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<br />suggest that they were cohorts from a spawning event. From these two individuals, a spawning date between <br />15-17 July was determined. <br /> <br />A single YOY Colorado pikeminnow was collected in 1996. That specimen was a 8.6 mm TL yolked- <br />mesolarvae taken on 2 August 1996 in a drift net at the Mixer sampling locality (RM 128,0). That individual <br />represents the only larval Colorado pikeminnow collected during drift net sampling at the Mixer. The 1996 <br />back-calculated spawning date for Colorado pikeminnow (18 July 1996) was similar to that predicted in 1995 <br />despite considerable difference in spring peak discharge (1995 - 12,100 cfs; 1996 - 3,450 cfs) and total annual <br />discharge. The 1997 drift netting samples did not yield any Colorado pikeminnow and the 1998 Mexican Hat <br />samples are still being processed (<200 bags of drift debris remain). <br /> <br />A comparison of 1995 and 1997 morning versus evening drift-net sampling indicated no significant differences <br />in catch rate or ichthyofaunal composition, However, the supplemental data produced by evening sampling <br />provided additional resolution to questions concerning drift patterns, In 1995, a drifting larval Colorado <br />pikeminnow was collected during the evening of2 August and an additional individual (larval) was collected <br />the following morning (3 August). Given the relative rarity of target species in the San Juan River and the <br />extremely limited number of larval Colorado pikeminnow and roundtail chub collected, we redesigned passive <br />drift-netting protocol so that sampling can be conducted during both morning and evening, In addition, we <br />instituted a sampling regime to be conducted during the last week of July or first week of August with nets to be <br />set every other hour when hydrologic and weather conditions allow. All drifting larval Colorado pikeminnow <br />were collected during this period. <br /> <br />Table 1. <br /> <br />Summary of larval and yay Colorado pikeminnow collected in the San Juan River <br />during larval drift-netting (1993-1998) and back-calculated dates of spawning. <br /> <br />Field <br />Number <br /> <br />MSB Number Total Date Date River Sample <br />Catalog specim. Length Collected Spawned Mile Method <br />Number <br />18098 1 9.2 26 Jul 93 08 Jul 93 53.0 drift netting <br />18099 I 9.2 27 Jul 93 09 Jul 93 53.0 drift netting <br />26187 1 9.2 02 Aug 95 15 Jul 95 53,0 drift netting <br />26191 1 9.0 03 Aug 95 17Ju195 53.0 drift netting <br />29717 8.6 02 Aug 96 18 Jul96 128,0 drift netting <br /> 5 <br /> <br />MH72693-2 <br />MH72793-2 <br /> <br />JPS95-205 <br />JPS95-207 <br /> <br />WHB96-037 <br /> <br />TOTAL <br /> <br />10 <br /> <br />! <br />) <br />I <br />\ <br />I <br />1 <br />i <br />( <br />E <br />