Watercress Darter

Etheostoma nuchale

Description

The watercress darter, Etheostoma nuchale, is a small, robust fish growing to a maximum length of 2 in (5 cm). Breeding males are blue above, red-orange below, and have blue and red-orange fins.

The spiny dorsal fin has an outer margin of blue followed by bands of red, blue, and red. This pattern is well-developed in breeding males, faint in females. The soft dorsal fin of males displays the same pattern, while the anal, basal portion of the caudal, and the paired fins are blue. In females, the soft dorsal, anal, caudal, and paired fins are speckled with small brown spots.

Behavior

This darter feeds on aquatic insects, crustaceans, and snails. Little is known about its behavior.

Males exhibit courtship behavior to all females encountered, and non-receptive females leave the area when approached by males. The courting male stays close to the receptive female and may rest his head on her back or neck, touch sides, or display his fins. Other males in the area try to displace the courting male. Larger males are generally successful. Eggs are deposited in submerged vegetation.

Habitat

The watercress darter inhabits deep, slow-moving backwaters of spring outflows. These areas support dense aquatic vegetation and particularly watercress (Nasturtium officinale ), which attracts a large community of aquatic insects, the darter's principal food.

Distribution

The species was discovered in 1964 at Glenn Springs near Bessemer, Alabama. Because of its recent discovery, the historic range of the watercress darter is unknown.

The watercress darter has been found in three springs in Jefferson County, Alabama: Glenn Springs and Thomas' Spring in Bessemer, and Roe-buck Springs in Birmingham. The species also occurs in Tapawingo Springs in Jefferson County, where it was successfully transplanted in 1988. Reproduction has since taken place, indicating that this new population introduction was a success. A similar transplantation was undertaken at Avon-dale Springs, also in Jefferson County, although no evidence of reproduction had been found by 1993. While not conclusive, limited population survey results indicate an apparent downward trend for all of the naturally occurring populations, though the transplanted population seems to be doing well.

Threats

The greatest threats to this species appear to be habitat alteration and pollution. The growth of the Birmingham-Bessemer metropolitan area has resulted in extensive residential construction (notably apartment complexes and shopping malls) and the paving of large areas for streets and parking lots. The springs supporting the watercress darter depend on rainfall for recharging, much of which has now been diverted into drains and gutters. As a result, water levels in the springs tend to fluctuate widely.

Roebuck Spring, which had been a source for local drinking water, was condemned in the 1970s because of a level of bacteria too numerous to count. This contamination was possibly caused by seepage from nearby residential septic tanks. Darters in the spring suffer from gas bubble disease, which is caused by high levels of sewage-derived nitrogen in the water. Nitrogen gas builds up in the body of the fish, eventually killing it. This contamination of the Roebuck Springs habitat basin and its run has been identified along with an alarming decline in the watercress darter at the site. Concerned by the decline, in 1991 the U. S. Fish and Wildlife Service (FWS) conducted a contaminant investigation, and analysis of sediment and snail samples reported high levels of polycyclic aromatic hydrocarbons, a highly toxic substance to the fish.

The introduction of alien fish to the habitat has also affected the watercress darter populations. Grass carp were introduced into Thomas' Spring and by 1977 had removed all vegetation up to the shoreline and eliminated the natural darter population.

Conservation and Recovery

In 1980 the FWS purchased Thomas' Spring and 7 acres (2.8 hectares) of surrounding land for the Watercress Darter National Wildlife Refuge, which is administered as part of the Wheeler National Wildlife Refuge. The grass carp were removed, the spring revegetated, and the watercress darter reintroduced from the Glenn Springs population. An additional pond has been built at the refuge and three small dams at Glenn Springs should restore the darter's habitat there. The owner of Glenn Springs signed an agreement allowing habitat management and conservation, and in 1988, 100 water-cress darters were transplanted from Thomas' Spring into the newly constructed pond.

Successful recovery efforts include the January 1988 transplantation of 200 fish to Tapawingo Springs and Avondale Springs, both in Jefferson County. Reproduction has since occurred repeatedly in Tapawingo Springs, although by 1993, no watercress darters had been collected at Avondale Springs (collecting conditions are difficult at that site, however).

The 1993 recovery plan revision for the species notes that recovery goals are first reclassification (from Endangered to Threatened) and then delisting altogether. The species would be considered for reclassification when long-term protection has been achieved for the three known naturally occurring populations and one of the additional populations within the historic range, and when there are five years of data indicating that a minimum of four populations are viable. To delist the species, the FWS requires five years of data documenting the existence of six viable populations (each in separate discrete recharge areas) and the proven long-term protection of the discrete recharge area for each viable population.

To achieve these goals, the 1993 plan calls for a number of activities, including the implementation of actions to determine the genetic structure of the various populations; the correction of water quality and quantity problems; the transplantation of watercress darters to additional sites, augmenting the naturally occurring populations and protecting genetic diversity; and determination of the discrete recharge area for each viable population. The plan also calls for the achievement of long-term protection of the recharge area and the immediate habitat from threats to six viable populations.

Contact

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

References

Howell, W. M., and R. D. Caldwell. 1965. "Etheostoma (Oligocephalus) nuchale, a New Darter from a Limestone Spring in Alabama." Tulane Studies in Zoology 12 (4):101-108.

U.S. Fish and Wildlife Service. 1984. "Recovery Plan for the Watercress Darter (Etheostoma nuchale )." U.S. Fish and Wildlife Service, Atlanta.

U.S. Fish and Wildlife Service. 1993. "Revised Recovery Plan for the Watercress Darter (Etheostoma nuchale )." U.S. Fish and Wildlife Service, Atlanta.