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<br />557 <br /> <br />activities, Ryden and Pfeifer (1996) suggested that the majority of the experimentally stocked San <br />Juan River razorback sucker reached sexual maturity in 1995-96 and that spawning of these <br />individuals might begin in the next two years. <br /> <br />At the November 1996 San Juan River Biology Committee integration meeting, it was suggested <br />that we expand a portion of our larval fish drift study to allow for documentation of razorback <br />sucker spawning. In other portions of the Colorado River basin this species reproduces at least <br />one month prior to Colorado squawfish. We know, from other Upper Colorado River basin <br />researchers, that one of the best means of collecting larval razorback sucker is through the use of <br />a passive collector that makes use of the fact that larval fish are attracted to light. The traps (light <br />traps) are set after dark and retrieved before dawn. The light is barely visible as it is only 2.25 <br />Volts and takes only two D-cell batteries to provide illumination. Once submerged, only the <br />styrofoam top of the trap remains visible. For these traps to operate efficiently, they need to be <br />set in very still waters (as opposed to drift nets which require flow). <br /> <br />If this additional collecting effort is approved, we plan to set light traps at every other night in <br />low-velocity habitats at or near both the Mixer and Mexican Hat sites. These traps would be set <br />after dusk and retrieved about four hours later. Fish taken under this portion of the study will be <br />preserved and identified at a later date. As spawning of razorback sucker begins in spring, <br />sampling for this species could not be done concurrent with Colorado squawfish sampling. <br /> <br />Sampling for razorback sucker will begin around April 1 and continue into May. We will our <br />sampling efforts with the Grand Junction office of U.S. Fish and Wildlife Service. Ryden and <br />Pfeifer will be tracking radio-tagged razorback sucker and be able to assess their reproductive <br />status. In addition, we will use information gained from spring razorback sucker tracking to <br />detennine the best site to establish light-trap stations. Light-traps will be set every other night and <br />the catch will be quantified based on catch per minute. We anticipate setting between 2-4 light <br />traps per site depending upon trap availability and physical characteristics of the study site. <br />Putative razorback sucker will be sent to Darrel E. Snyder, Colorado State University, for <br />verification. <br /> <br />Objectives: <br /> <br />1. Determine the temporal distribution of San Juan River ichthyoplankton in relation to the <br />hydrograph <br />2. Provide comparative analysis of the reproductive success of San Juan River fishes <br />3. Attempt to characterize downstream movement ofichthyoplankton <br />4. Attempt to validate presumed spawning period of Colorado River squawfish <br />5. Attempt to identify localities in the immediate proximity of the presumed Colorado squawfish <br />spawning bed for placement of drift nets in 1997. <br />6_ Collect light-trap samples oflarval fish at two sampling localities to determine if razorback <br />sucker reproduced in the San Juan River in 1997. <br /> <br />17 <br />