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<br />availability at recommended releases from the Aspinall unit on the Colorado River to <br />habitat utilized by young Colorado squawfish and the number of young squawfish <br />present during the autumn nursery period; and 3) the effect of flow manipulation and <br />habitat availability on growing season and size of Colorado squawfish young-of-the- <br />year as it relates to potential overwinter survival, <br /> <br />Recommendations: None. <br /> <br />B: (Colorado) The primary emphasis of this work is to understand how modified river <br />flows have affected endangered fish habitat in the upper Colorado River. Work began <br />in FY -93 in the 15- and l8-mile reaches and expanded in FY -94 to H011!ethief and <br />Ruby canyons. These two canyon reaches occur between the 18-mile reach and the <br />Utah border. Initial work involved obtaining aerial photographs to document physical <br />changes that have occurred in the river over time. Photographs from 1937, 1954, <br />1968, and 1986 were obtained and important features on these photographs were <br />digitized into a GIS system. Important changes in the river channel were then <br />summarized. In addition to the GIS work, transects were set up at important habitat <br />sites to monitor change in the channel over time. Work tl1rough 1994 was summarized <br />by Van Steeter et al. (1995). <br /> <br />Recommendations: Continue project as currently proposed. <br /> <br />45 ASP-C: FLOW EFFECTS ON YOY SQUA WFISH <br /> <br />This study began in 1990, was incorporated into the Aspinall Studies when they began <br />in 1992, and continues through 1996. The study is testing hypotheses developed based <br />on analysis of data collected from 1982-1985 and by the Interagency Standardized <br />Monitoring Program (ISMP). The hypotheses are: I) relative abundance of age-O <br />Colorado squawfish in the Colorado River is greatest during years with a natural <br />hydrograph and maximum-annual discharges 000,000-40,000 cfs and relative <br />abundance is reduced in years with higher or lower maximum-annual discharges; <br />2) length of growing season affects over-winter survival of yay Coloradg squawfish; <br />and 3) high spring flows and a natural hydrograph reduce non-native fish populations. <br />The study has three main parts: I) rivef-wide larval sampling using the same basic <br />sampling design used in 1982-1985; 2) fall ISMP sampling with all species collected <br />from all seine hauls identified and counted to determine relative abundance of the <br />introduced species coexisting with Colorado squawfish; and 3) spring sampling in the <br />lower Colorado River (RM 0-110) using the same sampling design as ISMP to assess <br />, numbers of Colorado squawfish and sympatric fishes after their first winter. <br /> <br />Recommendations: Larval dip-net sampling was not done in FY 95 and will not be <br />done in FY 96. Spring and fall seining should continue through 1996. <br /> <br />A-Ii <br />