The Nonnative Iowa Darter (Etheostoma Exile) Established in the Yampa River, Colorado, And Green River, Utah (Notes) (Report‪)‬

Native distribution of the Iowa darter (Etheostoma exile) extends north to central Canada, east to New York, south to central Illinois, and the species is particularly common in western Great Lakes drainages and Iowa (Scott and Crossman, 1973; Lee and Gilbert, 1978). Western populations are distributed patchily in Colorado, Wyoming, Montana, and Alberta, perhaps as glacial relicts. Native in Colorado only in the South Platte River drainage, the Iowa darter occurs primarily in small, cool, and clear streams or vegetated ponds in the Rocky Mountain foothills or plains, habitat similar to that occupied in the center of its range (Ellis, 1914; Hendricks, 1950; Li, 1968; Baxter and Simon, 1970; Scott and Crossman, 1973; Lee and Gilbert, 1978; Becker, 1983; Propst and Carlson, 1986; Bestgen, 1989). Native populations of the Iowa darter in Colorado are listed as a Species of Special Concern by the Colorado Division of Wildlife. Iowa darters have been collected in Shadow Mountain Reservoir in the headwaters of the Colorado River, Colorado, where they likely were introduced via bait-bucket transfer (Propst, 1982; Woodling, 1985). Other records of the Iowa darter from the Colorado River Basin in the Dolores and San Juan rivers (Beckman, 1974; Lee and Gilbert, 1978; the latter may be the Etheostoma recorded from the Animas River by Sublette et al., 1990) are not supported by specimens and it likely is not established there, based on absence of more recent specimens (Woodling, 1985). Historical and recent sampling in the Yampa River, including that conducted within our study areas as recently as 2001 and with comparable sampling gear, failed to detect the Iowa darter (Holden and Stalnaker, 1975; R. Anderson, pers. comm.) The Yampa River is a tributary to the Green River, and the Green River is the largest tributary of the Colorado River in the Upper Colorado River Basin. Sampling of the Yampa River occurred in three areas. The most upstream reach, Little Yampa Canyon (river km 161-200, just downstream of Craig, Colorado), and the intermediate reach, Lily Park (river km 80-89), were sampled with an electric seine (10 m long, 2 kW generator). The most downstream site on Yampa River at Echo Park (river km 1) was just upstream of the confluence of the Green River and sampling was conducted with drift nets (4 m long, 0.5 [m.sup.2], 560-[micro]m mesh). The sampling site on the Green River, 68 river km downstream of the confluence of Yampa River near Jensen, Utah (backwater of Cliff Creek confluence, river km 487 of Green River, and other backwaters downstream of there), was with light traps (quatrefoil design, slits were 4 or 6 mm wide) set overnight. Results reported here are from portions of several studies with differing research objectives, which is why different types of gear were used at most locations.