Final Programmatic Biological Opinion for Bureau of Reclamation's

27During 1986-1988, 17 adult Colorado pikeminnow were captured in the 15-Mile Reach duringApril-June and radio-tagged. The fish exhibited a diversity of localized movements throughoutthe Grand Valley but spent a major part of their time in the 15-Mile Reach. Two remained in thereach throughout the estimated spawning period (Osmundson and Kaeding 1989).In a study by McAda and Kaeding (1991), a suspected prespawning aggregation of adultColorado pikeminnow was observed in mid-July of 1982 at river mile 178.3 in the 15-Mile Reach.In the first observation, three radio-tagged fish were tracked to one riverine pool area, and nineadults at or near spawning condition were then captured there after limited net sampling efforts.The aggregation occurred a few days after mean daily water temperature had reached 20 o C andduring a time when runoff flows were dropping off sharply. A second aggregation was noted atriver mile 175.3, 12 days after the initial observation. Drifting trammel nets through an areaoccupied by two fish equipped with transmitters yielded an additional male Colorado pikeminnowin spawning condition. During this same time period, an adult female was captured near river mile175 that weighed nearly 1 pound more than when previously captured a month earlier, suggestingthe development of spawning (gravid) condition. Two Colorado pikeminnow larvae weresubsequently collected within the 15-Mile Reach.During 4 years (1982-1985) of larval sampling throughout the Grand Valley, 100 larvalpikeminnow were collected with fine-mesh hand nets from the two Colorado River reachesimmediately upstream and downstream of its confluence with the Gunnison River (McAda andKaeding 1991). Although the sampling effort was similar in the two river reaches, 98 percent ofthe larval captures occurred downstream of the Gunnison River confluence. Only two (2 percent)of the larvae were collected from the upstream reach. These observations may indicate that mostfish were spawned in the downstream reach or that the larvae were deposited in the upstreamreach and drifted downstream to the area where most of the captures were recorded. In 1995,drift nets set in the lower portion of the 15-Mile Reach captured 3 Colorado pikeminnow larvae(Anderson 1998).No postlarval young-of-year Colorado pikeminnow greater than 25 mm total length werecollected from above the Gunnison River confluence in fall collections from 1986-1994; however,one yearling-sized individual was captured there in 1986 (Osmundson and Burnham 1998). Atotal of 122 Colorado pikeminnow were collected in the 31-Mile Reach downstream of theconfluence of the Gunnison River during 1982-1996 (McAda and Ryel 1999). The 1982-1984catch rate of young-of-year Colorado pikeminnow in the 10-Mile Reach immediately downstreamof the confluence of the Gunnison River (river miles 160-170) warranted classification of thisreach as a "Young-of-Year Nursery Area" by the Basin Biology Subcommittee (USFWS 1984).Catch rates of adult (> 500 mm long) Colorado pikeminnow in the 15- and 18-Mile Reaches ofthe Grand Valley are significantly higher than in any other portion of the Colorado River(Figure 1). In the 15-Mile Reach, adults are most abundant during spring in a 1.3-mile segmentbetween river miles 174.4 and 175.7, particularly in two gravel-pit ponds that were accessible