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<br />556 <br /> <br />SAN JUAN RIVER LARVAL FISH PASSIVE DRIFT -NETTING <br />& LIGHT-TRAPPING STUDY <br />1997 WORK PLAN <br />Division of Fishes <br />Museum of Southwestern Biology <br />Department of Biology <br />University of New Mexico <br /> <br />Background: <br /> <br />Beginning in spring 1995, personneLfrom the Division of Fishes, Museum of Southwestern <br />Biology (MSB), at the University of New Mexico assumed responsibility for the San Juan River <br />larval fish passive drift-netting study. This project, formerly conducted by the Utah Division of <br />Wildlife Resources, continued with only minor changes in sampling protocol. Data coUected from <br />this research activity provided several discrete types of information on the fishes of the San Juan <br />River. Data that can be obtained on the endangered fishes of the river include determining <br />approximate spawning period, identifYing approximate location of spawning sites, and assessing <br />affects of annual hydrology (and temperature) on their reproductive activities. Similar data are <br />also obtained for other members of the ichthyofaunal community and contrasted with previously <br />drift-net sampling to assess the affects of that year's flow regime on fish reproduction. Samples <br />coUected during this research program were and wiU continue to be processed and curated by Fish <br />Division personnel at the University of New Mexico. <br /> <br />Since assuming responsibility for this phase of the research program, we have collected three <br />larval Colorado squawfish. Two larval Colorado squawfishwere taken at Mexican Hat during the <br />1995 larval fish passive drift-netting study. The first specimen, 9.5 mm TL mesolarvae (MSB <br />26187) was taken between 2114-2310 hours on 2 August 1995. The next morning (3 August <br />1995) between 0531-0800 hours, a second Colorado squawfish, 9.0 mm TL mesolarvae (MSB <br />26191) was coUected. The first larval Colorado squawfish from the Mixer site was coUected on 2 <br />August 1996 (MSB 29717). These specimens were coUected during years with extremely <br />different flow regimes. <br /> <br />A comparison of 1995 morning versus evening drift-net sampling indicated no significant <br />differences. However, the supplemental data produced by evening sampling provided additional <br />resolution to questions concerning drift patterns. Given the relative rarity of target species in the <br />San Juan River and the extremely limited number of larval Colorado squawfish and roundtail chub <br />coUected, we will propose to redesign passive drift-netting protocol for 1997 so that sampling can <br />be conducted during both morning and evening. <br /> <br />In 1994, a total of 672 razorback sucker were stocked in the San Juan River between Bluff, Utah <br />and the Hogback, New Mexico. Mean length and mass of those individuals, at the time of <br />stocking, was about 400 mm TL and 710 g, respectively. In 1995, 13 of the recaptured razorback <br />sucker were tuberculate males and six of those individuals were ripe. In their 1995 report of <br /> <br />16 <br />