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<br />data, but unfortunately, low catch rates still result in non-normal data in some instances. It <br />was assumed that changes in CPE would reflect changes in the number of young Colorado <br />squawfish present each fall. <br />As the monitoring program progressed, concern arose about whether the mean CPE <br />value was giving a true index of the relative number of young-of-the-year Colorado <br />squawfish present in a given reach. It was possible that a high catch rate in an area with few <br />backwaters actually represented small numbers of squawfish concentrated in limited habitat. <br />An area with lots of backwaters and a low catch rate could contain more squawfish than an <br />area with higher CPE because the fish had more habitat to spread out in. ISMP participants <br />decided that the surface area of backwaters within each monitoring reach should be estimated <br />when sampling occurred. Knowing the amount of backwater habitat within the monitoring <br />reaches could produce a more accurate estimate of the number of post-larval Colorado <br />squawfish by multiplying mean CPE (fish/m2) by total area of backwaters (m2). However, <br />participants were reluctant to assume the added burden of measuring surface area of all <br />backwaters as they proceeded downstream so other possibilities were investigated. During <br />the same period, the Bureau was using remote sensing to quantify the effects of flow <br />fluctuations from Flaming Gorge Reservoir on habitat in the Green River (Pucherelli et al. <br />1988). They found that aerial video was a cost effective way of measuring the surface area <br />of backwaters and other habitats, so ISMP participants suggested incorporating video into the <br />monitoring program on a trial basis (Appendix B). This reports summarizes three years <br />(1989-1991) of post-larval Colorado squawfish monitoring data collected in conjunction with <br />aerial video. <br />METHODS <br />Aerial Video <br />Aerial video was acquired using a video camera attached to the front of a helicopter <br />flying at a consistent height above the river. Flights were timed to correspond as closely as <br />possible with collection of ISMP data. Bridges and other features were used to calibrate <br />scale and to adjust for the changing elevation of the rivers. The camera was connected to <br />monitors in the helicopter that could be viewed by the pilot and flight scientist during flight. <br />This allowed the helicopter pilot to keep the river channel in the center of the video image. <br />The flight scientist annotated the video tape with audio information about backwaters, side <br />channels, and general water conditions as they appeared from the air. These annotations <br />assisted the video interpreter in identifying features on the monitor in the laboratory. <br />4 <br />1 <br /> <br /> <br />1 <br /> <br /> <br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />