|Listed||December 27, 1993|
|Description||Small bright to dullish blue darter.|
|Habitat||Slow to moderate waters flowing over sand and fine gravel substrates.|
|Threats||Siltation and pollutants from coal mining, gravel mining, poor land use practices, and waste discharges.|
The bluemask darter is a small, slender fish that reaches a maximum size of 1.9 in (4.8 cm). Females and nonbreeding males are straw-yellow to tan. Along the sides there are seven to nine quadrate blotches formed by dark X-markings and faint blue pigment. Between the blotches and extending dor-sally there are many small orange X-markings and spots. Dorsolaterally there are also many small brown markings. On the dorsum there are six dark brown saddles. The face and underside of the head are white to dusky, and there is blue pigment on the suborbital bar and operculum. The cheeks are fully scaled, and the lateral line is usually complete. The first dorsal fin contains a narrow dusky marginal band, a red-orange medial band, a dusky submedial band (males only), and a clear basal band. The second dorsal and caudal fins are mostly clear.
Breeding males are generally dusky with seven to nine bright cobalt blue bars on the side of the body. Between the bars, orange spots coalesce to form conspicuous splotches. Bright cobalt blue continuously covers the face, underside of the head, and branchiostegal membranes. The first dorsal fin contains a narrow gray to black marginal band, a bright red-orange medial band, a wide black submedial band, and a mostly clear basal band with black pigment in the posterior portions of the membranes. The second dorsal, caudal, anal, and pelvic fins are dusky gray to black.
The bluemask darter can be distinguished from Etheostoma stigmaeum and the blueside darter (E. jessiae) by: fully scaled cheeks; lateral line usually complete; premaxillary frenum absent; breeding males with bright cobalt blue pigment continuously covering the lower face and underside of the head; breeding males with soft dorsal and anal fins with no orange spots on rays or blue pigment in membranes; and palatine teeth absent.
The bluemask darter occupies areas with slow to moderate flow over sand and fine gravel substrates. This type of habitat is seemingly limited within the Caney Fork River system of central Tennessee.
Bluemask darters have been collected in slow to moderate current over clean sand and fine gravel at depths of 4-20 in (10.2-50.8 cm), typically just downstream of riffles or along the margins of pools and runs. They inhabit the lower free-flowing reaches of streams on the Highland Rim with substrates of limestone or chert bedrock, coarse chert gravel, and sand. Spawning males were collected from the Collins River in April 1991 over sand and gravel in moderately flowing runs. The closely related E. stigmaeum, which shares an affinity for sand and gravel substrates, spawns in early spring by burying eggs in gravel. The upper reaches of all four streams that support the bluemask darter flow underground during summer, with little to no surface flow. This limits perennial habitat for the species to the lower stream reaches.
Historically this species was known from five rivers in the Caney Fork River system. Presently this darter is known from only four rivers in Van Buren, Warren, Grundy, and White Counties. The blue-mask darter is thought to inhabit about 700 ft (213.4 m) of Cane Creek; 23 mi (37 km) of the Collins River; 2.7 mi (4.3 km) of the Rocky River; and 1.1 mi (1.8 km) of the upper Caney Fork River. The species may also seasonally occur in the 1.9-mi (301-km) reservoir fluctuation zone in the upper Caney Fork River and the 0.8-mi (1.3-km) fluctuation zone in Cane Creek. Eight specimens were collected there on two occasions in the spring of 1990. Eight individuals were collected from the free-flowing portion of Cane Creek, just upstream of the Great Falls Reservoir in 1991.
The bluemask darter was collected at two localities in the Caney Fork River in the lower 1.1 river mi (1.8 km) above the Great Falls Reservoir. Twelve specimens were collected in relatively high flow along the margin of the stream over cobble and sparse gravel at a site 1.6 mi (2.6 km) east-southeast of Dodson, White County, during April 1991. On a return trip to the site in August 1991, the channel was completely dry, with the exception of widely scattered pools with substrates of large round boulders.
In the Caney Fork River, 14 bluemask darters were observed in a large pool over silty sand, detritus, and occasional small cobble in a large spring-fed isolated pool a short distance upstream of the site in waters temperature of 75-78°F (23.9-25.6°C). Large pools like this one, which are widely scattered, may be critical in sustaining populations through low flow periods. Because the perennial flow appears to be limited to the lower river, and because summer hold-over pools are widely scattered, this bluemask darter population must be extremely small and thus vulnerable to disturbance or habitat alteration.
The bluemask darter's distribution has been reduced by such factors as impoundments, water withdrawal, and the general deterioration of water quality resulting from siltation and pollutants contributed by coal mining, gravel mining, poor land use practices and waste discharges.
Because the existing bluemask darter populations inhabit only short stream reaches, they are vulnerable to extirpation from stochastic events, such as accidental toxic chemical spills. The valley along the Collins River is used extensively for commercial plant nurseries; this increases the chances of a toxic agricultural chemical spill and the buildup of contaminants in the stream sediment that could impact this population. Additionally, all existing bluemask darter populations are now isolated by the Great Falls Reservoir. Because the Cane Creek and upper Caney Fork River populations are extremely small and the Great Falls Reservoir presumably restricts gene flow among populations, the long-term genetic viability of all the populations is questionable.
Conservation and Recovery
U. S. Fish and Wildlife Service (FWS), in cooperation with willing landowners, has begun to implement programs to restore riparian habitat, fence cattle from stream reaches, develop alternative water supplies for cattle, and control agricultural run-off in other streams in the southeastern United States. These programs, which are designed to benefit both the landowner and the resource, help minimize soil erosion and enhance bluemask darter habitat.
Although the bluemask darter has been able to withstand some degree of habitat degradation, some of its habitat has been so severely altered that the species was extirpated from one stream, and other population segments have been reduced in size and vigor. The FWS is conducting research to determine the species' specific microhabitat requirements and ecological associations. Specific components of the species' habitat may be unknown, and certain activities in the watershed may be adversely impacting the species. Habitat improvement programs may be needed to increase spawning success. Structures may be needed to provide cover and summer pool habitat and to stabilize the stream bank and streambed. Cooperative projects with landowners to provide alternative water sources may be needed to help minimize the impacts of water withdrawal projects.
The exact historic range of the bluemask darter is unknown. However, based on historic collection records, the species has been taken from only five rivers and creeks. The species is extirpated from the Calfkiller River, and because of significant habitat deterioration, including impoundments, siltation, and water quality degradation, it may not be possible to reintroduce the fish into this system. However, further study is needed to determine when water quality and physical habitat is suitable for reintroductions. Other streams may exist within the species' probable historic range that may be suitable for reintroduction, including the Barrens Fork River or lower reaches of Charles Creek or Mountain Creek in the Collins River system. If such streams exist, they might have potential for reintroduction success.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
Cookeville Ecological Services Field Office
U. S. Fish and Wildlife Service
446 Neal St.
Cookeville, Tennessee 38501-4027
Telephone: (931) 528-6481
Fax: (931) 528-7075
U. S. Fish and Wildlife Service. 27 December 1993. "Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Relict Darter and Bluemask (=Jewel) Darter." Federal Register 58 (246):68480-68486.
U. S. Fish and Wildlife Service. 25 July 1997. "Recovery Plan for Bluemask (=Jewel) Darter," U. S. Fish and Wildlife Service, Atlanta. 20 pp.