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} ^~ Attachment 2 Reintroduction of Colorado squawfish into the upper mainstem Colorado River: Rationale and Justification A potential result of this study is the reintroduction of Colorado squawfish into historic, unoccupied habitat in the Colorado River above Palisade. From a preliminary habitat overview, this appears possible. The Colorado River between Glenwood Springs and the instream barriers above Palisade represents approximately 70-80 river miles, with about 50 miles occurring between Rifle and Palisade. For comparison, this reach contained approximately 1.5 to 2 times the mean annual flow of the Yampa River at Deerlodge from 1984-1989. Water temperatures at Cameo in Debeque Canyon annually exceeded 20 C during late June through August. Recent surveys on the Colorado River above Palisade suggest backwater habitat was relatively abundant, native suckers and roundtail chub were numerous and presence of non-native predaceous fish species in backwaters was relatively low. This upstream reach on the Colorado River was considered historic habitat, and appears to be suitable for reintroduction investigations. By comparison, existing occupied habitat for Colorado squawfish on the mainstem Colorado River consists of 55 river miles between Palisade and the State line, 15 miles of which is annually subjected to severe dewatering. If reintroduction were successful, occupied habitat in the Colorado River mainstem within Colorado for these two species would increase by 90-145, with concomitant increases in species' abundance. The current status of Colorado squawfish in the Colorado River within Colorado, as evidenced by lower capture rates, appears more precarious than elsewhere in the Upper Basin. USFWS biologists have reported this population to be relatively more rare in the upper mainstem Colorado River than in the other sub-basins. Results of standardized monitoring for adults in the upper mainstem Colorado River within Colorado indicate the catch rate indices generated are so Iow that further declines in abundance of Colorado squawfish within this reach would not be detectable. Spawning activity by squawfish in the occupied reach is known to occur, but spawning areas have not been clearly defined. Larval squawfish are present in the reach, but the magnitude of the number of larvae produced in the reach appears quite low and the effect of downstream transport of the larvae out of the reach via drift have not been studied. Two hypotheses may explain lack of recruitment to the adult population in the occupied reach. One is inadequate survival of young-of-the-year caused by temperature-induced slow growth. This would contribute to poor overwinter survival and extended vulnerability to predation. Another hypothesis is downstream transport of larvae via drift and displacement of early juveniles during high spring flows may cause the majority of potential recruits to the upper mainstem Colorado River population to be displaced into Lake Powell and lost due to intensive predation by non-native fish species. Reintroduction would serve to augment this diminished population and facilitate the understanding of recruitment problems as well as expand the species into historic habitat. The objective of reintroduction of Colorado squawfish in the