Boulder darter  (Etheostoma wapiti)

Classified as Vulnerable (VU) on the IUCN Red List (1).

Inhabiting fast-flowing rocky rivers, the boulder darter dashes between the sanctuary of large stones, a behaviour that is common to all darters and the origin of their common name (2) (3). Adapted to a bottom-dwelling lifestyle, the body is deep and slender with two separate dorsal fins, but unlike other teleosts, the boulder darter lacks a swim bladder, a gas filled sac typically used to regulate buoyancy (3). The male is an olive to grey colour and lacks red spotting, a common feature amongst other, related darter species. Both the male and female have a distinctive grey to black bar and spot behind the eye, but the female is slightly lighter in colour (4).

The boulder darter is found in the Elk River, and two of its tributaries, in the states of Alabama and Tennessee in the United States (2). In 2005, the boulder darter was reintroduced into Shoal Creek near Iron City in Tennessee (5) (6).

The boulder darter typically inhabits fast-flowing, small to mid-sized rivers, with boulder or slab rock substrate, in water over 60 centimetres depth (2) (5).

A rare and little-studied species, much of the boulder darter’s biology is, as yet, unknown. However, most darters are bottom-dwelling, diurnal fish that use sight to forage for immature insects, such as mayflies and stoneflies (4). These fish typically spawn between late May and early August, coinciding with a rise in water temperature to 18 to 23 degrees Celsius (2). The female boulder darter lays the fertilised eggs in a wedge-shaped cavity amongst large rocks in moderate to fast-flowing rivers. Once hatched, the juvenile fish alternate between resting on the bottom of the river bed and swimming, all the while feeding from an attached yolk sac. They will later become fully pelagic and will feed at the top of the water column on a variety of plankton (6). 

The boulder darter has been the unfortunate victim of habitat loss and degradation. Already confined to a specific and relatively rare habitat, the boulder darter was removed from the upper Elk River due to cold water release from the Tims Ford Reservoir. The construction of the Wilson Dam and resulting flooding also removed the species from Shoal Creek. Within its present range, the boulder darter is threatened by changes in land use causing increased sedimentation in the water, and pollution from chemical spills and improper pesticide use (2). The species restricted range and rarity also makes it vulnerable to the loss of genetic diversity, decreasing its ability to adapt to environmental changes (6).    

Owing to its rarity and habitat specificity, the boulder darter was listed as an Endangered Species on the U.S. Endangered Species Act in 1988. This led to the development of a detailed recovery plan outlining a programme of conservation for the species (2) (4). To date, studies into the species habitat requirements have been conducted as well as efforts to improve the prevalence of the species spawning habitat, including the placing of 3.5 tons of limestone slab into the Elk River in 2000. In addition, Conservation Fisheries have successfully released captive-bred fish into Shoal Creek (6) (7).

View information on this species at the UNEP World Conservation Monitoring Centre.

For more information on the boulder darter, see:

• U.S Fish and Wildlife Service Species Account:
  http://www.fws.gov/ecos/ajax/docs/life_histories/E05P.html