Niangua Darter

Etheostoma nianguae

Description

The slender Niangua darter, Etheostoma nianguae, is a large, long (3-4 in, 7.5-10 cm) slender fish with a long head that tapers into a slender, pointed snout. Its basic color is yellowish-olive with seven or eight dark saddle bars on its back, and orange spots scattered on the upper sides. A series of U-shaped greenish blotches alternate with orange bars along the mid-side, and two small jet black spots at the base of the caudal fin. Breeding males exhibit an orange-red belly and a series of iridescent blue-green bars along the sides.

Behavior

The Niangua darter spawns in spring in swift currents over gravel bottoms. Breeding males (both males and females are sexually mature at one year of age) precede females to the spawning riffles to await their arrival. Encounters between the mating fish begin with head-bobbing by the female, followed by threat displays that include erection of the dorsal fin; encounters between males include a change in color patterns that heightens the contrast between the light background and darker markings, especially the saddle bar behind the pectoral fin.Spawning occurs as the female lies buried in the gravel where she deposits eggs, with the male above. Most Niangua darters live to two years of age, although some survive to four.

The Niangua darter feeds almost exclusively on aquatic insects. Altough nine species of darters occur in association with the Niangua darter, competition for food is probably minimized because of different feeding strategies. The Niangua darter obtains its food by probing crevices with its slender snout.

Habitat

The species inhabits clear, medium-sized streams that run off hilly areas underlain by chert and dolomite. It is usually found in the margins of shallow pools with silt-free, gravel, or rocky bottoms, and occasionally boulders or bedrock. The greatest concentration of fish occurred in stream areas that had thick growths of water willow although it does not seem to have any dependence upon this vegetation.

Distribution

The Niangua darter is part of a diverse fish fauna, encompassing 107 species in the Osage basin. It is known only from a few tributaries of the Osage River in Missouri, where eight populations along 128 mi (205 km) of the river basin were reported in the early 1970s. These populations were in the Maries River and Lower Maries Creek (Osage County); Big Tavern Creek and upper Little Tavern Creek, Barren Fork, and Brushy Fork (Miller County); Niangua River and Greasy Creek (Dallas County); Little Niangua River, Starks Creek, Thomas Creek, and Cahoochie Creek (Camden, Hickory, and Dallas counties); Little Pomme de Terre River (Benton County); Pomme de Terre River (Green and Webster counties); Brush Creek (Cedar and St. Clair counties); and the North Dry Sac River (Polk County).

The Niangua darter population is believed to have declined at most Missouri sites in recent years. An intensive on-site habitat analysis concluded that the species is rare, localized in occurrence, and vulnerable to extinction.

Threats

Construction of the Truman Reservoir formed a barrier to the Niangua darter's movement between tributary streams, fragmenting its range. Migration between these tributary streams is considered important to the long-term survival of the species.

Highway and bridge construction projects frequently straighten and widen stream channels, and landowners channel streams to control local flooding. These practices have led to pervasive sedimentation and silt pollution throughout this darter's range. In addition to stream channelization, the practice of removing woody vegetation from stream banks causes increased erosion, changes in the character of the stream substrate, elimination of pools, and the alteration of stream flow, all of which seriously disrupt the stream ecosystem.

Spotted bass and rock bass were introduced into the Osage basin before 1940 and are now widely distributed. Diffusion of seven species of predatory fishes from reservoirs into tributary streams inhabited by the Niangua darter could further reduce the population.

Conservation and Recovery

Habitat considered critical for the darter's survival has been designated for portions of Camden, Cedar, Dallas, Greene, Hickory, Miller, and St. Clair Counties, Missouri. It encompasses some 90 mi (145 km) of inhabited stream and a 50-ft (15-m) stream-bank buffer zone.

The Recovery Plan calls for the long-term protection of riparian habitat, including land protection and aquisition; reducing adversely agricultural practices and stream bank modification; controlling the use of pesticides and herbicides; preventing channelization; eliminating passage barriers or providing fish passage devices; controlling the infiltration of predator fish; and reintroducing wild and captive fish to the habitat.

Contact

Regional Office of Endangered Species
U.S. Fish and Wildlife Service
Federal Building
Fort Snelling, Minnesota 55111
http://midwest.fws.gov/

References

Missouri Department of Conservation. 1974. "Rare and Endangered Species of Missouri." Pamphlet. Missouri Department of Conservation, Jefferson City.

Pflieger, W. L. 1971. "A Distributional Study of Missouri Fishes." Museum of Natural History, University of Kansas Publications 20(3):229-570.

Pflieger, W. L. 1975. "The Fishes of Missouri." Missouri Department of Conservation, Jefferson City.

Pflieger, W. L. 1978. "Distribution, Status, and Life History of the Niangua Darter, Etheostoma nianguae." Aquatic Series No. 16. Missouri Department of Conservation, Jefferson City.

U.S. Fish and Wildlife Service. 1989. "Recovery Plan for the Niangua Darter." U.S. Fish and Wildlife Service, Twin Cities.