9302 - Laserfiche WebLink

Home Browse Search

provide significant inputs of nutrients and organic matter that comprise the energy base for fishes and other organisms. Despite the relatively large size of the basin, it supported a relatively depauperate native fish fauna that consisted of only about 54 forms representing 36 species (Table 1; Carlson and Muth 1989). Of these, 3 are marine species and at least 2 forms are extinct. In contrast, the nearby Missouri River basin, which drains about 529,000 mil, contains more than 150 fish species (Pflieger 1975). Many of the Colorado River fishes had very restricted distributions historically: six were found only in the upper basin, 24 ~ were found only in the lower basin, and only 8 were widely `~ distributed. The fauna can be divided into three separate fish communities: (1) fishes inhabiting high or intermediate elevations and which are represented or have closely allied forms in adjacent drainages, (2) endemic species of small streams at low to intermediate elevations, and (3) big river fishes, commonly called the Colorado River fishes, which are mainly endemic inhabitants of mainstream rivers (Minckley et al. 1986). The native big river fishes consisted of cyprinids (minnows) and catostomids (suckers) that were widely distributed in main channel habitats of the historic Colorado River basin (Jordan and Evermann 1896). The native fishes evolved over a long period of geographic isolation in the extreme climatic conditions of the historic Colorado River basin (Miller 1959, 1961; Molles 1980). The native fishes were adapted to the historical river system with its highly seasonal variations in flow and habitat availability. These fishes are considered to be generalists rather than 2