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I I I I I I I I I I I I I I I I I I I sand shiners (2.37), and fathead minnows (2.33) in backwaters are greater than the catch rate for Colorado squawfish (1.73). Young-of-the-year channel catfish (7.75) dominated the catch rate of fishes in shorelines, where there was generally low velocity, shallow water, and the substrate primarily sand. The relatively high catch rate of this species in most habitats sampled indicates that the 1987 year class was strong. As in 1986, the relatively high catch rate of Colorado squawfish in isolated pools in 1987 (3.79) is a disturbing statistic. Seemingly, all fish in this habitat are stranded and doomed to death by desiccation, high temperature, oxygen depletion, or predation. This may be true in some cases, but, it has been observed in late summer that previously isolated pools were inundated by rising flows from increased rainfall. Many of the fish in these pools may be able to survive a month or so of isolation and return to the river. Use of these secluded habitats may be a coincidental survival strategy, since the warm isolated pools harbour an abundance of food for young fishes; the YOY squawfish trapped in isolated pools appear healthy and larger than their counterparts in the main river. The presence of predators, such as largemouth bass, green sunfish or black bullheads, can doom many of the small trapped fishes. But, juvenile squawfish in isolated pools may have the advantage over other species since they could be the principal predators (see photos 9-12 in Appendix D). Isolated pools were dominated by the non-native red shiner (13.79/ square meter); and fathead minnows (3.91), speckled dace (2.32), black bullheads (1.99), channel catfish (1.40), and sand shiners (0.99) were also numerous. Drift Nets Although a total of 116 sets were made with larval drift nets, only 74 fish were captured with this gear type (Table 18). This compares to a total catch of 75 fish .for 136 sets in 1986. The predominant species in drift nets in 1986 and in 1987 was the channel catfish (0.89 fish/1000 cubic feet of water in 1987). Roundtail chub (0.80) and red shiner (0.57) were found in low numbers in the drift, and only one Colorado squawfish was captured in drift samples in 1987. In 1986, three squawfish were captured in drift nets. The catch of larval fishes with drift nets in the Cataract Canyon Region is considered low because of any or all of the following possibilities: 1. Sampling in July and August could be too late to capture emerging and drifting fishes which probably hatch in the region primarily in June. 2. According to Valdez et ale (1985), the majority of drift in the upper Colorado River is composed of native species that could be emerging in June, while non-native species emerging in July and August are not likely to be captured in drift nets, since they do not appear to be as abundant in the drift (Robert T. Muth, personal comrrnmication, Grand Junction, Colorado, February 24, 1987). 3. Reproduction by native fishes in the Cataract Canyon Region could be low, and the majority of native species (especially Colorado squawfish) are being transported from spawning areas further upstream. 16