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<br />-20- <br /> <br />An in-depth discussion of the stages of a trout's life cycle (and the water <br />requirements necessary to sustain that life) is included here to illustrate <br />how and why the trout fishery has dramatically declined for the past 2 years. <br />A self-sustaining trout population must be able to complete all life stages. <br />This includes spawning, egg incubation, hatching, fry emergence, and <br />successful growth into and through the fingerling and juvenile life stages to <br />spawning adult. A suitable water supply (within the temperature range <br />necessary for survival) is indispensable for maintenance of a trout fishery. <br />The lack of water (in terms of volume, temperature, and duration of flow) <br />during 1990 has had serious consequences for the trout population in this <br />section of the river. <br /> <br />The phrase "reproductive successfl implies that spawning, egg incubation, <br />hatching, fry emergence, and recruitment have been completed, resulting in a <br />level of survival through the fry life stage adequate to establish a year <br />class of trout. This implies there are no habitat limitations impacting <br />subsequent life stages that would negate successful reproduction. <br /> <br />Monthly fry sampling efforts from June through August 1991 indicate brown <br />trout are the only salmonid species that demonstrated reproductive success in <br />1991. Evaluation of electrofishing data from previous years indicates brown <br />trout have been successfully spawning in this section of the Dolores River <br />since 1988, perhaps ,earlier (Table 10). No stocking of brown trout in this <br />section of the river has taken place since July 1988. In addition, the life <br />table information (Table 3A, in the Appendix) indicates brown'trout year class <br />strength has been increasing every year since 1988. The number of brown trout <br />in the 1990 year class (age 1+) was the most since 1988. Fry sampling in 1991 <br />(Table 10) indicates that the 1991 year class should be even larger! Age 1+ <br />cohort density at the FC and RSA sites in October 1991, is higher than the <br />1988 age 1+ cohort density at those two sites. <br /> <br />Numbers of young-of-the-year (YOY) brown trout taken during the October <br />electrofishing studies have steadily increased each year since 1988 as shown <br />in Table 10. The pattern of relative flow stability from October through <br />March each year since 1988 undoubtedly contributes to brown trout spawning <br />success. The detrimental effects of severe mid-winter flow fluctuations on <br />wild brown trout populations in Colorado has been documented on the Taylor <br />River below Taylor Park Dam (Nehring 1988) and on trout and salmon populations <br />elsewhere under varying flow conditions (Becker, et al. 1982, 1983; Reiser and <br />White 1981, 1983). <br /> <br />The winter flow volume in the Dolores River from October 1990 through March <br />1991 was over 50% lower than any previous year since the gates on McPhee Dam <br />closed in 1984 (see Table 1). Thus, based on increasing levels of YOY <br />fingerling brown trout in the river since October 1988 (Table 10), one can <br />conclude (from a brown trout reproduction standpoint ONLY) that flow quality, <br />quantity, and stability was adequate, even during the winter of 1990/1991. <br />