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<br />C) <br />C-) <br />.... <br />co <br />00 <br />i'=' <br /> <br />Juveniles <br />Collection of 2- to 4-year-old wild Colorado pikeminnow (100 to 300 mm TL) is infrequent in the <br />Colorado River system. This age class appears to use a variety of habitats, including main channel <br />habitats that are swift and, therefore, difficult to seine. Their relatively small size and swimming ability make <br />them difficult to catch using electrofishing or seines; hence they are not commonly caught. As stocked <br />YO Y grew in the San Juan River, they were captured in relatively large numbers through seining and <br />electrofishing, especially above Mexican Hat, Utah. In 1997, 38 yearlings (stocked in 1996) were caught <br />during main channel electrofishing (Ryden 2000a). They ranged in size from 124 to 235 mm TL and were <br />primarily captured in shallow shoreline habitats. Most were found between the Hogback Diversion and <br />Mexican Hat, Utah, and three were collected in RM 18 near the Lake Powell interface. The 1- and 2- <br />year-old fish were collected in 1998 and 1999, and growth of these fish was comparable with, or greater <br />than, growth seen in other Upper Basin rivers (Trammell and Archer 2000). This indicated that young <br />Colorado pikeminnow found quality habitat in the San Juan River. This size-class appeared to use the <br />greatest variety of habitats and was likely the least selective. Therefore, no specific key habitats were <br />identified for juveniles and, based on the San Juan River collections, suitable habitat for this age class is <br />found throughout the river between Hogback Diversion and Mexican Hat, Utah, and in the lower 20 miles <br />of the river. <br /> <br />Razorback Sucker <br />When the SJRIP was initiated in 1991, the life history and habitat requirements of razorback sucker were <br />not as well understood as those of Colorado pikeminnow. Adult and larvae razorback sucker were found <br />in both riverine and reservoir habitats in the Colorado River Basin, but very few YOY had been collected <br />in recent times. Tyus and Karp (1989) identified razorback sucker spawning sites in the Green River and <br />collected larvae, but it was not until 1994 that YOY razorback sucker were found in flooded bottomland <br />habitat of the Green River (Modde 1996) and a more-complete picture of their habitat use emerged. These <br />studies indicated that this species spawns on main channel gravel bars near the height of peak spring flow <br />and that they show fidelity to certain bars (Modde and Irving 1998). The young hatch in a few days, drift <br />downstream, and enter flooded bottomlands that are connected to the main channel during high flow. <br />Backwaters and other low- velocity habitats are also used by larvae, but flooded bottomlands are thought <br />to be a key habitat for survival oflarvae. It is not known when young razorback sucker retwn to the main <br />river. Recent studies using stocked fish (T. Modde, USFWS, Personal Communication) suggested that <br />they may be able to spend an entire year in some off-channel bottomlands. Adults used a variety of main <br />channel- and backwater-type habitats, the latter are used especially prior to and during the spawning period <br />as apparent resting areas between spawning events on main channel cobble bars (Bestgen 1990, Minckiey <br />et al. 1991). <br /> <br />September 2000 <br /> <br />3-9 <br /> <br />Program Evaluation Report <br />