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<br />1321 <br /> <br />Since the initiation of this research program, five larval Colorado pikeminnow have been <br />collected. The two YOY Colorado pikeminnow collected in 1993 (at Mexican Hat) were the <br />same length (9.2 mm TL; MSB 18098, 18099) and were taken on consecutive days in late July <br />(26-27). From these two individuals, we determined the date of spawning to be about 8-9 July <br />1995. <br /> <br />Two larval Colorado pikeminnow were taken at Mexican Hat during the 1995 larval fish passive <br />drift-netting study. The first specimen, 9.5 mm TL mesolarvae (MSB 26187) was taken between <br />2114-2310 hours on 2 August 1995. The next morning (3 August 1995) between 0531-0800 <br />hours, a second Colorado pikeminnow, 9.0 mm TL mesolarvae (MSB 26191) was collected. <br />The similar size and developmental stage of these two individuals, in combination with the fact <br />that the two fish were collected within 12 hours of each other, strongly suggest that they were <br />cohorts from a spawning event. From these two individuals, a spawning date between 15-17 <br />July was determined. <br /> <br />A single YOY Colorado pikeminnow was collected in 1996. That specimen was a 8.6 mm TL <br />yolked-mesolarvae taken on 2 August 1996 in a drift net at the Mixer sampling locality (RM <br />128.0). That individual represents the only larval Colorado pikeminnow collected during drift <br />net sampling at the Mixer. The 1996 back-calculated spawning date for Colorado pikeminnow <br />(18 July 1996) was similar to that predicted in 1995 despite considerable difference in spring <br />peak discharge (1995 - 12,100 cfs; 1996 - 3,450 cfs) and total annual discharge. The 1997 drift <br />netting samples did not yield any Colorado pikeminnow and the 1998 samples are still being <br />processed (>500 bags of drift debris). <br /> <br />A comparison of 1995 and 1997 morning versus evening drift-net sampling indicated no <br />significant differences in catch rate or ichthyofaunal composition. However, the supplemental <br />data produced by evening sampling provided additional resolution to questions concerning drift <br />patterns. Given the relative rarity of target species in the San Juan River and the extremely <br />limited number of larval Colorado pikeminnow and roundtail chub collected, we redesigned <br />passive drift-netting protocol so that sampling can be conducted during both morning and <br />evening. In addition, we instituted a sampling regime to be conducted during the first week of <br />August that called for nets to be set every other hour when hydrologic and weather conditions <br />allow. <br /> <br />,."<. <br /> <br />The lack of adult Colorado pikeminnow with functioning radio tags had, until 1998, precluded <br />our attempts to sample the drift below the putative spawning bar during the presumed period of <br />spawning by this species. During August 1998, we conducted an intensive six day sampling <br />effort (ca. 14 hours/day) employing drift-nets and the Moore Egg Collector (MEC) in an area <br />immediately downstream of a putative Colorado pikeminnow spawning bar. Researchers from <br />Miller Ecological Associates had been tracking radio-tagged adult Colorado pikeminnow in that <br />area for at least a week and, given the behavior of the fish, believed that spawning had occurred. <br />Our sampling effort (conducted several days after the hypothesized initiation of spawning) <br />yielded 152 collections and as many sample bags of debris (n=238) as was collected at either <br /> <br />Work Plan FY99.wpd <br /> <br />6 <br /> <br />Budget and Work Plan FY99 <br />