7422 - Laserfiche WebLink

Home Browse Search

. DRAfT . (Figure 9), and one in the lower region near Baeser Bend at RM 270.7 (Figure 10). Movement by the three razorbacks at Echo Park is largely attributed to changing water levels. OVer a period of 6 hours, the river rose by 2 vertical feet and inundated much area that was formerly exposed. All three razorbacks responded by moving from positions close to mid channel to positions closer to shore. It is believed that increasing velocities forced the fish to move from an eddy to a slackwater habitat. All three fish consistently located water depths of 3-4 feet and 0.6 velocities of less than 0.6 fps. These razorbacks showed an affinity for a certain combination of water conditions, that appear to be driven by low velocity, within certain minimum depths. . . Movement by razorback GR6108 (Figure 9) was belei ved to be in response to changing flows over a 24-hour period. Gross movement by this fish over the observation period was 90 m and net movement was 80 m, indicating that the favorite spots selected by the fish did not maintain satisfactory habitat characteristics. . In the case of razorback OR3257 (Figure 10), gross movement over a 24-hour period was 103 m while net movement was 20 m. A change of 2 inches in vertical water level occurred during this time. This fish occupied three favorite spots for periods of 15, 4, and 5 hours. It is difficult to attribute local movement by this fish to changing water level, but it is noted that this fish consistently occupied spots of deep water, 5.1-8.6 feet, and low velocity, 0.2- 1.5 fps. This fish showed a familiarity with the underwater structure that enabled it to locate a deep underwater trough between sand ridges. 6.1.4.2 Movement In Response TO Ice Conditions . . 'IWo river ice conditions are identified as having different effect on the movement of the fish; (1) stable surface ice, and (2) unstable jam ice.' The stable surface ice was usually 1-2 feet thick, covered the entire river channel, and had a relatively smooth surface. The unstable jam ice often resulted from stacking of fractured ice blocks. This jam ice extended across the entire river channel or covered only a portion of it. It was constantly shifting and being moved downstream by the force of the current. Except during spring breakup, the unstable jam ice was observed only in the upper and middle regions of the study area. . Movement of the fish in response to ice conditions is also illustrated with sketches of selected river reaches in which one or more radiotagged fish were observed for varying periods of time. These sketches are presented in Figures 11-15, which represent the movement of radiotagged Colorado squawfish and razorback suckers under stable and unstable ice conditions. Each sketch is accompanied by a hydrogaph with the movements of the fish depicted in order to relate these to flow. . 6.1.4.2.1 Colorado Squawfish . Quantitative movement and habitat data presented elsewhere in this report show that the Colorado squawfish uses stable ice as a cover element. Local movement by squawfish under solid ice was no greater than movement in ice-free conditions, but the fish were often found in much shallower water underneath 31 .