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weakly positive. Thus there was no evidence of increasing numbers of one of these three species depressing numbers of Colorado squawfish within backwaters as would be expected if competition or predation were occurring. The correlations probably reflect similar habitat use rather than lack of competition or predation. Haines and Tyus (1990) also found no evidence that abundance of one species in a backwater was associated with reduced numbers of another. Recent laboratory studies have addressed the issues of competition and predation. Karp and Tyus (1990a) found that red shiner and fathead minnow were more aggressive than small Colorado squawfish in laboratory studies and postulated these species could adversely affect growth or survival of YOY Colorado squawfish. Beyers et al. (in review) documented competition between Colorado squawfish and fathead minnow in aquazia when limited food resources were present. Predation was also demonstrated in the laboratory with controlled studies (Muth and Beyers in review). Rupert et al. (1993) collected adult red shiners from the lower Yampa River that contained fish larvae in their stomachs. Although they did not identify larval Colorado squawfish in the samples, the high abundance of red shiner in the basin, sympatry with YOY Colorado squawfish, and their consumption of fish larvae is cause for concern. Although negative effects aze not easily documented with ISMP or similar field data, these laboratory studies suggest that introduced fishes are increasing mortality of YOY Colorado squawfish. Potential Modifications to ISMP In 1989, investigators became concerned that mean CPE ,alone was not providing an accurate index of relative abundance of YOY Colorado squawfish every fall. They felt estimates of relative abundance could be improved by measuring the number and surface azea of backwaters in every reach. Therefore aerial video was incorporated into ISMP on a trial basis to examine its potential for measuring number and surface area of backwaters and improving the annual estimate of relative abundance. Participants felt that a gross estimate of YOY Colorado squawfish numbers could be obtained by multiplying mean CPE by total azea of backwaters. McAda (1993) evaluated 3 yeazs of ISMP data collected in conjunction with aerial video enumeration of backwater number and azea. He concluded that aerial video did not significantly improve the annual estimate of relative abundance and did not justify the additional cost. He recommended that collection of aerial video as part of YOY Colorado squawfish monitoring be discontinued; therefore the video data aze not presented again. However, McAda (1993) also suggested aerial video of short river reaches in conjunction with intensive ground truthing may still be appropriate for specific studies-such as the nursery habitat investigation being conducted by UDWR. However, there may be other ways that ISMP could be improved. ISMP data are highly vaziable, which makes detecting important differences among yeazs and reaches difficult (McAda 1989a). Unfortunately, increasing sample effort does relatively little to improve statistical reliability of data analyses. McAda (1989a) concluded that the extra cost of collecting additional samples was not justified by the small increase in the power of any statistical analyses that might be done. ISMP already samples two backwaters per 5-mile subreach which is often the maximum number located in many subreaches every yeaz and increasing the number of sampling sites might not be feasible anyway. However, some backwaters aze quite lazge and deep. It might be appropriate to increase the number of seine hauls taken in the lazge backwaters to increase the certainty of getting a reliable sample. ISMP guidelines originally suggested that investigators sample at least 25% of the surface area of all backwaters sampled. However, that requirement was dropped when participants felt it difficult to accomplish (McAda 1989c). 23