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-25- Table 12. Average body condition coefficients (K) for brown, rainbow, and cutthroat trout in the Dolores River during 1991. 5/91 8/91 10/91 5/91 8/91 10/91 5/91 8/91 10/91 Species Metaska Campground Ferris Canyon Rock Stockpile (Mile 0.5) (Mile 6.0) (Mile 10.0) Brown 1.154 1. 317 1. 223 0.978 1.012 1.070 0.818 - - -- 1.008 Rainbow 1. 090 1. 235 1. 225 1. 016 1. 005 1. 049 0.911 - - -- 0.967 SRC 1.050 1.032 1. 314 0.990 - - - -- 1.084 0.895 - - -- 0.936 The data in Table 12 indicates body condition of the trout did increase in August and October compared to April 1991. This seems to indicate there was adequate food and habitat available for the trout density and biomass contained in the study areas. Again it must be emphasized density and biomass levels in the fall of 1991 were 50% to 80% lower than in October 1988. It should also be noted water temperatures did not approach near lethal levels in the summer of 1991, as was the case for prolonged periods in 1990. Body condition factor is also a function of energy (food) intake per unit time. Aquatic invertebrates (primarily insects and crustaceans) usually comprise the majority of a trout's food supply in streams. Riffles are the major aquatic invertebrate producing areas in streams. In the absence of adequate flushing flows, silt accumulates in the interstitial spaces of riffle areas and inhibits aquatic invertebrate production. Silt accumulation has been a major problem for the river in 1990 and 1991. There is.1itt1e doubt that the aquatic invertebrate fauna in the Dolores River below McPhee Dam has been adversely impacted by the lack of adequate flushing flows since 1988- 1989. Reduced body condition factors for the trout could be the end result of the silt accumulation problem as well. However, the cooperative agreement did not call for an evaluation of the silt accumulation problem or an assessment of the volume of water required to purge the river of accumulated silt. This problem would more appropriately be addressed by hydrologists and sediment transport specialists. . Technical expertise in this arena surely exists with the USBOR. In the final analysis, body condition is a function of density and biomass in relation to carrying capacity of the habitat rather than a true indication of habitat quality and/or quantity. An appropriate analogy would be to compare the body condition of beef cattle grazed on poor quality rangeland at a density of one cow per 500 acres. Under the low grazing density the herd body condition factor at the end of the summer might be quite good. Conversely, the herd body condition factor would be unacceptable for the herd grazed at a density of 100 cows/500 acres.