Laserfiche WebLink
<br />(':~I <br />Cl <br />I.... <br /> <br />Colonel John N Reese <br /> <br />DRAFT <br /> <br />11 <br /> <br />.~...1 <br /> <br />sucker (Bestgen 1990, Platania 1990, Platania et. al. 1991, Tyus 1987, <br />McCarthy and Minckley 1987, Osmundson and Kaeding 1989). <br /> <br />The existing scientific literature and historic accounts by local residents <br />strongly suggests that razorback suckers were once a viable, reproducing <br />member of the native fish community in the San Juan River drainage. <br />Currently, the razorback sucker is rare throughout its historic range and <br />extremely rare in the main stem San Juan River. <br /> <br />c., ., <br /> <br />Critical Habitat <br /> <br />Critical habitat has been designated within the 100-year floodplain of the <br />razorback sucker's historical range in the following section of the San Juan <br />River Basin (59 F.R. 13374). <br /> <br />New Mexico. San Juan Countv: and Utah. San Juan Countv. The San Juan <br />River from the Hogback Diversion in T. 29 N., R. 16 W., section 9 to the <br />full pool elevation at the mouth of Neskahai Canyon on the San Juan arm <br />of lake Powell in T. 41 S., R. 11 E., section 26. <br /> <br />BioloQV <br /> <br />Specific information on biological and physical habitat requirements of the <br />razorback sucker is very limited. localized extirpation of razorback suckers <br />from some localities, coupled with the species' continued decline in numbers <br />and distribution, has prompted some research; however, details of its life <br />history requirements, particularly in riverine environments, are still not <br />fully understood. <br /> <br />In general, a natural hydrograph with a large spring peak, a gradually <br />descending limb into early summer, and low stable flows through summer, fall, <br />and winter are thought to create the best habitat conditions for razorback <br />suckers. Prior to construction of large main stem dams and the suppression of <br />spring peak flows, low velocity, off-channel habitats (seasonally flooded <br />bottomlands and shorelines) were commonly available throughout the Upper Basin <br />(Tyus and Karp 1989; Osmundson and Kaeding 1991). The absence of these <br />seasonally flooded riverine habitats is believed to be a limiting factor in <br />the successful recruitment of razorback suckers in their native environment <br />(Tyus and Karp 1989; Osmundson and Kaeding 1991). Tyus (1987) and McAda and <br />Wydoski (1980) reported springtime aggregations of razorback suckers in <br />off-channel impoundments and tributaries; such aggregations are believed to be <br />associated with reproductive activities. Tyus and Karp (1990) and Osmundson <br />and Kaeding (1991) reported off-channel habitats to be much warmer than the <br />main stem river and that razorback suckers presumably moved to these areas for <br />feeding, resting, sexual maturation, spawning, and other activities assOciated <br />with their reproductive cycle. While razorback suckers have never been <br />directly observed spawning in turbid riverine environments within the Upper <br />Basin, captures of ripe specimens, both males and females, have been recorded <br />(Valdez et al. 1982; McAda and Wydoski 1980; Tyus 1987; Osmundson and Kaeding <br />1989; Tyus and Karp 1989; Tyus and Karp 1990; Platania 1990; Osmundson and <br />Kaeding 1991) in the Yampa, Green, Colorado, and San Juan Rivers. Sexually <br />mature razorback suckers are generally collected on the ascending limb of the <br />