|Listed||September 1, 1988|
|Description||Olive to gray darter with dark patches below and behind the eye.|
|Habitat||Deep, fast-moving water over boulder substrate.|
|Food||Probably immature aquatic insects.|
The boulder darter, Etheostoma wapiti, also known as the Elk River darter, is an olive to gray fish, reaching a maximum length of 3 in (7.6 cm). Females are generally lighter, but both sexes have dark patches below and behind the eye. The boulder darter lacks the red spots characteristic of closely related species. The species has also been classified in the genus Nothonotus.
Less than 50 specimens of the boulder darter have ever been collected. Because of this rarity, nothing is known of its life history or breeding biology. It is probably a sight feeder of immature aquatic insects.
The preferred habitat of the boulder darter is deep, fast-moving water over boulder and slab rock bottoms.
This darter has been found in the Elk River from Fayetteville (Lincoln County, Tennessee) downstream through Giles County into Limestone County, Alabama. Specimens have also been collected from three Elk River tributaries: Indian and Richland creeks (Giles County, Tennessee) and Shoal Creek (Lauderdale County, Alabama). Biologists believe that the species once inhabited the southern bend of the Tennessee River, near its confluence with the Elk River.
The boulder darter is now restricted to about 23 mi (43 km) of the Elk River (Giles County, Tennessee, and Limestone County, Alabama) and 2 mi (3 km) of Indian and Richland creeks (Giles County, Tennessee). Within this restricted range, the darter is further limited by its specific habitat requirements.
The spotty occurrence of the boulder darter in the Elk River results in part from the rarity of its preferred habitat. As its common name suggests, the boulder darter lives among boulders. However, it is not found among boulders anywhere in the river bed; the location of the boulders is important. The boulders must occur in water 2-4 ft (0.6-1.2 m) in depth. Also, the boulders must occur in flowing water that is not too swift, such as in riffles or rapids, and not too slow, as in slightly flowing pools.
Most of the Elk River between the reaches affected by impoundment consists of long, heavily silted pools that have little or no boulder substrate. The relatively few riffles and runs are predominately floored with gravel and rubble substrates. At two of the six sites that harbor boulder darters, the boulders are in fact parts from old collapsed structures, a stone bridge and a spillway dam. The survival of the bolder darter is amazing considering the rarity of its preferred habitat and the severe and chronic degradation of the Elk River.
Extirpation of the boulder darter from the upper Elk River in Tennessee was likely due to cold water releases from Tims Ford Reservoir. The loss of the Shoal Creek population and any Tennessee River populations resulted from water impoundments behind Wheeler and Wilson Dams.
Although no new dams are currently planned for the watershed, other factors, such as increased siltation, improper pesticide use, toxic chemical spills, and phosphate mining could further threaten the species in the limited habitat it now occupies.
Conservation and Recovery
Biologists have long recognized the critical importance of knowing the reproductive biology of any imperiled species, especially for developing conservation measures to protect and recover the species. Until recently, however, virtually nothing was known about the life history of the boulder darter. The first goal in researching the species was to observe its spawning behavior and to identify the area(s) of the river that served as spawning habitat. Unfortunately, observing boulder darter spawning behavior was not possible in the Elk River because of the water's consistent turbidity. Further, the river below Tims Ford Dam is subject to significant water level fluctuations resulting from power generation at the dam. In order to overcome the obstacles to studying the darter in its natural environment, ten darters were captured, transported to Gainesville, Florida, and placed in an artificial stream.
The artificial stream is a 4 by 8 ft (1.2 by 2.4 m) plexiglass aquarium generated by an electric trolling motor. Researchers mimicked important aspects of the boulder darter's habitat in the artificial stream, notably flow, temperature, photoperiod, and substrate composition. The boulder darters spawned in May and June 1991, yielding the first observations of reproduction for this endangered species. What was learned in this short period provided important insight into the inherent frailties of this darter at the critical point of creating the next generation.
Regional Office of Endangered Species
U.S. Fish and Wildlife Service
1875 Century Blvd., Ste. 200
Atlanta, Georgia 30345
O'Bara, C. J., and D. A. Etnier. 1987. "Status Survey of the Boulder Darter." U.S. Fish and Wildlife Service, Asheville.
U. S. Fish and Wildlife Service. 1988. "Determination of Endangered Status for the Boulder Darter." Federal Register 53(170): 33996-33998.
U. S. Fish and Wildlife Service. 1989. "Boulder Darter Recovery Plan." U.S. Fish and Wildlife Service, Atlanta.