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<br />~" " <br /> <br />"001'615 <br /> <br />Juveniles <br />Collection of2- 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 <br />ability make them difficult to catch using electro fishing or seines; hence they are not commonly <br />caught. As stocked YOY grew in the San Juan River, they were captured in relatively large <br />numbers through seining and electrofishing, especially above Mexican Hat, Utah. In 1997,38 <br />yearlings (stocked in 1996) were caught during main channel electrofishing (Ryden 2000a). They <br />ranged in size from 124 to 235 mm TL and were primarily captured in shallow shoreline habitats. <br />Most were found between the Hogback Diversion and Mexican Hat, Utah, and three were collected <br />in RM 18 near the Lake Powell interface. The 1- and 2-year-old fish were collected in 1998 and <br />1999, and growth ofthese fish was comparable with, or greater than, growth seen in other Upper <br />Basin rivers (Trammell and Archer 2000). This indicated that young Colorado pikeminnow found <br />quality habitat in the San Juan River. This size-class appeared to use the greatest variety of <br />habitats and was likely the least selective. Therefore, no specific key habitats were identified for <br />juveniles and, based on the San Juan River collections, suitable habitat for this age class is found <br />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 <br />were not as well understood as those of Colorado pikeminnow. Adult and larvae razorback sucker <br />were found in both riverine and reservoir habitats in the Colorado River Basin, but very few YOY <br />had been collected in recent times. Tyus and Karp (1989) identified razorback sucker spawning <br />sites in the Green River and collected larvae, but it was not until 1994 that YOY razorback sucker <br />were found in flooded bottomland habitat of the Green River (Modde 1996) and a more-complete <br />picture of their habitat use emerged. These studies indicated that this species spawns on maiJi <br />channel gravel bars near the hl<ight of peak spring flow and that they show fidelity to certain bars <br />(Modde and Irving 1998). The young hatch in a few days, drift downstream, and enter flooded <br />bottomlands that are connected to the main channel during high flow. Backwaters and other low- <br />velocity habitats are also used by larvae, but flooded bottomJands are thonght to hp a key habitat <br />for survival of larvae It is not known when young razorback sucker return to the main river. <br />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 <br />of main channel- and backwater-type habitats, the latter are used especially prior to and during the <br />spawning period as apparent resting areas between spawning events on main channel cobble bars <br />(Bestgen 1990, Minckley et al. 1991). <br /> <br />September 2000 <br /> <br />3-9 <br /> <br />Program Evaluation Report <br />