234-2744, x267 or sadams01@fs.fed.us

Mel Warren at 662-234-2744, x246 or mwarren01@fs.fed.us

Wendell Haag at 662-234-2744, x245 or whaag@fs.fed.us

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Kim McQueen is a freelance science writer based in Brevard, NC.