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<br /> <br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />1 <br /> <br />Larvae and postlarvae: Factors potentially limiting the distribution and <br />abundance of young Colorado squawfish in the Yampa River include alteration of <br />natural flow and temperature regimens, and alteration of natural sediment and <br />nutrient loads. These in turn affect availability of nursery habitat in the <br />upper Green River basin. In addition, proliferation of non-native <br />competitors and predators in altered habitats is viewed as limiting. <br />Mortality of drifting larvae is directly related to flow, river <br />temperature, and backwater habitat availability. Young Colorado squawfish are <br />routinely collected in isolated pools in the Green River system (CDOW and FWS <br />data). These pools are formed when decreasing flows isolate bodies of water <br />from the main channel, Normal fluctuations in river level not only makes this <br />a gradual process but allows the trapped fish an escape route. However, <br />drastic fluctuations in river level, as characteristic of regulated systems, <br />could increase mortality of small fishes by cutting off escape routes and <br />thereby increasing potential for competitive interactions and exposure to <br />terrestrial predation. Herons, raccoons, garter snakes, and other animals <br />have been observed feeding on fishes trapped in isolated pools (Erman and <br />Leidy 1975, FWS unpublished data). <br />Impact of competition and predation by introduced fishes on growth and <br /> <br /> <br /> <br /> <br /> <br />survival of young Colorado squawfish has yet to be adequately assessed but <br />common use of backwater habitats by young Colorado squawfish and other small <br />fish species (FWS unpublished data, McAda and Tyus 1984) indicates the <br />potential for significant interspecific interaction. Dietary overlap between <br />young Colorado squawfish (TL<60mm) and other small fishes was noted by Jacobi <br />and Jacobi (1982). Karp et al. (1488) suggested that growth and survival of <br />young Colorado squawfish may be adversely affected by presence of similar- <br />34 <br /> <br />