WSP05364 - Laserfiche WebLink

Home Browse Search

. . 8 less than 1.5 feet in depth over a silt substrate. Juvenile Colorado squawfish habitat preferences are similar to the YOY fish, but the juveniles appear to be mobile and adaptable to lotic conditions away from the sheltered environment provided by backwaters. Information on radio-tagged Colorado squawfish that have been observed during fall suggests that fish seek out deepwater areas in the Colorado River (Miller, et al., 1983), as do many other riverine species. River pools and other deepwater areas, especially in upstream reaches, are probably important wi nter habitats for Colorado squawfi sh. In laboratory studies, the preferred total dissolved solids (TDS) for juvenile Colorado squawfish was determined to be between 600 and 1,000 milligrams per liter (mg/l); concentrations greater than 4,000 mg/l were completely avoided. TDS concentrations in the Colorado River seldom exceed 2,000 mg/l (Miller, et a 1 ., 1982). Very little information is available on the influence of turbidity on the endangered Colorado River fishes. It is assumed, however, that turbidity is important, particularly as it affects the interaction between introduced fishes and the endemic Colorado River fishes. Since these endemic fishes have evolved under natural conditions of high turbidity, it is assumed that the retention of these highly turbid conditions is an 'important factor for these endangered. fishes. Reduction of turbidity may enable introduced species to gain a competitive edge which could further contribute to the decline of the endangered Colorado River fishes. Area of Immediate Impact The reach of currently known occupied habitat that will receive the most impact due to upstream water withdrawals related to the proposed Ruedi II water sale is the main stem Colorado River between Palisade, Colorado (RM 185), and the confluence with the Gunnison River (RM 170). This reach of the Colorado River is regulated by two large agricultural diversion structures and one dam barrier located in nearby upstream areas. The first of these water diversions is located immediately upstream from RM 185. Known as the Grand Valley Irrigation Company diversion, this structure diverts water from the Colorado River at rates up to about 640 CFS during the growing season. (April to October) and smaller amounts during the winter for stock watering. The 6rand Valley Irrigation Company has been diverting since 1883. Colorado squawfish are known to occur in the river immediately downstream from this diversion, and it is thought that adult squawfish are able to successfully swim over this low-head structure during all but extremely low-flow stages. Until the 1980's, cracks and seepage areas in the diversion dam provided some flow in the Colorado River below the structure, even during extreme low-flow conditions, but recent repair has made it virtually leak-proof (Henderson, 1985).