Rivers: Dams, Canals and Channeling: Page 2 Endangered Species Handbook

Aquatic Ecosystems

Rivers: Dams, Canals and Channeling: Page 2

With a total of 297 species, North America has the world's greatest diversity of freshwater mussels, though they have suffered dramatic declines as a result of dams (Neves 1996). Free-flowing rivers and streams have been turned to ponds, and to compound the damage, the dam builders usually channel rivers downstream. Using machines with revolving chopping blades, natural, curving rivers and streams are converted into straight ditches. Stream edges are cleared of vegetation, and river bottoms are dredged, depositing mollusks and crustaceans in piles along the banks. What is left is a sea of mud in a ditch devoid of life. Malacologist Dr. George M. Davis (1977) concludes these projects, combined with acid drainage from strip mining, erosion and pesticide runoff from agriculture, have been the major causes for the near-extinction of much of the continent's native mollusk fauna (Davis 1977). At least 102 species are considered threatened in the United States, 97 percent of these from habitat loss or degradation (Stein et al. 2000).

Prior to the devastation of their habitats, mussels clustered in vast numbers on river bottoms throughout the major rivers and their tributaries in the Midwest and southeastern United States. These rivers meandered through forests that provided cool shade. River otters, muskrats and mink denned among tangled tree roots and in banksides. Water quality remained clear as a result of the forests and the filtering actions of the mussels. River snails fed on the detritus and algae of the mussel shoal, further cleansing the water. The mussel shells formed large, reef-like piles on river bottoms, providing habitat for fish, crayfish, water plants and large river snails. Turtles, aquatic birds and mammals fed on the fish, mussels, snails and crayfish in this ecosystem.

A major center of diversity for these mussels is Alabama, which has more than 235,000 miles of waterways and three major river basins left untouched by Pleistocene glaciers, preserving a great diversity of species (Stein and Flack 1997). Having survived the Ice Age, many species of mussels, fish and crayfish became extinct or endangered when water projects began destroying their habitats in the 1920s. The richest of all known beds, Mussel Shoals, located in the Tennessee River of Alabama, once had a diversity of approximately 70 mussel species. The Wilson Dam, completed in 1924, submerged Mussel Shoals and covered them with 15 to 20 feet of mud, causing the extinction of at least half the mussel species and five of the seven large river snails (Davis 1977). Experts at the University of Alabama in Tuscaloosa report 69 percent of mussel species are extinct, endangered, threatened or of special concern in the rivers and streams of the state (Cushman 1995b).

Many mussel species need small fish to complete their reproductive cycles. One threatened mollusk, the orange-nacre mucket (Lampsilis perovalis) of the Mobile River basin, produces larvae that resemble tiny fish; they anchor to the adult mussel with a long, wavy mucous strand that acts as a lure to tiny fish; when a fish attempts to eat this larva, however, it breaks away and attaches to the fish's body (Hartfield and Butler 1996). The fish carries the mussel larvae to a new area. Other mussels have different reproductive strategies. In some cases, fish congregating around the beds are parasitized by embryonic mussels who cling to their fins or gills and become enclosed in a cyst. The larvae absorb nutrients from the fish for two or three weeks, growing into juvenile mussels, and in the process, they are transported to new areas, where they detach and colonize stream beds (Hartfield and Butler 1996).

The orange-nacre mucket is one of many species that have disappeared from most major rivers, and only small streams and creeks now afford suitable habitats for the creature (Hartfield and Butler 1996). The host species for many mussels are darters. These fish exhibit a rainbow of iridescent hues in a multitude of patterns. Many of their names are evocative of their color or origin: Amber (Percina antesella), Bayou (Etheostoma rubrum), Goldline (Percina aurolineata), Slackwater (Etheostoma boschungi), Watercress (Etheostoma nuchale) and Okaloosa Darters (Etheostoma okaloosae). All the latter species are listed on the Endangered Species Act.

The most famous of these little fish is the 3-inch snail darter (Percina tanasi). Named after the river snails upon which it feeds, this species was discovered on the Little Tennessee River in 1973 above the Tellico Dam site after construction of this major dam by the Tennessee Valley Authority (TVA) had begun. Construction continued after the TVA was able to reverse preliminary injunctions to delay the dam brought by conservationists and irate Tennessee residents being evicted from their land. By the time the snail darter was scientifically described, proposed and listed under the Endangered Species Act, the dam was nearly complete. There is evidence that construction was hastened when word of the fish's discovery became known, in order to prevent conservationists from stopping the dam. The snail darter's survival is due to transplants into other parts of the Little Tennessee River and a few of its tributaries and its discovery in 1980 on a new site in Tennessee’s South Chickamauga Creek, by Dr. David Etnier of the University of Tennessee, who originally discovered the species. The snail darter is now known to exist in Alabama and Georgia, as well as Tennessee. It has been reclassified as threatened under the Endangered Species Act. It does not owe its existence to the TVA, however, which destroyed its only known habitat with a dam, nor to Congress, which rewrote the Endangered Species Act to sanction the extinction of this and other species that might impede "development."

Over three hundred types of crayfish are found in the United States; these species make up 61 percent of the 525 crayfish species found worldwide (Stein et al. 2000). Most species live in rivers, streams and waterways in the southeast (Clancy 1997). These crustaceans share many of the same ecosystems inhabited by mussels, darters and snails, and about half the species are threatened with extinction (Stein and Flack 1997). Hiding in crevices, under rocks and buried in sand, crayfish attempt to escape herons, raccoons, river otters and predatory fish (Clancy 1997). A 1996 study by the American Fisheries Society found 65 species of crayfish living in a single river drainage (Clancy 1997). They are usually only 3 or 4 inches long, and like lobsters and shrimp, females carry fertilized eggs attached to the underside of their abdomen. Even after hatching, she allows them to cling to her abdomen for several weeks before they become independent (Clancy 1997).

Native crayfish have declined along with mussels and fish in the altered environments created by dams and channeling. Only four crayfish species out of more than 150 species considered imperiled by The Nature Conservancy are listed on the Endangered Species Act, and almost nothing has been done for their preservation (Clancy 1997). The Nature Conservancy has programs to educate people to protect the land around streams from pollution from cattle, and it is building partnerships with local, rural organizations and conservation groups. The goal of their programs is to preserve the habitats of native crayfish and hundreds of other species by arresting water pollution and other misuses of waterways. This benefits the local economies in the process.

Mussels, crayfish and darters are important indicators of environmental quality because of their great sensitivity to changes in water quality. Scientists have warned a mass extinction of American mussels and crayfish is imminent. Public interest is sparse for these endangered species, lacking the popularity of the bald eagle, the gray wolf or even the black-footed ferret. Yet they are critical to the healthy functioning of southeastern aquatic ecosystems and represent a precious source of diversity on the continent.

The damming of southern rivers continued in the 1960s and 1970s. By 1967, there were nine dams on the Tennessee River, leaving only 22 miles free-flowing. The last un-dammed river in Tennessee, the Duck River, was dammed in 1975. It contained the greatest diversity of snail species left in the Tennessee-Ohio River system (Davis 1977). The Fish and Wildlife Service listed seven species of endangered mollusks native to the Duck River on the Endangered Species Act when the Columbia Dam was under construction. In retaliation, the TVA brought an unsuccessful lawsuit against the Department of the Interior (FWS 1979). Besides the biological impoverishment resulting from destruction of natural rivers and streams, many potential food sources for humans are lost, such as mussels, crayfish and fish.

For fish of rivers in the US West, the opposite conditions prevailed. Flowing through desert landscapes, these rivers tend to be warm and turbid from eroded soil. The Colorado River evolved an extremely rich, endemic fish diversity adapted to this water type. During the 20th century it was dammed throughout its course. Dam operators of the 49 dams on this river occasionally release water from these reservoirs. Coming from the bottom of the reserves, the icy, cold water inundates ecosystems below, creating habitats that endanger native fish. Among these endangered fish are the humpback chub (Gila cypha), the Colorado squawfish (Ptychocheilus lucius) and razorback sucker (Xyrauchen texanus). The Colorado squawfish, a large fish reaching 6 feet, was once an important food fish for natives and settlers. None of these species have been able to adjust to the cold, clear waters of the dammed Colorado River, which prevented their free movement. The Fish and Wildlife Service has artificially maintained these and other endangered fish in hatcheries, and some populations survive in un-dammed tributaries. Dams on the Colorado River have also inundated precious riverside habitats of small marshes where rare water birds bred. The delta of the Colorado River was once a vast marsh in northern Mexico, a wildlife haven which harbored millions of waterfowl and fish. It was the life blood of the Cocopa tribe. As a result of the dams and diversion of its water to Los Angeles and for local agriculture, the delta is now a mere trickle. The silt that was once deposited on banks and in the delta is now retained upstream, depriving ecosystems downstream of nutrients.

Although the rate at which natural rivers are being dammed has slowed considerably in recent years, for many species the damage has been done. A growing number of organizations and individuals have been urging the removal of dams, especially those causing extinctions. The McPherri Dam on a tributary of the Sacramento River, which once had one of the largest salmon runs in the state, was demolished in 1998, and a few days later, another dam in Medford, Ore., was breached (Egan 1998). A dam on Maine's Kennebec River was removed in 1999, allowing salmon and other fish to return to former haunts. This required the work of many conservationists for more than a decade, and many politicians and others in the state opposed its removal. The 75,000 US dams were often built at huge public expense. Congressional representatives have pushed these projects through Congress for decades, promoted without real analysis of need, economic benefit or environmental effect. Some of the larger dams may be more difficult to remove. The dams on the lower Snake River in the Northwest, for example, have eliminated the millions of salmon that once spawned here, affecting wildlife and local economies. A major effort to breach these dams to allow passage of salmon is gaining momentum, but many barge operators and farmers who transport their grain to market on the barges are strongly opposing the breaching of these dams. In the future, dams may be regarded with less respect as naturally flowing rivers become better appreciated. As former Secretary of the Interior Bruce Babbitt said while commencing the destruction of a dam: "Dams are not like the pyramids of Egypt that stand for eternity. They are instruments that should be judged by the health of the rivers to which they belong" (Egan 1998). Breaching is a compromise to removal of dams that may be more acceptable to dam defenders.