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l 1 j documented to migrate over 240 kilometers (150 mi) (Miller et al., 1983), moving to spawning sites in the summer, and then returning to other reaches for the remainder of the year. Even though feeding si tes are sometimes near spawning sites, it is possible that thes~ fish need to travel great distances in order to find sufficient food since they are large, and therefore require large and abundant food items (Stanford, 1994). Larval and young squawfish eat algae, plankton, invertebrates, and larval fish. When fish reach approximately 200 mm in length, they prey exclusively on other fishes (Muth and Snyder, 1995; Vanicek and Kramer, 1969) Colorado squawfish spawn when they are 6-7 years old (Behnke and Benson, 1983). They move to spawning sites on the receding limb of the hydrograph and spawn between late June and August, depending on the year. A typical spawning site has a gravel and cobble bar which is free of fine sediment, and a deep, low velocity staging area in close proximity (Tyus, 1990). A clean substrate is thought to be important since deep interstitial voids are needed for egg deposition, and Colorado squaw fish eggs are slightly adhesive (Tyus and Karp, 1989; Hamman, 1981). They spawn several times over a 2 day period, the eggs hatch after approximately 5 days at optimal temperatures of 20-22 degrees centigrade (Hamman, 1981; Marsh, 1985), and the larvae drift downstream. At this stage in their life cycle, backwaters appear to be essential to the growth of the fish since they provide a relatively warm and nutrient rich environment for growth, while minimizing energy expenditure for locomotion (Tyus and Karp, 1989; Osmundson et aL, 1995). Backwaters usually form at moderate and low flows when water no longer enters the upstream ends of side channels, and water ponds up into the side channel from downstream. They are warmer than the main channel because they I _c:J '.~.o.~.... oj I J J ) .J J I _I ~) j 3