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<br />,'" {' ~ 11", / !It <br /> <br />. 0 ~ ! S 4A\tected Environment & Consequences <br /> <br />3-29 <br /> <br />Whirling disease has been linked to severe declines in the recruitment and survival of <br />young-of-the-year rainbow trout across 290 krn of four major trout streams in Colorado, <br />including the Gunnison River (Nehring, 1997), Drastic declines in rainbow trout <br />recruitment began in the upper Gunnison River in about 1990 or 1991, almost three years <br />before extensive testing of Myxobolus cerebralis, the parasite which causes whirling <br />disease, in wild trout began. In the lower Gunnison River in the Gunnison Gorge, <br />population level declines were detected at the age l+rainbow trout population in 1994, <br />the same years the presence of M,cerebralis was detected in wild trout. It is believed that <br />exposure of the lower Gunnison River to M.cerebralis probably occurred from the <br />passage of infected rainbow trout over the spillway of the Crystal Dam in 1993. <br />Significant and on-going declines in recruitment of age 1+ fish are dramatically altering <br />population density, structure, and biomass of wild rainbow trout in the Gunnison River <br />(Nehring, August 1997), <br /> <br />In addition to whirling disease, the presence or absence of suitable habitat for trout <br />reproduction and spawning, which is a function of flow and channel morphology, is <br />perhaps the most important factor influencing trout populations in the Gunnison River <br />because this river is managed as a wild trout fishery, Stable or increasing flows from <br />mid-October into spring seem best for natural reproduction and recruitment for brown <br />trout. Stable flows from April 1 to July 1 are also required to maximize spawning <br />success for rainbow trout. <br /> <br />In the FEIS, it was noted that studies based on the model Physical Habitat Simulation <br />Model (PHABSIM) conducted by the CDOW have shown that various flow-related <br />factors greatly influence the Gunnison River fishery: <br /> <br />. A flow of 200 cfs is an adequate minimum but substantial habitat gains occur between <br />200 and 300 ft3cfs. Available trout habitat drops dramatically below 200 cfs. <br /> <br />. Stable flows during the spawning and incubation period are needed to protect the <br />eggs. <br /> <br />. Medium-to-Iow stable flows provide the best survival conditions for trout swim-up <br />fry. The 45-day time period between June 1 and July 15 is probably the most critical <br />period in the Gunnison River for rainbow trout reproductive success. The April 15 <br />through June 15 period is critical for brown trout. If significant flow changes are <br />necessary, gradual incremental changes help prevent the total loss of an entire year <br />class of trout. <br /> <br />. Sudden inflows of sediment during flash floods cause fish kills until the sediment- <br />laden flows are diluted. <br /> <br />3.7.1.2 Uncompahgre River <br /> <br />Due to high turbidity, heavy siltation, poor substrate condition, poor water quality, bank <br />instability, high spring flows, and extremely variable summer flows, the Uncompahgre <br />River downstream from Montrose has had a poor sport fishery. With the development of <br /> <br />AS Lateral Hydropower Project <br /> <br />July 2000 <br /> <br />"; ~ <br /> <br />"'~' -' <br /> <br />-11 <br />i ,<f_' <br />J,; .'L,.;';';;"';,JJ;;" i~:~;:fui:;ji <br />