Percina evides (Jordan and Copeland, 1877)
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Basis for Listing
In Minnesota, the Gilt Darter (Percina evides) occurs only in the St. Croix, Snake, and Kettle rivers and lower reaches of their large tributaries. Its limited distribution makes it vulnerable to decline and possibly extirpation through catastrophic events. Although the closest stable populations are in the Chippewa and lower Black rivers of Wisconsin, the Mississippi River does not offer an avenue for recolonization. The Minnesota-Wisconsin St. Croix River population is disjunct from those of the Ozarks and the Tennessee Uplands. (Hatch et al. in preparation). Genetic analysis determined populations across the species’ range are comprised of one eastern and two western clades. The Minnesota and Wisconsin populations belong to a western clade and the data suggests these be recognized as a new species (Near and Page 1999). Regionally, the Gilt Darter is listed threatened in Wisconsin. Elsewhere across its range it has greatly declined or is presumed extirpated. It was listed as a species of special concern in 1996.
The Gilt Darter is a robust, stout darter. Seven saddle bands straddle the dorsal ridge, joining dark blotches midside. In breeding males, the bands turn an iridescent blue-green; while areas between the blotches as well as the head, spinous dorsal fin, and ventral portions of the body turn brilliant yellow and orange. At the height of the breeding season, a blue-black pigment accumulates in the breast, pelvic, and spinous dorsal fins and at the base of the anal fin. Adults average 7.9 cm (3.1 in.) in total length (Becker 1983).
The species is very similar in appearance to the Logperch (P. caprodes), Blackside Darter (P. maculata), Slenderhead Darter (P. phoxocephala), and River Darter (P. shumardi) (Lyons et al. 2012). Gilt Darters can be distinguished from the other species by a body pattern of 5-8 thick, squarish, vertical bars or blotches extending onto the back and solid pigment in the first dorsal, which is orangish in live specimens, except for a thin clear or white edge.
The Gilt Darter occurs in riffles of medium- to large-sized streams, with strong to moderate currents, and is generally most abundant in the deeper portions of its habitat. The species also requires streams with relatively strong, year-round flow and clean gravel and cobble substrates for spawning (Hatch et al. in preparation).
Biology / Life History
In summer, the Gilt Darter is found most frequently in rubble riffles and cobble or boulder raceways, where currents are moderate to swift. It rarely occurs in pools or in association with rooted aquatic vegetation. In the fall, it moves to deep chutes of rubble and boulder riffles, where it over-winters. Mature individuals return to shallower areas to spawn in mid-May to late July. Males establish territories around cobble or boulder stones. In the Sunrise River, specimens have been observed feeding during the day. The species' diet includes mayfly, caddisfly, and diptera larvae (Hatch et al. in preparation).
Conservation / Management
The Gilt Darter is sensitive to sediment loading and probably organic loading from sewage effluents, making them important indicators of degraded water quality. In spawning habitats, high levels of suspended sediments can smother eggs and likely have an adverse effect on the species’ ability to feed. Their distribution has become fragmented over the past century. In Minnesota, the species requires a combination of habitat characteristics (low siltation, strong, year-round flow, clean substrate for spawning) that occurs only in the St. Croix River drainage. Silting of spawning habitats has likely prevented Gilt Darter populations from becoming established in streams of central and southern Minnesota (Hatch et al. in preparation). Additional research needs in Minnesota include identification of habitat guilds and population stressors.
Conservation Efforts in Minnesota
Recent DNR and Minnesota Pollution Control Agency surveys extended the species range further upstream in the Kettle and Snake rivers and indicates the population is stable throughout its historical distribution (Hatch el al. in preparation; Proulx 2005). The designation of the St. Croix as a National Scenic Riverway protects much of the species mainstem habitats. The recent inception of Minnesota’s Clean Water Legacy Program will eventually yield benefits to Gilt Darter habitats on tributaries through nutrient and sediment load reductions by establishing buffer strips for riparian protection.