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Table 5.-Correlation (Pearson Correlation Coefficient), by sampling reach, of mean total length of YOY Colorado squawfish during fall ISMP sampling with seasonal flow events at the nearest USGS gaging station, 1986-1992. Mean of 30 Highest Days Around Mean -Monthly S treamflow (CFS) Mean-Daily Highest Daily Reach Flow Flow A r P Ma Y Jun Jul Y Au g Se P 1 -.45 -.54 -.36 -.47 -.52 -.64 -.54 -.57 2 -.46 -.37 -.20 -.30 -.36 -.36 -.14 -.36 3 -.83° -.88° -.87° -.9(1° -.85° -.87° -.86° -.81° 4 -.84° -.92° -.86° -.89° -.93° -.9ti -.79° -.66 °Significant at P<.OS Habitat Use As observed earlier, previous researchers (e.g. Tyus and Haines 1991) determined that YOY Colorado squawfish primarily use backwaters, which were the only habitats sampled during ISMP. In addition, restrictions on size and depth of backwaters sampled, and the sampling design of ISMP further limit our ability to address habitat selection with these data. However, comparisons were made among the major habitat characteristics measured (backwater size, depth, and water temperature) during ISMP. YOY Colorado squawfish occupied backwaters with a wide variety of physical- features. In years of high abundance, most backwaters sampled contained YOY Colorado squawfish (Table 6). More than 70% of all backwaters sampled in the lower Green River (Reach 3) over the 7-year study contained Colorado squawfish. In 1988 and 1989, years of very high CPE, almost all backwaters sampled in Reach 3 contained at least 1 Colorado squawfish (and usually quite a few more). Reaches (or years) with lower mean catch rates typically had a lower percentage of backwaters that contained YOY Colorado squawfish (Table 6). Surface area of backwaters was estimated by multiplying backwater length by average width. Backwaters of a wide range of sizes were sampled but 50% of all backwaters sampled over the 7-year study were less than 650 m2 in surface area. Seventy-five percent were less than 1,300 m2 and 909 were less than 2,400 mZ. However, backwaters as large as 5,200 m2 were sampled over the course of the study. For ANOVA, backwaters were grouped into four size categories: < 350 m2, 350 to 649 mZ, 650 to 1,349 mZ, and > 1,349 mz. For descriptive histograms, backwaters were grouped into 19 size categories based on 200 m2 increments, the last category included all backwaters z 3,800 m2. Independent t-tests compared surface area of backwaters that contained at least one Colorado squawfish with surface area of backwaters that contained none.2 ZDescriptive histograms and tables summarizing ANOVA and t-tests of habitat variables are available from the senior author. 14