Laserfiche WebLink
~ i G i C <br />-Five Miles----~ H ; D <br />Figure 2.-Schematic representing sampling protocol for the YOY Colorado squawfish portion of <br />the Interagency Standardized Monitoring Program (shaded areas represent seine hauls). <br />to the next backwater which was also sampled with two non-overlapping seine hauls. Colorado <br />squawfish were measured, counted, and released alive. No other fish from the second backwater <br />were preserved or counted for ISMP. However, a second study evaluating the abundance of <br />introduced species in conjunction with ISMP counts or preserves all specimens collected from all <br />backwaters in the Colorado River. These data will be reported elsewhere. <br />After sampling the second backwater, investigators proceeded downstream to the top of the next <br />5-mile reach before sampling again. Samples were not taken within a 5-mile subreach if no <br />backwaters meeting ISMP's criteria were found. The first backwater sampled in each 5-mile subreach <br />was considered a primary backwater, and the second backwater sampled was considered a secondazy <br />backwater. Although there were some differences in how nonendangered fish were handled in <br />primary and secondary backwaters, there was no difference in sampling technique. Therefore, catch <br />rates for YOY Colorado squawfish were calculated using combined data from both primary and <br />secondary backwaters. <br />Physical pazameters were also measured at each sample site: water temperature in the backwater <br />and in the main channel was recorded (± 1°C); length and width of each seine haul, and total length <br />and average width of each backwater was measured (± 1 m); maximum depth of the backwater, and <br />maximum and average depth of each seine haul was measured (± 0.1 ft, converted to cm); and <br />average substrate size was estimated for each seine haul and for the backwater as a whole. <br />Data Analysis <br />The relative density, or catch per effort (CPE), of YOY Colorado squawfish was determined by <br />the number collected per area of backwater swept with the seine. CPE for each reach was calculated <br />as the mean of all seine hauls taken within the reach. Because of the relatively low number of <br />Colorado squawfish collected every year, data aze not normally distributed-an assumption required <br />by many data-analysis techniques. McAda (1989a) investigated several methods of data analysis for <br />the monitoring program and suggested using geometric-mean CPE rather than the more standard <br />calculation of arithmetic mean. The geometric mean is calculated by using a log transformation <br />(loge(CPE + 1)) on individual seine hauls before calculating the mean. The mean of the log values is <br />then transformed back to a standard value. A log transformation improves the normality of CPE <br />data, but unfortunately, low catch rates still result in non-normal data in some instances. Change in <br />5 <br />' ~ ~ ~ ~ <br />j j ~ I}oumstream ~ F E I ~ <br />