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INTRODUCED FISHES OF THE LOWER COLORADO 79 4TRODUCED ') RIVER, DES 1 ,wer Colorado River ,utochthonous detri- nd crayfish eaten by the water. Threadfin is food, were major modified channels in ,f aquatic habitats in ,uppressed, and this der essentially com- native fishes, highly rated from the main- necies, is becoming ,4--. from the reach :ry, 20 of which are I Most published n 1931, Miller 1961, 11 discussions of the Kimsey 1958), 1inckley 1971 a), and 11 %d observations on tuyle 1976). Part of or conducted from 1, -1 n the fish fauna. n outline of trophic -Is of striped bass, and below by the r between Nevada 'liuch of the study southern extreme earn from the Gulf 'ering this 453-km maintained below except in periods 1 I of unusually high runoff (Brown, Carmony, and Turner 1978). The latter is also impounded and sometimes ceases to flow at its mouth. Local precipitation seldom exceeds 12 cm per year, summer air temperatures often rise to greater than 40°C, and winter temperatures rarely drop below freezing for more than a few hours. I_NV I _ '-7- NEVADA UT Lake ` ! \ Mohave I , CAS --r- \ Davis Dam AZ \ ?,- Needles AR IZONA 0 o Topock Lake Havasu ' CALIFORNIA Parker Dam l Parker N B I yt heo Palo Verde Diversion Imperial -./-- Laguna Dam Dam & Reservo i r Mora I es Dam uma km MEXICO 0 40 80 s 1 FIGURE 1. Map of the lowermost Colorado River, southwestern United States, with some place names mentioned in text. Terrain along the river ranges from precipitous cliffs, where the stream has eroded through mountain ranges, to low, broad floodplains. Slopes and terraces are stony along mountain fronts. Lower terraces and floodplains are composed of fine sands and silts. The sparse natural vegetation of the region is classified as Sonoran desertscrub (lower Colorado River subdivision; Brown and Lowe 1980). Plant communities,