Duskytail Darter

Etheostoma percnurum

Description

This slender bodied, 2.5-in (6.35-cm) fish has a straw to olivaceous colored body, the top of the head is medium to dark gray, and the belly is dingy white to pale gray. It has 10-15 long dark vertical bars on the sides of its body, 38-48 (usually 40-45) lateral scales, and 17-20 (usually 18-19) dorsal spines and rays. It is difficult to determine the sex of non-breeding individuals in the field. However, during the breeding season, the males become very distinctive. The head becomes dark and swollen, and the humeral spot and lateral vertical bars intensify. The first dorsal saddle and vertical bar form a particularly intense dark yoke. A dark border of melanophore develops along the pectoral and anal fin margins, and the anal fin whitens proximally. Brilliant gold, fleshy knobs develop on the tips of the dorsal fin spines and are conspicuous in contrast to the clear medial and dark basal portions of the fin membrane.

Behavior

The duskytail is primarily an insectivore. The youngest individuals consume microcrustaceans, chironomid larvae, and sometimes large quantities of heptageniid nymphs. Larger individuals are also mainly benthic insectivores, but they generally feed on larger prey items, such chironomid larvae, ephemeropteran nymphs, microcrustaceans, and trichopteran larvae. Heptageniids were the dominant food item in the three largest duskytail size classes examined, and large duskytails sometimes feed on fish eggs. Because heptageniids occupy the interstices between rocks, duskytails may feed on the undersides of rocks. In the Little River, the spawning season occurs from late April or early May through June. In Copper Creek, the earliest spawning was observed as early as April 6 but most spawning occurs in May. Water temperatures were between 63.5 and 75ÞF (17.5 and 23.9ÞC). In the Little River, spawning occurs within the same habitat that the species occupies during the rest of the year. Many apparently breeding adults have been observed in a gravel/rubble run with moderate current in Copper Creek. In Citico Creek, nests and nest-guarding males have been found beneath slab rocks in the margins of pool areas, and in relatively swift shallow water in run areas, as long as appropriately sized slab rocks were available for nest cover.

Prior to the spawning act, the male chooses and cleans a spawning site under a rock. The male chases the female into the nest cavity, both fish invert their bodies, and the eggs are deposited individually into an egg cluster on the underside of the nest rock. Males stay at the nest site, guard the eggs, and may spawn with multiple females. The result is a clutch of 23-150 eggs. After several days, to allow for more ova to mature, the female can spawn with other males. Duskytail darters can spawn as one-year olds. About half of the individuals spawn at one year of age and do not survive to spawn again. The individuals that survive to spawn as two-year olds die shortly after spawning, and a very small percentage of the Little River population survived to age three.

Habitat

The duskytail darter inhabits gently flowing shallow pools and eddy areas of large creeks and moderately large rivers in the Tennessee and Cumberland River systems.

This species' distribution overlaps the Oak-Hickory ecosystem and Nashville basin. The elevation is about 6,400 ft (1,950 m). Most of the outer part of the basin is deeply dissected and consists of steep slopes between narrow rolling ridgetops and narrow valleys. The inner part of the basin is predominantly undulating and rolling. The average annual precipitation is about 35-45 in (89-114 cm). The soils of this ecosystem are varied, have a thermic temperature regime, an udic moisture regime, and a clay subsoil.

The duskytail inhabits the edges of gently flowing shallow pools, eddy areas, and slow runs in usually clear water of large creeks and moderately large rivers. Snorkel observations in Citico Creek and in the Little River, Copper Creek, and the Big South Fork of the Cumberland River indicate that they are apparently very discriminatory about preferred microhabitat type, being found over heterogeneous mixtures of rock sizes from pea gravel, rubble/cobble, slab-rock, and boulder substrates. The water is shallow, 4-30 in (10-76 cm) deep, with slow runs around edges of pools. Substrates are heterogeneous, with a wide range of rock sizes from pea gravel to cobble, slabrock, and boulders.

This apparent preference for a mixture of various substrate sizes often results in patchy distributions. There may be locally dense clumps of individuals within a relatively short distance, and then long stretches can be surveyed without observing a single specimen. Adult duskytail darters have been observed only beneath the cover of rocks, except when moving between rocks. Young duskytails are highly territorial when cover rocks are scarce, but this behavior is greatly reduced when enough rocks of various sizes are available to provide cover for all individuals.

Duskytails are often found associated with detritus and are sometimes found on slightly silted substrates, but are rarely found in heavily silted areas, or in areas where silt does not fill or obscure the spaces between the cover rocks.

Distribution

Historically, this species has been collected from seven stream reaches; the duskytail darter is believed extirpated from Abrams Creek, Blount County, Tennessee, and South Fork Holston River, Sullivan County, Tennessee.

The duskytail darter is known from five reaches of the Tennessee and Cumberland River systems. The Little River population inhabits about 9 river mi (14.5 km). This population is potentially threatened by water withdrawal and increasing residential and commercial development in the watershed. In Citico Creek this species is affected by stream-side habitat destruction.

This darter inhabits about 17 river mi (27.4 km) of Copper Creek and may comprise the largest population. This population is currently threatened by siltation, riparian erosion, and agricultural pollution.

The duskytail darter has been taken from one site on the Big South Fork of the Cumberland River. This particular population is faced with the threat of runoff as a result of coal mine activities in the upper watershed above Big South Fork National Recreational Area.

In the Little River, the duskytail darter population has been documented from two localities that are about 9 river mi (14.5 km) apart. Despite yearly intensive sampling, there have been very few collections of the species from the upstream Little River localities since their discovery there in the 1970s. The relative abundance in the upper reaches is much less than at the lower site in the Little River. In the Little River, the stronghold for the species may be limited to a short river reach just upstream from the backwaters of the Fort Loudon Reservoir. Estimates were that this area was inhabited by more than 1,000 adult duskytail darters in the fall of 1993, but in other formerly occupied habitat, an extensive snorkel survey found no duskytails. The area was heavily silted, and extensive algal growth was noted in the rocky area normally inhabited by these darters. This degradation apparently resulted when flow was restricted by a logjam at a bridge: this allowed silt to settle in the slower current sections of the duskytail darter's preferred habitat.

Threats

Generally this species of Etheostoma is threatened by water quality degradation as a result of siltation and other pollution from poor land use practices, coal mining, and waste discharge.

The Tennessee and Cumberland Rivers are renowned as two of the most severely altered river-ine systems due to many anthropogenic activities. Most of the main stems of both rivers and many tributaries are impounded; impoundments usually alter downstream aquatic habitats. In addition, there has been a loss of the riverine habitat.

Siltation and toxic runoff have been the result of coal mining activities which unavoidably have adversely affected many reaches. Runoff from urban areas has also degraded water and substrate quality. The aquatic faunal diversity has declined due to this habitat destruction.

Due to the limited distribution of this species, a stochastic event such as an accidental toxic chemical spill could cause extirpation. As the populations are separated by impoundments, natural recolonization of an extirpated population would be virtually impossible.

Conservation and Recovery

The duskytail population in the Big South Fork of the Cumberland River is within the National Park Service's jurisdiction, and the populations in the Little River and Citico Creek occur within, but mostly below, lands controlled by the National Park Service and U.S. Forest Service, respectively. These federal agencies are aware of these populations and have taken proactive measures to protect them. Populations with a federal connection have greater opportunities for protection under existing laws than the population in Copper Creek, which is totally on private lands.

Apparently, the duskytail darter has been able to withstand some degree of habitat degradation. However, some habitat has been so severely altered that the species is extirpated or the population is reduced in size and vigor. Knowledge of the species' specific microhabitat requirements and the ecological associations for each population is needed in order to focus management and recovery efforts on the specific problems within the species' habitat.

Contacts

Regional Office of Endangered Species
U. S. Fish and Wildlife Service
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

Regional Office of Endangered Species
U. S. Fish and Wildlife Service
300 Westgate Center Dr.
Hadley, Massachusetts 01035
http://northeast.fws.gov/

References

U.S. Fish and Wildlife Service. April 27, 1993. "Determination of Endangered Status for the Duskytail Darter, Palezone Shiner and Pygmy Madtom." Federal Register 58(79):25758-25763.

U. S. Fish and Wildlife Service. March 30, 1994. "Recovery Plan for the Duskytail Darter." U.S. Fish and Wildlife Service, Atlanta, 25 pp.