7848 - Laserfiche WebLink

Home Browse Search

this reason, the minimum flow recommendation in this report is primarily for sub- adult and adult Colorado squawfish passage only. Until information can be obtained for razorback sucker in the reach, it is assumed that flows recommended suitable for Colorado squawfish will also benefit razorback sucker. RESULTS AND DISCUSSION Fish Captures Colorado squawfish Past Sanpling. For the 11 years analyzed between 1979 and 1995, July had the highest catch rate for Colorado squawfish collected in the plunge pool (7.1 F/h) and 2.2-mile reach (3.3 F/h; Appendix; Table D.2.). August had the second highest catch rate for Colorado squawfish collected in the plunge pool (2.4 F/h; Appendix; Table D.2). The lowest flow months in the 2.3-mile reach occur in July and August. There were 111 days when flow was less than 300 cfs in this reach during July and August from 1979-1995. The higher catch rates and densities reported for these two months may be related to spawning in the reach or to increased capture vulnerability during low-flow periods. In other words, Colorado squawfish may be easier to catch during low-flow conditions compared to high-flow stages. Instances have occurred during low-flow periods of Colorado squawfish occupying the plunge pool. In 1981, there were 93 days when flows were less than 300 cfs in the reach, extending from 20 March to 30 August. In 1981, when flow was 192 cfs, a large adult Colorado squawfish (TL=827 mm) was captured in the plunge pool (Appendix; Table D.1.). Between 14 and 20 May, there were six days when the flow was less than 300 cfs, the lowest being 69 cfs on 15 May. On 12 August 1988, a radiotagged Colorado squawfish (TL=750, radio frequency=40.470) was located in the plunge pool when the flow was 23 cfs (Appendix; Table D.3.). The plunge pool was probably isolated from downstream reaches of the Lower Gunnison River at that time. This fish was probably "held hostage" in the plunge pool for 14 more days until 27 August when the flow increased to 238 cfs and the plunge pool was hydrologically reconnected to the downstream reach. It is uncertain when this fish entered the pool or how long it had been in the plunge pool prior to 12 August because radio contact had not been made with this fish during July and August and it is unknown if and when the plunge pool was hydrologically isolated from the downstream reach. Prior to 12 August, the flow had been less than 200 cfs for the first 11 days of August. The flow between the 15 and 31 July had been less than 100 cfs; 12 of those 17 days the flow ceased in the reach. The plunge pool provides deep-water habitat even during low-flow periods. A depth profile of the plunge pool indicates that a mean and maximum depth of 6.7 and 9.7 feet, respectively, is available at 100 cfs. During low-flow periods the plunge pool may become isolated from the downstream reach and if Colorado squawfish do not travel downstream to "wait out" the low-flow period, they may become stranded in.the plunge pool. During such times, Colorado squawfish are confined with other native and nonnative fishes and are not free to utilize the resources of the entire reach. The plunge pool provides a temporary refuge for 12