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<br />. <br /> <br />. <br /> <br />ATTACHMENT <br /> <br />STUDY METHODS/APPROACH <br /> <br />The Black Rocks population of humpback chub was discovered by G. Kidd in 1976 as <br />part of fisheries surveys by the COlorado Division of Wildlife (CDOW). Studies <br />by CDOW (Lytle et al. 1978, 1979, 1980, 1981; Haynes 1980, 1981; Wick 1980, 1981) <br />determined that the majority of the fish are restricted to a 1.6-km reach of the <br />Colorado River (RK 135.6-136.6) about 9 km upstream of the COlorado/Utah state <br />line. The distribution of the population was confirmed by Yaldez et a1. (1982), <br />and it was determined through radiotelemetry that the fish had a high fidelity <br />for very specific river reaches (Valdez and Nilson 1982, Ya1dez and Clemmer <br />1982). Kaeding et a1. (1985) classified 597 mature chubs from Black Rocks as 45' <br />Gila cvoha, 45' G. robusta, 10' G. sp., and <1' G. eleaans. Kaeding et al. <br />(1990) confirmed the fidelity of humpback chub to Black Rocks but considered it <br />one population with the Westwater Canyon population 20 Ian downstream. <br /> <br />Humpback chub were discovered in Westwater Canyon in 1979 by R. Valdez (Valdez <br />1980) during fisheries surveys by the U.S. Fish and Wildlife Service. Studies <br />from 1979 through 1981 (Yaldez et a1. 1982) determined that the population is <br />distributed for 13 km from Wild Horse Cabin (RK 124) downstream to Big Hole (RK <br />116). A monitoring program of adult humpback chub has been conducted by UDWR <br />since 1987 (MOretti et al. 1990). <br /> <br />Flow recorrunendations for the COlorado River have been made for Colorado squawfish <br />and razorback sucker, but may not be compatible with flow needs of humpback chub. <br />Since the humpback chub is a spring spawner, the magnitude, duration, and timing <br />of runoff flows may be critical to its reproduction and recruitment. <br /> <br />This study is designed to assess the effect of high spring flows on reproduction <br />and recruitment of humpback chub in Westwater Canyon and Black Rocks and the <br />impact of re-regulating the Aspinal Unit. Spawning and nursery requirements, <br />larval drift, recruitment, and reproductive isolating mechanisms of humpback chub <br />in Westwater Canyon and Black Rocks will be examined as they are affected by <br />flows and the operation of the Aspinal Unit. The study will employ <br />radiotelemetry as a means of identifying spawning sites. Drift net stations will <br />be established to assess the extent of larval drift, and low-velocity areas will <br />be seined to identify age-O nursery habitat. Spawning sites and nursery areas <br />will be mapped and described as these are affected by various flow levels. <br />successive year classes will be monitored to identify the river conditions that <br />maximize recruitment to the adult portion of the population. Also, the invasion <br />and proliferation of non-native species into Westwater Canyon and Black Rocks <br />will be assessed by analyzing catch-per-effort statistics of the ISMP Humpback <br />Chub Monitoring Program and past CRFP collections, and compare these with catch <br />rates of this study. The study will also examine the possibility of reproductive <br />overlap with roundtail chub invading the areas. <br /> <br />L/13 <br />