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Aquatic Species

Southeastern aquatic animal diversity is globally significant. A recurring theme in the chapters edited by Benz and Collins (1997) is that, although the importance of the aquatic diversity of the Southeastern United States is well known to biologists, there is still much that we don’t know. Although the worldwide biodiversity crisis is well publicized, very little is known about aquatic systems, especially the exceptional diversity indigenous to North America. The lists of rare aquatic animals included in this Assessment should be considered as indicators of the groups as a whole, and not as inclusive lists. Lydeard and Mayden (1995) suggested that protecting habitats important to a majority of southeastern aquatic animals would result in conservation of a high proportion (more than 80 percent) of North American aquatic biodiversity. Next, we focus on what is known of geographical distribution patterns and biological characteristics that make these rare species vulnerable.

Important life-history characteristics, including feeding, reproduction, and escape mechanisms, are reviewed for each taxonomic group. These characteristics govern the sensitivity of organisms to ecological stressors, especially sediment, during the most critical stages in their life histories. Fish are too diverse in their life histories to include in a single group and have been split into families for analysis.

Crustaceans—The 159 rare crustaceans included in this Assessment (table 23.4) belong to three orders: (1) decapods (containing shrimp and crayfishes), (2) isopods (sowbugs), and (3) amphipods (sideswimmers, or scuds) (NatureServe 2000, Pennak 1989) (fig. 23.2). Although Shuster (1997) commented that there is not enough known about many crustacean groups to make a determination about conservation status, we include species in this Assessment for which there are enough available data to indicate their rarity. All of these rare crustaceans are scavengers feeding on dead or dying animals and plants. The females of these three orders protect their eggs and young by retaining them in a marsupial pouch until they reach their first instar.

Habitats used by crustaceans include four broad aquatic habitat types: (1) caves and subterranean streams, (2) ponds, (3) burrows in stream or pond banks or in wet meadows, and (4) streams. Figure 23.3 displays the proportion of species associated with each habitat type.

Some crayfish excavate burrows, which provide protection from dehydration during dry periods (Hobbs 1976, 1989; Pflieger 1996). Burrowing crayfish are often found along stream or pond edges, but they may occur at great distances from open water in moist pastures or lawns (Pennak 1989, Pflieger 1996). The pond and stream-dwelling crayfish include burrowers and nonburrowers (Hobbs 1989), but even stream-dwelling crayfish that normally don’t burrow can excavate burrows if their stream dries out. The stream-dwelling crayfish spend daylight hours hidden under rocks or organic debris in the stream channel, emerging at night to forage (Hobbs 1989). The isopods, the amphipods considered here, and 24 of the crayfish are restricted to caves and springs.

Available data indicate that these rare species are not geographically clustered but are evenly distributed around the South (fig. 23.4), except in western Texas and Oklahoma, which are devoid of rare crustaceans. Crustaceans in general, as well as the southeastern species included in this Assessment, are among the most narrowly endemic organisms known (Taylor and others 1996). For example, of the 159 species discussed in this Assessment, 144 are known from relatively small geographical areas (fig. 23.5).

Threats to crustaceans—The extremely restricted ranges of many crustaceans amplify the effects of even relatively small-scale impacts. Taylor and others (1996) noted, “Taxa restricted in range to an area of 100 square miles or less are particularly vulnerable to habitat destruction or degradation . . . .” Any degradation severe enough to cause extirpation could also cause total extinction.

For example, three of the four pond-dwelling crayfish listed in table 23.4 are known from a single locality, while the range of the fourth is restricted to only a slightly larger area. However, these crayfish may tolerate periodic desiccation of the ponds they live in because they can burrow if the ponds dry (Hobbs 1989).

In addition to pollution and habitat alteration, threats to stream-dwelling crayfish include overcollecting for bait or food, competition from exotic crayfish, and predation from introduced (stocked) fish (NatureServe 2000, Taylor and others 1996). Another nonnative pest species, the zebra mussel, can attach so densely to crayfish that the crayfish are unable to shed their carapaces and grow (Schuster 1997).

The rare groundwater inhabiting species of isopods, amphipods, and crayfish are being impacted by dewatering of aquifers, pollution, and sedimentation.

Future for crustaceans—Regardless of the preferred habitat, the viability of many of the rare crustaceans is most threatened because of their small ranges. Impacts to habitats that would reduce or extirpate local populations of other taxonomic groups might result in extinction of some crustaceans (Taylor and others 1996). Crayfish are somewhat tolerant of desiccation, but permanent conversion of wetlands to pasture or urban uses could eliminate populations and lead to extinctions. Best management practices directed at the protection of wetlands and riparian areas will increase the potential viability of these species.

Areas that contain nonnative crayfish associated with “bait-bucket” introductions could see the natives continue to decline (Taylor and others 1996).

Insects—The 176 rare aquatic insects (table 23.5) addressed in this Assessment include organisms from five separate orders: (1) Plecoptera (stoneflies, 64 species), (2) Ephemeraoptera (mayflies, 15 species), (3) Odonata (dragonflies, 31 species, and damselflies, 4 species), (4) Trichoptera (caddisflies, 60 species), and (5) Coleoptera (aquatic beetles, 2 species) (Meritt and Cummins 1984) (fig. 23.6). These organisms use all five habitat types but are predominately found in rivers and streams (fig. 23.7). With the exception of the two beetle species, all of the adult insects considered in this Assessment are terrestrial, returning to the aquatic environment only to deposit eggs.

The stoneflies are most often associated with flowing water where they seek hiding cover among rocks, algae, and organic debris. They are very sensitive to low oxygen levels. Eggs are released into the water column or attached to underwater structures. Once the nymphs hatch, they spend from 1 to 3 years in the water. Most nymphs are carnivorous, feeding on aquatic insects; however, some species feed on algae, bacteria, and vegetable detritus (Pennak 1989).

Mayflies are very similar to stoneflies in their habitats and preferred habitats. Most species in this group, however, are herbivorous. Some species are carnivorous, while others feed on organic detritus (Pennak 1989).

Dragonflies and damselflies are similar to each other in many of their habitat needs (Meritt and Cummins 1984). They are sight feeders, feeding on insects, worms, small crustaceans, and mollusks, and cannot feed adequately in turbid water. Depending on the species and water temperature, nymphs may spend a few months to several years in the water (Pennak 1989).

The caddisflies typically produce one or two generations per year. In most species, the adult female enters the water and swims to the bottom to attach eggs to the substrate. Many nymphs build elaborate cases to provide protection and attachment. Feeding strategies include grazers and scrapers that feed on algae and detritus attached to rocks; strainers and net filters that collect suspended organic matter from the water column; and carnivores that feed on insect, worms, and small crustaceans (Pennak 1989).

The aquatic larvae life stage of the two beetle species listed in table 23.5 are restricted to springs and subterranean flows associated with Edward’s aquifer in central Texas (NatureServe 2001). These larvae crawl along the bottom feeding on algae and plant detritus. In addition, since neither species is capable of flight, the adults are also closely linked to these aquatic habitats, and dispersal is limited to water movement through the aquifer (Pennak 1989).

Morse and others (1997) noted that insects are generally small, cryptic, little-known animals. Few biologists are expert in their identification or ecological requirements. In their discussion of rare southeastern insects, Morse and others included a list of dragonflies and damselflies, mayflies, stoneflies, and caddisflies. These groups are apparently better known than some other groups of aquatic insects (Harris and others 1991, Wiggins 1977, for example).

With the exception of the narrow endemics, whose geographic ranges are relatively small, the insects are wide ranging, with their distributions often including several States. However, these large ranges frequently include vast areas of unoccupied habitats; the areas currently occupied by these insects are often highly localized. Because the adults can be far ranging and more mobile than many of the other aquatic animals discussed in this Assessment, they are likely to reoccupy areas where they have been previously extirpated (NatureServe 2001). County occurrence data are not available for most of these species; consequently, no distribution map could be produced.

Threats to insects—Because of restricted geographic ranges, or highly localized populations of wide-ranging species, the insects are subject to extinction from any factors that alter their habitats severely enough to extirpate single populations. In addition to water pollution, or other factors that affect food organisms, runoff that results in increased turbidity could interfere with sight-feeding ability and adversely affect these predatory insects.

Sediment can also affect filter-feeding caddisflies, some of which require stable stream bottoms with spaces among rocks for attachment of filter nets. Many caddisflies, stoneflies, mayflies, and other insect larvae require sediment-free surfaces for grazing and prey production.

Although biological threats are not listed for the beetles, the USFWS (U.S. Federal Register 1997) stated, “The primary factor threatening the long-term survival of these species is availability of a sufficient quantity of water to maintain essential characteristics of their habitat.”

Factors that can affect aquatic insects in general include runoff, including sediment and chemicals from agricultural, silvicultural, and urban activities. Other threats include water-quality degradation from fish farms, and exotic pests that affect trees on streamsides. Forest harvests also can produce other changes that could affect stream-dwelling insects. For example, a change in plant community composition may reduce the amount of large woody debris in streams, a change in the processing rate of organic matter, or lowered quality of food (leaves) that falls into the stream to be “processed” by insects (Morse and others 1997). These changes could affect the entire food web.

Future for insects—The riverine insects have lost a considerable amount of habitat as a result of dams and reservoirs. The remaining populations are often isolated from each other by great distances, making dispersal and genetic exchange difficult or impossible. Some intervening habitats, which may be suitable, are unoccupied for unknown reasons. Three odonate species are restricted to single populations, and the loss of any of these populations would amount to extinction of the species. Better information about the distribution of all rare odonates is needed. To ensure long-term viability of all stream-dwelling insects, measures that improve and maintain water and habitat quality are needed.

The insects restricted to springs and other groundwater habitats are threatened by water withdrawal that dewaters the aquifers, by pollutants (that can become concentrated as ground water is lowered), and by other activities that directly affect spring habitats.

Snails—The 123 freshwater snails (table 23.6) (fig. 23.8) included in this Assessment are classified into two groups: Pulmonata (7 species) and Prosobranchia (116 species) (Hart and Fuller 1974). Members of the order Pulmonata are related to terrestrial snails and are capable of breathing air, which allows them to exist in water containing low levels of oxygen (Hart and Fuller 1974). Five of these, including one lake dweller and two stream dwellers, are presumed to be extinct. The two remaining species are known from swift-flowing water (Hart and Fuller 1974).

Members of the order Prosobranchia are related to marine snails and have internal gills that help them obtain oxygen from the water (Hart and Fuller 1974). All 22 of the spring or cave species and 94 of the stream-dwelling snails belong to this group. Figure 23.9 displays the habitats utilized by rare snail species.

Snails feed on algae and detritus, which are scraped from rocks, vegetation, and other substrates (Pennak 1989). Life cycles typically range from 1 to 3 years; most species have annual life cycles (Pennak 1989). Reproduction varies among species. The majority of species are egg layers, but some are live-bearers (Hart and Fuller 1974).

The distribution of rare aquatic snails is highly localized; most of the stream-dwelling snails are indigenous to the Tennessee or Mobile River systems (fig. 23.10). One rare species is found in lakes in Virginia. Others are known from springs and caves: 14 species in Florida, 3 in Texas, 2 in Kentucky, and 1 each in Arkansas, Virginia, and Alabama.

Threats to snails—Threats to the viability of these rare snails are associated with impacts to their preferred habitats. For example, the Piedmont pondsnail was known from only one pond. It apparently became extinct because cattle were allowed access to the pond for watering (NatureServe 2000).

Many of the 100 stream-dependent snail species are historically known from small geographic areas, even single riffles, and therefore have been threatened by dams. For example, a series of dams on the Coosa River is believed to have caused the immediate extinction of at least 20 snail species (Lydeard and Mayden 1995). Any existing populations of these stream-dwelling snails are physically isolated by reservoirs (U.S. Department of the Interior, Fish and Wildlife Service 2000). At least 89 of the 100 rare snails that prefer streams are concentrated in the Tennessee and Mobile River systems (fig. 23.10). In North America, at least 36 species of snails are thought to have become extinct since European settlement began; all are from the Mobile River system (Lydeard and Mayden 1995). Exotic species, including zebra mussels, are threats to the remaining stream-dwelling populations of rare snails (Hart and Fuller 1974).

A major threat is sedimentation. It can inhibit growth of algae on which snails graze (Neves and others 1997), accelerate erosion of snail shells, and affect survival of eggs (Hart and Fuller 1974). Although scant information on toxicity is available, other pollution events, such as chemical spills, are potential threats to aquatic gastropods (Hart and Fuller 1974, Neves and others 1997).

Future for snails—The single lake-dwelling snail species listed in this Assessment is considered extinct. The narrowly endemic Piedmont pondsnail was apparently formerly restricted to a single lake. It appears to have been destroyed by cattle (NatureServe 2000), but water pollution, sedimentation, or an accidental spill could have produced the same result.

Fourteen of the 22 rare snails associated with springs and caves are found in Florida. All of these species are narrow endemics, often restricted to a single spring (NatureServe 2000). In Florida, the major threats to spring and cave systems are sewage seepage and sedimentation (Petranka 1998). Presently, aquifer drawdown is apparently not a significant threat to the Florida spring systems, but in Texas, it may be the single most important threat (NatureServe 2000). As with all narrow endemics, the magnitude of potential threats to a single population needs to be respected.

Mussels—The 191 rare mussels (table 23.7) evaluated are not divided into subgroups based on taxonomy. They use only river and stream habitats (fig. 23.11). The primary and secondary habitats of each mussel were determined from distribution records and specific references (Dennis 1985; NatureServe 2001; Parmalee and Bogan 1998; U.S. Department of the Interior, Fish and Wildlife Service 1992, 2000; Williams and others 1993). No rare mussels were found to be dependent on groundwater habitats, lakes, or ponds.

Freshwater mussels respire and feed by siphoning water across their gills; food consists of microorganisms and organic particles (Parmalee and Bogan 1998).

Reproduction is extraordinarily complex. Males release sperm into the stream; sperm are siphoned out, and fertilization occurs within the females. The eggs mature into larvae known as glochidia, which are released into the water and become encysted on a fish host that is often very specific. Varieties of mechanisms have been developed to ensure that the glochidia reach the appropriate host (Parmalee and Bogan 1998). While parasitizing the fish host, the glochidium transforms into a juvenile mussel. After detaching from the fish, the juvenile mussels take up residence in the stream bottom.

The rare mussels are distributed among 11 major watersheds or groups of watersheds spread across the South (fig. 23.12). This grouping is based on the unionid faunal provinces summarized in Parmalee and Bogan (1998). Almost 80 percent (148 of 191 species) of these rare mussels are endemic to single watersheds.

The Cumberland watershed is home to 60 of the 191 rare mussels evaluated in this Assessment. Historically, the Tennessee and Cumberland River systems had the most diverse mussel fauna in the South (Hughes and Parmalee 1999, Parmalee and Bogan 1998). Although inhabitants of shallow shoals in larger rivers have probably declined the most (Neves and others 1997), some species remain in scattered localities where riverine habitat remains, but they are isolated by dams and reservoirs (Parmalee and Bogan 1998).

Another important area for mussels is the Mobile River basin, which ranks among the top 10 river basins in the World in terms of historical diversity of freshwater mussels (Lydeard and Mayden 1995, U.S. Department of the Interior, Fish and Wildlife Service 2000). Today these imperiled species are found in relatively clean river reaches isolated by degraded reaches or reservoirs (U.S. Department of the Interior, Fish and Wildlife Service 2000).

Other important areas for mussels include the Mississippi watershed; the Apalachicola, Ochlockonee, and Suwannee River watersheds; and the South Atlantic Rivers (fig. 23.12).

Threats to mussels—The threats to viability of freshwater mussels are many and compounding in their impacts. Parmalee and Bogan (1998) stated, “The greatest overall detrimental impact on mussel populations probably can be attributed, directly or indirectly, to dam construction—especially those built in the 1930s, 1940s and 1950s.” Numerous recovery plans published by the U.S. Department of the Interior, Fish and Wildlife Service (Ahlstedt 1983, U.S. Department of the Interior, Fish and Wildlife Service 2000) also identify dams as the most important factor in the decline of mussels.

The most direct effect of dams on mussels is the immediate loss of flowing water upstream of the dam site. Once their habitat is inundated by a reservoir, the mussels living there are unable to move to suitable riverine habitat. In addition, reproduction will not occur if the fish host is similarly adapted to riverine environments. Bogan (1993) described mussels stranded in reservoirs as “functionally extinct when the host fish is no longer present.” Although, historically, subpopulations of the same species may have been separated by several miles in a river, their dispersal schemes (glochidia attached to more mobile fish), allowed the flow of genes between the cohorts. Currently, subpopulations that are separated by a few miles are often genetically isolated by dams.

The plight of these mussels is aggravated by the accumulation of sediment that would normally move through the system. Because flow is often restricted in reservoirs, sediment can settle and accumulate.

To adequately consider the habitat needs of freshwater mussels, it is important to include the needs of their fish hosts. Freshwater mussels spend some time as a parasitic larva (glochidia) attached to the gills or fins of various fish species. The fish hosts for many of the rare mussels are unknown (Ahlstedt 1983); however, this aspect of freshwater mussel ecology is being actively researched (Neves and others 1997). Turbid water may inhibit the sight-feeding fish hosts, which must find the glochidia (NatureServe 2001). Therefore, for riverine fauna to remain viable, measures to reduce the amount of sediment that reaches the bottom habitats in streams are necessary.

Transportation and accumulation of sediment occur in all river habitats. The principal sources of sediment to rivers and their relative level of significance are discussed in detail in chapter 19.

Sediment can clog gills of mussels, reducing feeding efficiency and interfering with mussel and host fish interactions. Heavy sediment loads can also potentially smother individual mussels. Sediments result from agricultural, silvicultural, mining, urban development, road construction, and other activities on the land (Neves and others 1997). According to Neves and others (1997), agriculture is the most widely reported source of pollutants. Streamside buffer strips can significantly reduce soil and nutrient concentrations in surface runoff.

In addition to this sediment threat in the Southeastern United States, excessive nutrients and pesticides from intensive agriculture or silviculture could affect mussels. Although mussels can close their valves to avoid short-term exposure to pollutants, the effects of chronic exposures are mostly unknown. Neves and others (1997) emphasized the need to set water-quality criteria by using early life-history stages for toxicity testing. Other pollutants potentially affecting mussels include petroleum spills, industrial discharges, and highway salts (Abell and others 2000, Hart and Fuller 1974, Neves and others 1997). Coal mining can produce sediment runoff and alter water chemistry with acid drainage and heavy metals (Neves and others 1997).

On many large and medium-sized rivers, continual dredging is often necessary to maintain an appropriate channel for barge traffic (Abell and others 2000). Dredging can make the river substrate unstable and unsuitable for mussels (Hart and Fuller 1974). On smaller streams, relocating or straightening channels can reduce habitat diversity and stability of the bottom substrates. Dredging can also remove mussels from their beds. Commercial sand and gravel dredging operations can have similar effects (Neves and others 1997).

Water withdrawals can sometimes compound these threats, especially in small streams. Because they have less volume of water, small streams often are exposed to higher concentrations of pollutants than larger streams. Water withdrawals for rural and urban uses may also reduce base flows of small streams, shrinking available mussel habitat (Abell and others 2000).

Two exotic mussel species, Asian clams and zebra mussels, directly compete with native mussels for food and space, especially in reservoirs and large rivers (Bogan 1993). Zebra mussels may attach to native mussels in large enough numbers to weaken or kill the natives. Zebra mussels (living and dead) may also accumulate in such densities that they significantly alter the physical characteristics of the substrate as well as the water quality.

Future for mussels—The ways in which mussel habitats are affected by human activities vary little between watersheds; consequently, this Assessment focuses on stream size without emphasis on drainage unit.

The long-term status of many river mussels is undetermined at present. Neves and others (1997) stated, “Because mussels are thought to be the longest lived freshwater invertebrates, with a longevity of more than 100 years for some species, population declines may continue for decades. Thus, the extirpation of species is a prolonged event, lagging decades behind the directly responsible factors of attrition of the fauna.”

The system of dams along the 650 miles of the Tennessee River from Knoxville, TN, to Paducah, KY, was designed so that even at the lowest operating pool level, the water behind one dam backed up to the next (Ungate 1990), essentially eliminating any free-flowing water. Flow of the Cumberland and Mobile Rivers is similarly restricted (U.S. Department of the Interior, Fish and Wildlife Service 2000). However, there are still some relatively riverine sections of these systems. The methods of operating the dams can improve downstream water and habitat quality, providing additional habitat (Yeager 1993).

In free-flowing segments of rivers, mussel communities may be wholly or partially intact, but the populations probably have become genetically isolated from other populations of the same species. Chance events probably also take a toll on these isolated populations, which have no natural means of being augmented and little habitat suitable for expansion. Many rare mussel species that depend on river habitats may not be able to sustain themselves. However, recent advances in technology have stimulated proposals for augmenting or reintroducing captively propagated individuals (U.S. Federal Register 2001a) in some of these large river habitats.

Rare mussels that are typically found in stream habitats are subject to the same environmental impacts as mussels in the rivers, but they could be affected more severely by changes in water quality and quantity. For example, streams are more often affected by road and railroad crossings, and roads that parallel their courses. The likelihood for accidental spills from trucks or trains is high. Chemical spills pose a serious threat to many isolated mussel populations. Fish hosts and mussel glochidia may be more susceptible to acute toxicity than adult mussels (Rand and Petrocelli 1985), but adult mussels may be more susceptible to chronic exposures, especially those from materials that accumulate in their bodies (Fridell 1996).

Urban and agricultural pesticides enter river systems either directly as they are sprayed onto the body of water or indirectly as residues attached to soil particles that wash into the stream following a storm (U.S. Department of Agriculture, Forest Service 1989). Some of these pesticides, such as 2,4-D, are known to be extremely toxic to fish and many invertebrates (Johnson and Finley 1980, Mayer and Ellersieck 1986). Yet, the potential toxicity of these chemicals to the majority of mussel or fish (host) species is unknown. However, recent advances in technology that improve captive production of mussels may allow for toxicity testing to more accurately set water-quality standards (Neves and others 1997). The effects of agricultural chemicals on the reproductive success of mussels also need to be researched. Minuscule amounts of pesticide may mimic natural hormones (Neves and others 1997). This threat is difficult to recognize because adult mussels may remain in the river for years without reproducing.

Mining, chemical, manufacturing, and wood-product wastes entering rivers from point sources are subject to environmental reviews for permitting and monitoring (Fridell 1996). However, water-quality standards used in this permitting usually are not based on toxicity testing of rare species. Mussels and their fish hosts may be more sensitive than the organisms tested to establish the standards. Therefore, permitted activities may indeed affect the rare mussels and fish. Threats to water quality can also arise when retention ponds are overwhelmed by a storm. The chemical wastes associated with these activities could have direct and immediate effects on the fish and mussels, and some of these toxicants may persist for months or even years. As suggested above, the ability to captively produce enough individuals of the more sensitive aquatic species to use in setting water-quality standards could improve this situation.

Water withdrawals for domestic, agricultural, or industrial uses diminish the wetted stream bottom and could reduce available habitat for mussels and their host fishes. Although typically, there are limits on individual withdrawals and minimum flow requirements, demands for water are increasing in the South.

Fish—Like most of the other aquatic animal groups discussed here, the Southeastern United States is well known by biologists for its high diversity of freshwater fish (Warren and others 1997, 2000). Nearly half of the North American fish fauna is found in this region (Warren and others 2000). Etnier (1994) noted that only two southern fish (hairlip sucker, Moxostoma lacerum, and whiteline topminnow, Fundulus albolineatus) are known to be extinct. Two others (Scioto madtom, Noturus trautmani, and Maryland darter, Etheostoma sellare) are also believed to be probably extinct. The Southeast also contains a high proportion of fish currently considered jeopardized. Warren and others (2000) listed 28 percent of the 662 native freshwater or diadromous southern fish as jeopardized. They noted this was a 75-percent increase in the proportion of jeopardized fish since 1989, and 125 percent since 1979. Although there are still gaps in knowledge, freshwater fish are better known than many other aquatic animals discussed in this Assessment. Etnier (1994) pointed out that, even though we have relatively more data on southeastern freshwater fish than some other groups, our knowledge is still inadequate to accurately assess the status of many, possibly declining fish. He recommended more long-term monitoring efforts.

The 165 rare fish assessed (table 23.8) belong to 14 families (fig. 23.13). Rivers, streams, and groundwater habitats are the major habitats where they occur most often (fig. 23.14).

Etnier and Starnes (1991) noted that darters and madtom catfish are more likely to be jeopardized than would be expected, based on their representation in the fauna. These groups of fish have highly specialized reproductive requirements, which probably also contribute to their sensitivity. Angermeier (1995) also noted that ecological specialists are more extinction-prone than are generalists. These animals normally have life-history requirements that include the use of crevices beneath or between rocks and a clean stream bottom. Darters (63 of the fishes discussed here) occupy a wide variety of habitats ranging from small springs to fast-flowing riffles in large rivers to backwater areas in swamps (Burr and Warren 1986. Etnier and Starnes 1993, Jenkins and Burkhead 1993, Pflieger 1975, Smith-Vaniz 1968). Many darters are considered clean-water species (Etnier and Starnes 1993) that are sensitive to sedimentation. Most are sight feeders and many species care for their eggs and young. Like many other groups previously discussed, some darter species are restricted to relatively small geographical areas, often a single watershed (Etnier and Starnes 1993, Jenkins and Burkhead 1993, Warren and others 2000).

Minnows (46 species discussed here) are generally sight feeders, taking microorganisms and organic matter from the water column. Reproductive activities range from spawning in association with nests built by a larger minnow, placing eggs in crevices in rocks or logs, and attaching eggs to submerged plants or gravel (Etnier and Starnes 1993). Although some minnows protect their nests, many eggs are scattered or attached and left alone. Some rare minnows are geographically restricted to small watersheds.

The 16 rare catfish included in this Assessment are predominately madtoms. Spawning occurs beneath rocks or other objects on or near the substrate. Eggs and young are guarded by the males and are well protected (Burr and Stoeckel 1999, Etnier and Starnes 1993). Most catfish are nocturnal feeders, relying on their highly sensitive barbels to detect aquatic insects. They also apparently rely heavily on “taste” or “smell” to find mates or make other observations about what goes on in their waters (Todd 1973). The rare madtoms, headwater catfish, and spotted bullhead are found in small to medium-sized streams; many species have highly localized populations. The two cave catfish included here are found in groundwater systems restricted to Edward’s Aquifer in Texas. All of these catfish are endemic with highly localized populations (Burr and Stoeckel 1999).

Seven suckers are included in this Assessment. These fish use small to large streams. They feed on invertebrates that they stir up by nudging their heads into gravel and cobble streambeds (Etnier and Starnes 1993). Therefore, a loose substrate is essential for their foraging. Spawning occurs in similar areas; eggs are buried beneath the gravel and cobbles, which are disturbed by the tail movements of the fish. Some species build rough nests, but no parental protection is provided for the eggs or fry (Etnier and Starnes 1993).

The sturgeons included in this Assessment (six species) are all relatively long-lived fish that can reach a large size. They are prized for their flesh and eggs (Etnier and Starnes 1993), although the Federal protection status of most of the species listed in this Assessment does not allow for legal harvest. Sturgeons are bottom feeders, using their barbels to find food organisms, which include crayfish, mussels, snails, and insects (Jenkins and Burkhead 1993). Spawning migrations may cover more than 100 miles; individual fish do not spawn every year, and sexual maturity may not be reached until the fish is 14 to 30 years old (Jenkins and Burkhead 1993). Spawning occurs in shallow water, and no parental care is provided to the eggs or fry (Etnier and Starnes 1993). Several of these characteristics, including late maturity and infrequency of spawning, render all the sturgeon species exceptionally vulnerable.

The five species of live-bearers included in this Assessment are restricted to warmwater springs and spring runs in Texas (NatureServe 2000). Two of these species are believed to be nearing extinction, if they aren’t already extinct (Williams and others 1989). These fish are all midwater feeders, taking insects, amphipods, filamentous algae, and young fish (Lee and others 1980). Spawning can take place year round. In comparison with most other fishes, which hatch from eggs, possess a large yolk sac, and are relatively helpless for a while, live-bearer young are born fully developed (Lee and others 1980).

Four rare species of topminnows and studfish are included in this Assessment. All of these species prefer small streams, springs, or the margins of rivers and are closely associated with cover (Etnier and Starnes 1993). They feed near the surface on invertebrates. All spawn over a substrate of rock or attach their eggs among vegetation; no parental care to the eggs or fry is provided (Etnier and Starnes 1993).

The four pygmy sunfish included in the Assessment prefer springs, spring runs, or blackwater swamps, where they feed on crustaceans (Etnier and Starnes 1993, NatureServe 2000). The life spans of most pygmy sunfish species are probably not much longer than 1 year (Etnier and Starnes 1993). The distributions of several species are geographically isolated, and some are found in only a few localities (Rohde and Arndt 1987).

The four sculpin evaluated in this Assessment are restricted to small, coldwater streams or springs. Three are found in headwaters of the Tennessee River drainage in Virginia, and one is found in a single spring in the Mobile River basin in Alabama (Jenkins and Burkhead 1993, Mettee and others 1996). All four are narrow endemics occupying very small geographic areas. Sculpins are predators. They feed on aquatic insect larvae, crayfish, and fish, usually ambushing their prey at night from beneath the cover of rocks (Jenkins and Burkhead 1993). Spawning takes place in cavities under rocks excavated by males (Jenkins and Burkhead 1993). The males care for the eggs until they hatch (Etnier and Starnes 1993).

The bass and sunfish evaluated in this Assessment include three black bass and one rockbass. These all prefer small to medium-sized streams (Lee and others 1980), where they feed on crayfish, other invertebrates, and small fish (Jenkins and Burkhead 1993). Males construct nests and provide protection for their eggs and fry (Lee and others 1980). All of these species are considered sport fish.

Two of the three pupfish evaluated are restricted to springs; the others occur in streams (NatureServe 2000). All three are endemic to Texas. These small fish may exist in loose gravel when no surface water is present. They spawn over gravel; the male defends a territory, but does not provide any protection for the eggs. Food includes microscopic benthic organisms (NatureServe 2000).

The three cavefish are all narrow endemics restricted to cave systems in the Mississippi, Cumberland, and Ozark watersheds. They feed on copepods, crayfish, salamanders, and their young (Pflieger 1975). Spawning activity has not been documented; however, Etnier and Starnes (1993) speculate that they may be mouth brooders.

The Waccamaw silverside is the only silverside included in this Assessment. This species probably only lives for about 1 year (Shute 1997). Silversides are upper-water residents that school in large numbers. They feed on small, planktonic invertebrates and are believed to spawn in open water, providing no protection for the eggs or young (NatureServe 2000). This fish is especially vulnerable because of its short lifespan, and because it is a narrow endemic, being restricted to a single lake in North Carolina.

The distribution of rare fish across the South (fig. 23.15) is remarkably similar to the rare mussel distribution. In fact, the three watersheds (Cumberland, Mississippi, and Mobile) with the highest number of rare mussels and rare fish are the same. The South Atlantic and Apalachicola are also high for both species groups. The Rio Grande is a significant watershed for rare fish.

Threats to fish—Threats to fish are many, cumulative, and interactive. The most frequent explanation for declines in southern fish is habitat alteration, which has affected all habitat types (Etnier 1997, Warren and others 1997, Williams and others 1989). Physical habitat alteration resulting from impoundment, channelization, dredging, sedimentation, ditch cleaning, and other changes that result from land treatments could affect darters, minnows, catfish, bass, pygmy sunfish, and sculpins, for example (Warren and others 2000).

Many of the fish (excluding the wider-ranging minnows, herrings, suckers, and sturgeons) considered in this Assessment have apparently always been narrow endemics (Warren and others 2000). Others currently exist in fragmented populations because of habitat alterations. Consequently, the small, isolated populations that remain are subject to extinction from a few or even a single natural chance or accidental event.

Reservoirs have flooded much of the preferred habitats for fish in at least six of the family groups discussed here. For example, the Amistad gambusia went extinct when Amistad Reservoir flooded its only known location (NatureServe 2000). However, in spite of the many reservoirs found throughout the South, many populations of sensitive fishes still exist (Etnier 1994). Populations remaining are often widely separated and therefore much more vulnerable to single catastrophic events (Angermeier 1995, Warren and others 2000). Dams have also blocked migration routes for suckers, herrings, and sturgeons.

Chronic buildup of sediments and prolonged periods of turbidity can adversely affect feeding, spawning, and cover availability. Sight feeders, such as the rare Conasauga logperch, forage by flipping rocks over with their snouts and feeding on the aquatic insects found on the bottom of the rock they have just flipped. Rocks imbedded in silt are not easily moved, and they support fewer aquatic invertebrates for darters and other fishes that feed similarly (Etnier and Starnes 1993). Since most darters and madtoms and some of the other fishes included here (suckers and some minnows) deposit their eggs on or near the substrate, sediment buildup impacts their spawning success. Many darters also seek cover from predators in the spaces between rocks. Sediment fills these spaces and eliminates the essential cover.

In addition, many other sensitive fish discussed in this Assessment are especially vulnerable to impacts of human activities simply because of their life histories. For example, some sturgeons do not become sexually mature until they are 15 to 30 years old (Etnier and Starnes 1993), and then they only reproduce periodically, exposing themselves to years of habitat alterations and pollution, and potential harvest by humans before they are even able to produce offspring. Conversely, some other fishes are extremely short-lived. For example, the pygmy sunfish and the Waccamaw silverside seldom live for more than 1 year (Jenkins and Burkhead 1993, Rohde and Arndt 1987, Shute 1997). If some factor results in poor reproductive success during a single spawning season, the entire population could be lost.

Pollution and sediment threats from mining, industrial, and agricultural activities; accidental spills; and urban expansion have already, or potentially could, impact most of the fish family groups or their food resources (Warren and others 2000). Sediment reduces available food organisms and may inhibit maturation of eggs, especially for crevice-spawning minnows or species with bottom-dwelling larvae and young, like madtoms, darters, and some minnows. For other animal groups, developing water-quality standards based on toxicity testing of more sensitive fish species could improve this situation.

Water withdrawal resulting in aquifer drawdown and contamination of ground water is potentially a serious threat to spring and cave-adapted species (Elliott 2000, Etnier 1997, Etnier and Starnes 1991, Hubbs 1995, Warren and others 2000). These sensitive fish include some of the topminnows, pupfish, live-bearers, and cavefish. Animals living in these habitats are more vulnerable to pollution and sedimentation, because of their inability to adapt to water quality and habitat changes in their relatively stable environments.

While not as obvious in the Southeast as in the Western United States, introductions of nonnative fishes can result from stocking, bait-bucket releases, and interbasin connections (Nico and Fuller 1999, Sheldon 1988). Competition from introduced species threatens some topminnows, pupfish, bass, and live-bearers; hybridization is a potential threat to some darters, minnows, topminnows, pupfish, and bass. Predation from introduced species threatens darters, suckers, madtom catfishes, and silversides (NatureServe 2000). The San Marcos gambusia, a live-bearer, apparently was forced into extinction from a combination of events including competition and hybridization (NatureServe 2000).

Overharvesting and collecting for bait or aquarium trade are affecting or have affected suckers, bass, pygmy sunfish, sturgeon, topminnows, pupfish, and cavefish (NatureServe 2000).

Future for fish—Many of the rare darters included here are narrowly endemic species subject to catastrophic losses from relatively minor accidents or chance events. A single spill of toxic chemicals could drastically reduce or eliminate a population. Therefore, protecting important stream-bottom habitats and water quality by preventing runoff and spills is important to ensure their continued existence. Because these populations are geographically isolated and reinvasions are not likely because of habitat barriers, augmentation or reintroduction may be necessary to ensure existence of some species.

In comparison with many fish discussed above, distributions of most of the rare minnows considered in this Assessment are somewhat broader, but their populations have often been fragmented. For many minnow species, so little is known about requirements for various life stages that real threats and reasons for rarity are speculative. Dams, reservoirs, and other unknown factors have adversely altered habitat or water quality, resulting in isolated populations of some minnows, like the spotfin chub and blue shiner. Population augmentation or reintroduction may be necessary to improve the probability of long-term existence for some species.

Etnier and Starnes (1991) concluded that, although the madtoms are a disproportionately jeopardized part of Tennessee’s fish, they are not largely confined to habitats that are more jeopardized than any others. Their specialized reproductive requirements and their probable sensitivity to trace chemicals (“olfactory noise;” see Etnier and Jenkins 1980) are likely major factors in their vulnerability. In addition, many of the madtoms included here, as well as the headwater catfish and the spotted bullhead, are narrow endemics, or currently exist as fragmented populations that are only portions of formerly more widespread geographic distributions. This habitat fragmentation also increases their vulnerability (Angermeier 1995). As with all species that have very limited ranges, any losses could be catastrophic, and could result from relatively minor accidents or events.

Sediment and pollutants that reduce the amount of available food or interfere with chemical communication could be detrimental to these catfish. In addition, although males protect eggs and young, chronic sedimentation can lead to heavy imbeddedness of the stream bottom, and greatly reduce the amount of suitable spawning sites. Measures that protect and improve habitat and water quality in streams where these fish are known to occur would increase the likelihood of their continued existence. Frequent, regular monitoring should be conducted, and population augmentation or reintroduction has been recommended for some species (Rakes and others 1999, Shute and others 1997).

Most of the rare sucker species included here are relatively large in comparison with the other groups of fishes discussed. The large number of individuals concentrated together during spawning runs and the noted quality of their flesh have made suckers a valuable food item for hundreds of years. Intensive harvesting by Native Americans and later by generations of Americans, however, apparently did not greatly reduce sucker populations. Only after the dams blocked their migration routes and altered flowing-river habitats did some sucker species experience declines. Postimpoundment declines may have resulted from overharvest because of the suckers being concentrated below the dams.

Suckers need an unconsolidated substrate for foraging. Chronic sedimentation causes stream bottoms to become imbedded with silt, making foraging more difficult and successful spawning less likely. In addition, nonnative predators, especially the flathead and blue catfish, decrease the survival of young suckers (NatureServe 2000). Measures to control sedimentation, careful management of nonnative fish, and, where appropriate, measures to assist in fish passage could ensure long-term survival of rare suckers.

The rare sturgeons are all large, long-lived fish. The very long period before reaching reproductive maturity and dams that block migration routes have led to declines. Most of the species discussed in this Assessment currently receive some form of Federal protection, either listing or candidate for listing, and they are not legally harvestable, although all sturgeons have historically been considered sport fish. Their continued survival will be contingent on reestablishing spawning runs and protecting immature fish. Like many large river mussels, these long-lived, big river fish may continue to exist, but if their habitats and migration routes have been destroyed, they may not persist without human intervention. In areas where appropriate habitats exist or are restored, reintroduction or population augmentation may be important management techniques for ensuring the long-term viability of these fishes.

The five live-bearers listed here are all narrowly endemic to warmwater springs. Two are either believed to be already extinct, and three are federally listed and in imminent danger of extinction. One was eliminated by the construction of a reservoir over its spring. The other was lost to herbicide pollution, competition, and eventual hybridization (NatureServe 2000). The other three live-bearers are currently facing these same threats, in addition to drawdown of the aquifers where they exist. The long-term survival of these species in the wild depends on managing the entire aquifers where the live-bearers occur, with careful consideration for the needs of these endemic fish.

The topminnows and studfish are also narrow endemics associated with a series of springs, or short stream sections. Groundwater drawdown has significantly impacted some of these fish, especially the Barrens topminnow. Collection for bait or aquarium trade may have also reduced the numbers of some populations, but was probably only a significant factor when droughts caused them to be concentrated in small areas. Captive breeding programs and long-term plans for water supply and use in the areas affecting these fishes would help to ensure their long-term survival.

The pygmy sunfish listed here are found in heavily vegetated springs, swamps, roadside ditches, and small streams. They are most vulnerable because of their short lifespan. Removing vegetation from the areas where they occur also threatens their continued existence.

The sculpins listed here are all narrow endemics found in small headwater streams or cold springs. Although the pygmy sculpin, found in a single spring, is potentially threatened by groundwater contamination and aquifer drawdown, the spring is used as a town water supply, and the fish is currently carefully monitored. However, because it is restricted to such a small geographic area, it is vulnerable.

The headwater sculpin species are threatened by commercial and residential development. Chronic sedimentation could reduce their food supply or interfere with reproduction. Although populations of these fish exist in small geographic areas, they are relatively abundant where they are found. Activities that improve or maintain habitat and water quality would help ensure their continued existence.

The bass are all narrow endemics. They are potentially threatened with hybridization or competition, to a lesser extent, with nonnative fish. Fishing pressure could affect these species.

The pupfish listed here are all narrow endemics. The three pupfish are endemic to small geographically isolated areas in Texas; two are restricted to springs where impoundments and aquifer drawdown have had significant adverse impacts (Elliott 2000, NatureServe 2000). Sheepshead minnows, not native to the areas where the pupfish are found, have been introduced and compete with or hybridize with all three species. Water pollution has also affected the Pecos pupfish. Potential for long-term survival of the two spring-inhabiting species of pupfish in the wild is low.

The cavefish are all narrow endemics. In addition to their endemism, the cavefish are threatened by life histories that result in extremely low population numbers (Hobbs 1992).

Chemical, nonpoint-source water pollution associated with agriculture and urban development could contribute to declines in these sensitive fish. Surface aquifer recharge areas may contribute chemicals that disrupt the essential chemoreception in blind cavefishes.

The Waccamaw silverside is restricted to Lake Waccamaw. Its short lifespan, just over 1 year, makes it vulnerable to unsuccessful spawning in a single season. The water quality in this lake is affected by nutrient loading from shoreline homes, agriculture, and intensive timber harvesting in the swamps surrounding the lake (Shute 1997). The recent natural invasion of the native brook silverside into Lake Waccamaw may pose a threat from competition to the Waccamaw silverside, but the likelihood of this is unknown at present [Personal communication. J.R. Shute (no personal communication information available at this time)].

The Alabama shad is a marine species that migrates into major rivers to spawn. Dams have blocked many rivers, preventing extensive spawning runs.

Amphibians—Dodd (1997) noted that, although some amphibian populations are known to fluctuate substantially from year to year, few long-term data sets exist to document whether this is a natural occurrence. As mentioned for other groups of aquatic animals, assessing conservation status is difficult without this information. Therefore, until better information is available, the list of rare amphibians included in this discussion should be considered only a representative sample of threatened species.

The 31 rare amphibians (table 23.9) include 2 frogs, 1 toad, and 28 salamanders (fig. 23.16). Two species (the toad and one salamander) are terrestrial as adults but lay their eggs in ephemeral ponds. The other 29 species use the aquatic environment year round, including the breeding season. The primary habitats where these amphibians are found are shown in fig. 23.17. Rivers and lakes are not frequently used by any of the rare amphibians included here. Sixteen of the nineteen salamanders discussed are associated with subterranean streams and springs of the Edward’s Aquifer in central Texas.

Most amphibians are predators feeding primarily on invertebrates as adults and larvae (tadpoles) (Petranka 1998). Female salamanders of some species protect their eggs. The frogs and toad lay their eggs in ponds and abandon them. The flatwoods salamander lays its eggs in areas that are likely to be temporarily flooded after heavy rains (Petranka 1998).

The rare amphibians included in this Assessment are not distributed uniformly across the South. Figure 23.18 shows three significant clusters of amphibian occurrences. The first cluster is in central Texas, principally the Edward’s Aquifer, where groundwater habitats support a variety of species. A second cluster along the Appalachian Mountains is the result of several geographically restricted salamander species associated with flowing streams and streamside habitats. A third concentration of rare amphibian occurrences extends across the Florida panhandle, where salamanders, newts, and an amphiuma are the species of concern. Dodd (1997) noted the same areas of importance, and included the Edward’s Plateau and the Interior Highlands as important areas for amphibian diversity.

Threats to amphibians—Amphibians are subject to a variety of direct and indirect threats to survival, including bait collecting (Benz and Collins 1997, U.S. Department of Agriculture, Forest Service 2001), removal of mature hardwood trees along streams (Petranka 1998), intensive ground-disturbing activities associated with timber extraction (Petranka 1998, Petranka and others 1994), and acid rain (Petranka 1998). Dodd (1997) suggested that the different life-history stages (eggs, larvae, young, adults) might have different sensitivities to environmental perturbations.

Several rare amphibians primarily associated with perennial streams and streamside habitats are especially vulnerable because of their geographically restricted distributions (Petranka 1998). In addition, removing beaver has reduced the number of southern wetland habitats (Herrig and Bass 1998, White and Wilds 1997), further isolating many amphibian populations. Dodd (1997) also noted that if population fluctuations reported for some amphibians are natural, small, isolated populations might be especially at risk.

Subterranean species are sensitive to sedimentation and to seepage of even small quantities of chemicals or nutrients into the aquifers (Elliott 2000, Petranka 1998).

Amphibians associated with perennial streams and streamsides are affected by the removal of riparian vegetation; thus they would benefit from the careful management of appropriately sized buffer strips.

Amphibians associated with ephemeral ponds on the Atlantic and Gulf Coastal Plains are threatened by changes in hydrology brought on by intensified forest management and agricultural or urban development. In these areas, wetlands used by these amphibians are often altered by deliberately draining land with perched water tables (Miwa and others 1999, Segal and others 1987) or through indirect effects of other intensive land management activities (Palis 1996, Petranka 1998, Vickers and others 1985). Herbicides used in conjunction with timber harvests may also affect amphibians, but as with many other groups discussed here, sensitivity of amphibians to chemicals is largely unknown (Dodd 1997). Dodd (1997) noted that forest community changes associated with silvicultural activities such as conversion of deciduous forests to pine forests could result in reduced amphibian diversity.

Other factors that may affect rare amphibians include water-quality changes because of mining, acid precipitation, or runoff from road cuts. Changes in pH may have adverse effects, especially on eggs and larval stages, and can inhibit growth and feeding (Dodd 1997). Other chemical pollutants are known to mimic hormones, and thus may interfere with reproductive success (Dodd 1997). Ultraviolet light (UVB) is also known to affect larval hatching success. This effect is compounded by low pH (Dodd 1997).

Roads can have several adverse effects, including acting as barriers that prevent adults from migrating between nonbreeding and breeding habitats. Noise and light associated with roads may also interfere with the ability of frogs and toads to hear calls or to see and catch prey (Dodd 1997). Many rare amphibians use terrestrial habitats; they are discussed in chapter 1 and chapter 5.

Future for amphibians—Sixteen of the nineteen salamanders included here are associated with subterranean streams and springs. These species are dependent on the Edward’s Aquifer in central Texas and are affected by rapid agricultural and urban growth in this area. Although the only known location for the Valdina Farms sinkhole salamander has been flooded by a reservoir, and the species may no longer exist (NatureServe 2000), the more common threat to the salamanders in this region is water withdrawal from Edward’s Aquifer.

Three additional subterranean or spring-associated salamanders are included in this Assessment. One is known from northern Oklahoma and Arkansas, another from southern Tennessee and northern Alabama, and the third from southwestern Georgia and northern Florida. All three of these species are apparently far less threatened than are their Texas counterparts. However, like other subterranean species, sedimentation and seepage of even small quantities of chemicals or nutrients into the aquifers could pose significant threats to their continued existence (Petranka 1998).

The amphibians associated with perennial streams and streamsides include six salamanders restricted to small geographic areas in the Southern Appalachian Mountains, two salamanders and a frog restricted to the Gulf Coastal Plain, and a salamander from the Atlantic Coastal Plain in North Carolina. Because of their restricted ranges, these amphibians are all vulnerable to relatively small disturbances, which may further isolate populations. Perturbations could result from intensive ground-disturbing activities associated with timber harvesting, altering wetlands, and stream sedimentation (Petranka 1998).

Herrig and Bass (1998) demonstrated the importance of the dispersal mechanism that beaver ponds provided to amphibians, prior to the beaver’s extirpation in the 1700s. Because of the greatly diminished riparian habitat provided by beavers, gene dispersal between salamander populations is restricted in some areas. Another threat is the collection of salamanders for bait (Petranka 1998), which often happens with little regard to species. Acid precipitation and sedimentation in streams may also contribute to the decline of some salamanders in this region. All six of these stream-dwelling salamanders are located primarily on land administered by the National Park Service and the USDA Forest Service.

Three rare salamanders and a frog are associated with perennial streams and streamsides near the Gulf and Atlantic Coasts. They are most affected by the removal of riparian vegetation. In addition, as discussed earlier, the small number of beaver ponds present in these areas restricts gene flow between populations. Maintenance of streamside buffers would increase the likelihood of long-term existence of these amphibians.

The final group of amphibians includes four salamanders, a frog, and a toad, all of which are associated with ephemeral ponds. Land management activities that result in rapid runoff instead of retention of standing pools of water are detrimental to these species. For example, the flatwoods salamander and the Houston toad have suffered significant range reductions brought on by certain land management activities, including land clearing, ditching, draining and filling of wetlands, and hydrological alteration brought on by mechanical disturbance of the soil (Jensen 1999, NatureServe 2000, Petranka 1998). Restoring and protecting important ephemeral ponds may be necessary to ensure the continued existence of the flatwoods salamander (U.S. Federal Register, April 1, 1999). Land uses that alter habitats required by the flatwoods salamander threaten the species.

The Texas Parks and Wildlife Department now manages two preserves for the recovery of the Houston toad (Fostey 2001), which should ensure the survival of this species, at least for the short term. The other four remaining species of ephemeral pond-dwelling amphibians (three salamanders and one frog) have apparently not been affected as severely as those discussed earlier.

Reptiles—Although Buhlmann and Gibbons (1997) reported that historical information needed to accurately determine the status of many North American aquatic reptiles is lacking, they concluded that more than half of the southeastern aquatic reptile fauna is jeopardized. Because of this lack of information, the list included in this Assessment should probably be considered as only an indicator of the trends in southeastern aquatic reptile status. However, Buhlmann and Gibbons (1997) noted that the Southeast contains North America’s greatest diversity of freshwater turtles.

The 19 rare reptiles (table 23.10) discussed here include 1 crocodile, 4 snakes, and 14 turtles (fig. 23.19). These reptiles are typically found in flowing rivers or calm waters of swamps and bogs (fig. 23.20); none are known to depend on groundwater habitats or lake habitats. Most of these reptiles require basking sites such as logs or boulders that protrude from the water. Except for the live-bearing snakes of the genus Nerodia, all of these reptiles require undisturbed gravel bars or soft banks for egg laying (Wilson 1995). Most of these rare reptiles are long-lived and require several years to reach sexual maturity (White and Wilds 1997).

Invertebrates, fish, and amphibians are their main food items. An exception is the Alabama redbelly turtle, an herbivore that feeds on aquatic plants (NatureServe 2000, U.S. Department of the Interior, Fish and Wildlife Service 2000, Wilson 1995).

Two areas in the South are known to have concentrations of rare reptiles (fig. 23.21). One area in west Texas includes the Rio Grande and Pecos River systems, and another extends from central and southern Mississippi into the panhandle of Florida (fig. 23.21) (NatureServe 2000). Other rare reptile occurrences are scattered throughout southern Florida, the Southern Appalachian Mountains, western Tennessee and Kentucky, and central Texas (Wilson 1995).

Threats to reptiles—Many rare reptiles are long-lived, narrow endemics (Palmer and Braswell 1995, Wilson 1995) and are subject to extinction from natural chance events or even localized human activities. Seemingly inconsequential activities, such as riding an off-road vehicle on a streambank, collecting a few turtle eggs for the pet trade, or “plinking” at basking turtles, may in fact be devastating to species whose populations are isolated and which may have already experienced severe population declines. However, in comparison with the other aquatic animals included in this Assessment, these reptiles may be relatively resilient to or capable of adapting to habitat changes (NatureServe 2000). Buhlmann and Gibbons (1997) emphasized the lack of ecological knowledge about many aquatic reptiles; they could be more vulnerable than we know. Certain aspects of their life histories could be easily disrupted, resulting in population declines. Two species that are not narrowly endemic are the copperbelly water snake and bog turtle, which both have relatively widespread but spotty distributions. Thus, they are also subject to extinction from natural chance events or localized human activities.

The illegal pet trade also could have a significant impact on some of these reptile populations (Buhlmann and Gibbons 1997), especially those of small turtles. Overharvest for food (largely for Asian markets) could have significant impacts on some turtles. Some harvest is apparently legal, but poorly regulated (Buhlmann and Gibbons 1997). Target practice results in the death or injury of many rare turtles and snakes (NatureServe 2000).

Pollution and sediment may impact all of these species directly or indirectly through a reduction in their food organisms (NatureServe 2000). The 16 egg-laying species are potentially affected by direct disturbances to their nests (Conant and Collins 1998). Most nests are close to water; the eggs often remain buried for months. Off-road vehicle riding, trampling, or other human activities could destroy these nests (NatureServe 2000).

The reptiles that prefer flowing water have been impacted by dams, channelization, and dredging (NatureServe 2000). These activities often remove logs that extend out of the water, which are essential basking sites. The Texas species have also been impacted by water withdrawal (NatureServe 2000).

The species that prefer standing water in bogs or swamps have lost habitat because of wetland alterations, removal of basking logs, and loss of beaver ponds (Herrig and Bass 1998, NatureServe 2000).

Future for reptiles—The loss of beaver and the wetlands they create has greatly reduced the available habitat for bog turtles and copperbelly water snakes. Natural range expansion and genetic dispersal for these species requires an interconnection of suitable aquatic habitats (Herrig and Bass 1998). However, since beaver are increasing in the South, these situations may improve.

Removing water for irrigation, industrial, and urban uses; lowering stream flows; and pollution resulting from agricultural practices have contributed to the decline of rare aquatic reptiles in Texas (NatureServe 2000). Development and implementation of management plans to provide appropriate amounts and quality of water would increase the long-term survival potential for these species.

Identification and protection of important nesting areas along waterways would improve the future prospects of these long-lived reptiles.