Southeastern Freshwater Fishes
STEPHEN J. WALSH, NOEL M. BURKHEAD, JAMES D. WILLIAMS
Florida-Caribbean Science Center, US Geological Survey
North America has the richest fauna of temperate freshwater fishes in the world, with about 800 native species in the waters of Canada and the United States. The center of this diversity is in the southeastern United States; where as many as 500 species may exist (62% of the continental fauna north of Mexico). Many coastal marine species also enter fresh waters of the Southeast, and at least 34 foreign fish species are established in the region.
Although freshwater fishes of the United States are better studied than any fish fauna of comparable scope in the world (Lee et al. 1980; Hocutt and Wiley 1986; Matthews and Hems 1987; Page and Burr 1991; Mayden 1992), large gaps exist in scientific knowledge about the biology and ecology of most species. New species are still being discovered, and the taxonomy of other species is being refined.
Seriously declining populations of freshwater fishes in the United States concern the scientific community (Deacon et al. 1979; Williams et al. 1989; Moyle and Leidy 1992; Warren and Burr 1994). This article briefly summarizes the current conservation status of southeastern freshwater fishes; the Southeast is emphasized because of its important fish biodiversity and to focus attention on the growing problem of adverse human impacts on the region's aquatic habitats (Mount 1986; Burkhead and Jenkins 1991; Etnier and Starnes 1991; Warren and Burr 1994).
Principal causes of declining fish resources in the Southeast are due to habitat perturbations. Such as loss of forested stream covet, mining activities, and impoundments, as at this site in northern Georgia.
The southeastern United States as defined here is delimited on the north and west by the Ohio and Mississippi rivers. The following hydrologic regions (Fig. 1) are defined on the basis of common geophysical characteristics and similar fish faunas of the drainages within each region (Hocutt and Wiley 1986): (a) Atlantic Slope-coastal waters from the Roanoke River (Virginia) southward to the Altamaha River (Georgia); (b) Peninsular- waters from the Satilla River (Georgia) to the Ochlockonee River (Florida); (c) Lower Apalachicola Basin-waters from the Apalachicola River (Florida) westward to the Perdido River (Alabama); (d) Lower Mobile Basin-lowland portions of the Tombighee and Alabama rivers and tributaries (Alabama and Mississippi); (e) Lower Mississippi-the Mississippi River and its eastern tributaries below the Ohio River (Mississippi, Tennessee, and Kentucky); (f) Interior Plateau-upland waters of the middle and lower Ohio River and southern tributaries, including the lower Cumberland and Tennessee rivers (Kentucky and Tennessee); and (g) Southern Appalachians
-upland waters of the mountains in the geo-logical provinces known as the Cumberland Plateau, Valley and Ridge, Blue Ridge, and Piedmont, south of the Kanawha (West Virginia) and Roanoke rivers. Many fishes are widely distributed in the Southeast and occur in two or more hydrologic regions.
Imperiled Freshwater Fishes
The Southeast has about 485 known species of native freshwater fishes, representing 27 families. Most of the diversity of the southeastern fish fauna is in five families: the darters and perches (family Percidae; 31.3%); the minnows (family Cyprinidae; 29.7%); the madtoms and bullhead catfishes (family Ictaluridae; 6.8%); the suckers (family Catostomidae; 6.6%); and the sunfishes and basses (family Centrarchidae; 5.8%). The greatest diversity is in the Appalachian Mountains and Interior Plateau (Fig. 1), but other regions of the Southeast also harbor many more species than do similar-sized geographic areas elsewhere in the United States.
Fig. 1. Total numbers of freshwater fishes and percentage imperiled by hydrographic region of the southeastern United States.
As of January 1994 the U.S. Fish and Wildlife Service (USFWS) had designated 15 southeastern fish species as endangered and 12 as threatened, representing 6% of the entire regional fish fauna. Ninety-three fish taxa (19%) are imperiled (endangered, threatened, or of special concern) in the Southeast, including proposed listings and those recognized by other authors (Williams et al. 1989). During the past 25 years, only seven species were upgraded by the USFWS, mainly because of discovery of new populations, inadequate knowledge at the time of listing, or invalid taxonomy. No endangered or threatened species have been delisted. A steady upward trend in designation of imperiled southeastern fishes has occurred in the last 20 years (Fig. 2); the number of species considered imperiled by the USFWS increased from 3 (less than 1%) in 1974 to 84 (17%) in 1994 (USFWS listings only). During the 10-year period from 1979 to 1989, the number of species considered imperiled by the American Fisheries Society increased from 63 (13%) to 81 (17%; Fig. 2).
Fig. 2. Total numbers of imperiled fishes in the Southeast during the last 20 years, as recognized by the American Fisheries Society (AFS) and the U.S. Fish and Wildlife Service (USFWS). Numbers represent imperiled species during years of listing activity.
An alarming 21% of the nearly 300 species of minnows and darters are imperiled in the Southeast. Considered alone, more than 30% of the 150 species of darters are in trouble, representing the highest total number of species in any one family. Madtom catfishes (genus Noturus
) are also disproportionally imperiled among large families of more than 30 species (Etnier and Starnes 1991; Warren and Burr 1994). Among smaller groups of fishes, the most severe status is among the sturgeons and paddlefish, where seven of the eight (86%) southeastern species are in jeopardy. In terms of ecological requirements, most imperiled species are those that live in small to large creeks and small rivers, are closely associated with clean stream-bottom substrates, or are isolated in spring and cave environments.
On a regional scale, the greatest number of imperiled species occurs in the highland areas of the Appalachians and Interior Plateau, followed by the Coastal Plain subregions (Fig. 1). This geographic trend is correlated with both a high level of diversity in the respective hydrologic regions and the quite localized or endemic distributions of many species. Especially important are a number of watersheds that harbor many species confined within those drainages; these watersheds include the Tennessee River, the Mobile Basin, the Cumberland River, and the Roanoke and James rivers (Warren and Burr 1994). Most jeopardized species have restricted distributions, but the number of more geographically widespread species that are disappearing from large portions of their ranges is increasing.
Two species of southeastern fishes have become extinct in the last century: the harelip sucker (Moxostoma lacerum
) and the whiteline topminnow (Fundulus albolineatus
). At least one other species, the darter (Etheostoma microperca
), has disappeared from the southern portion of its range that falls within the region covered here. The slender chub (Erimystax cahni
) has not been seen since 1987 and may be near extinction. Two other species peripheral to the Southeast are feared extinct: the Scioto madtom (Noturus trautinani
) and the Maryland darter (Etheostoma sellare
; Etnier 1994).
Tangerine darter (Percina aurantiaca).
Mountain redbelly dace (Phoxinus oreas).
The declining status of freshwater fishes among divergent taxonomic groups and across broad habitat types and geographic areas is interpreted as evidence for widespread and pervasive threats to the entire North American fish fauna (Moyle and Leidy 1992; Warren and Burr 1994). In the Southeast, fish declines are the result of the same factors that cause global deterioration of aquatic resources, primarily habitat loss and degraded environmental conditions. The principal causes of freshwater fish imperilment in the Southeast and other areas of the United States are dams and channelization of large rivers, urbanization, agriculture, deforestation, erosion, pollution, introduced species, and the cumulative effects of all these factors (Moyle and Leidy 1992; Warren and Burr 1994). The most insidious threat to southeastern fishes is sedimentation and siltation resulting from poor land-use patterns that eliminate suitable habitat required by many bottom-dwelling species. Cumulative effects of physical habitat modifications have caused widespread fragmentation of many fish populations in the Southeast (Fig. 3), presenting difficult challenges for those trying to reverse and restore diminished fish stocks.
Fig. 3. An example of habitat fragmentation, decline, and isolation of populations of a southeastern freshwater fish, the endangered spotfin chub (Cyprinehla monacha). Former (pre-1930's)
and present range in yellow.
Aquatic resources are often resilient and capable of recovery, given favorable conditions. Conservation of southeastern fishes will require significant changes in land management and socioeconomic factors (Moyle and Leidy 1992; Warren and Burr 1994), but such changes are necessary to stem future losses of biodiversity. The first step required is to improve public education on the value and status of native aquatic organisms. For resource managers and policy makers, increased efforts must be made to assume proactive management of entire watersheds and ecosystems; establish networks of aquatic preserves; restore degraded habitats; establish long-term research, inventory, and monitoring programs on fishes; and adopt improved environmental ethics concerning aquatic ecosystems (Warren and Burr 1994). The southeastern fish fauna is a national treasure of biodiversity that is imminently threatened. If this precious heritage is to be passed on, its stewardship must be improved through cooperative actions of all public and private sectors within the region.
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S.J. Walsh, N.M. Burkhead, and J.D. Williams. 1995. Southeastern Freshwater Fishes, p.144-147 in LaRoe, E.T., G.S. Farris, C.E. Puckett, P.D. Doran, and M.J. Mac eds., Our Living Resources: a Report to the Nation on the Distribution, Abundance and Helth of U.S. Plants, Animals, and Ecosysytems. U.S. Department of the Interior, National Biological Service, Washington, DC, 530 p.
For further information:
Stephen J. Walsh
Florida-Caribbean Science Center
US Geological Survey
7920 NW 71st St.
Gainesville, FL 32653-3073