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II ..., IJ.)"t In a 1988 sutewide nonpoint water quality assessment cepo" the Colorado Water Quality Control Division identified a slight suspended sediment problem between Indian Creek: and Navajo Reservoir attributable mainly to the geology of that area. No chemical water quality problems or concerns were identified. On the mainstem of the Piedra River adequate streamrlow is the most imponant factor in maintaining cool temperatuces in the summer and in limiting the extent of ice formation in the winter. Streamside vegetation can moderate temperatures on the tribuuries where the stream channel is not as wide. Larger fish will "stack up. in deep pools to conserve energy. Fish will also use cover to avoid or limit exposure to temperature extremes. In the wimer, smaller fish will wedge themselves into cobble substrates to minimize energy expenditure. Brown trout are known to use tlat surfaces of rocks to lie against. thus conserving energy. While spawning requirements differ among the species found in the Piedra River, they all require a clean. gravel substrate with little to no embedded fine sediments. Trout and suckers deposit their eggs in redds fanned in gravels. Sculpin and dace deposit their eggs in the spaces betWeen cobbles and the eggs adhere to the rocks. All of the above species are spring/summer spawners with the exception of brook and brown trout. which spawn in the fall. See Figures F and G. Speckled dace often spawn twice a year, once in the early summer. and then in conjunction with the late summer and fall peaks. Their life span is relatively short, thus egg and juvenile development is rapid. The tributaries of the Piedra play an important role in spawning; young fish and spawning adults were found in the First Fork and its tributaries and in Sand and Weminuche Creeks during the 1991 population surveys. The perennial tributaries also have resident trout populations. Many young trout were found in smaller tributaries such as Sheep, Indian, and O'Neal Creeks during 1991 surveys. These smaller tributaries are important for spawning and rearing. Brown trout egg incubation occurs when streamtlows are the lowest (November through ~arch or April). To limit desiccation of eggs, flows should nO[ be artificially decreased below those which occur at the time of egg deposition. Rainbow trout fry emerge during the high flows associated with snowmelt and their survival is largely dictated by the availability of complex arrangements of branches. root wads. logs. vegetation. and large substrate. These fonns of cover. especially along the stream edges, provide shelter from velocity and predators. No abrupt changes in flow should occur during or shorny after fry emergence which might strand the fry in isolated pockets of water along the stream banks or which might tlush them out of rearing areas. Successful rearing of juvenile tish is dependeD[ upon adequate cover for prmection from predators. including larger tish. and on the availability of areas with relativelv low velocities . .' such as areas of shallow water along the edges of the channel. As the fish grow and can swim in higher velocities they will move into stronger currents where feeding is better. At this stage, the habitat available to juvenile fish depends on the amount and type of cover combined with the ability [0 escape predation (Meehan. 1991). Because fish are competitive. more tish can occupy a given area and a variety of age classes can coexist if they cannot see each other. Vegetation. woody debris. boulders, and turbulent water provide this t}'Pe of cover by limiting sight distance. Page 11