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Overall, the proposed action should beneficially affect both this species and the designated critical habitat; water quality changes associated with low flows may have adverse impacts under certain conditions when dilution flows are reduced. The proposed action also provides for adaptive management so that adjustments can be made to reflect new research and findings. Razorback sucker The razorback is endemic to the Colorado River Basin with a wide historical distribution. Historically the razorback occurred in the San Juan and Animas Rivers but little is known about population abundance (Holden, 1999). Throughout its range the species is now very rare with low to nonexistent recruitment. Small concentrations of razorback suckers have been reported in the inflow area in the San Juan arm of Lake Powell. Ryden (2000) reports that no wild razorback suckers have been collected in the San Juan River since 1988, when one individual was collected near Bluff (Holden, 1999). Overall this species is extremely rare or extinct in the San Juan River. The lower San Juan River is designated as critical habitat for the razorback as follows: New Mexico, San Juan County, and Utah, San Juan County. The San Juan River and its 100- year flood plain from the Hogback Diversion in T.29N.,R.16W., section 9 (New Mexico Meridian) to the full pool elevation at the mouth 9fNeskahai Canyon on the San Juan arm of Lake powell in T.41 S., R.ll E., section 26 (Salt Lake Meridian). Experimental stocking began in 1994 and these stocked fish have been observed in spawning condition. Larval fish were collected between Bluff and Montezuma Creek (Service, 2000a). The razorback's current distribution in the San Juan, counting introduced fish, is from Lake Powell to near the Hogback Diversion (RM 158). Razorbacks spawn on the ascending limb of the hydrograph, thus spawn earlier than the pikeminnow. Razorbacks use backwaters or flooded bottomlands prior to spawning; they generally spawn in runs over gravel or cobble. Backwaters and flooded bottomlands are important to complete the specie's life cycle; drifting larva enter backwaters where food sources can be abundant. \ The razorback decline has probably occurred for similar reasons as the pikeminnow's decline. Loss of backwaters and predation by nonnatives in remaining backwaters is a major problem as are nonnative fish and migration barriers. Overall, the proposed action should benefit this species and its critical habitat by improving riverine and backwater habitat conditions; and, as with the pikeminnow, periodic lower flows may adversely affect water quality in the razorback's habitat. Bonvtail and humpback chub These endangered fish do not occur in the San Juan River and would.not be affected by the operation 20 00629