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13:.10 reach of the river. We conducted sampling forays (n=6) at approximately bi-weekly intervals from 17 April (first trip - no larval suckers) to 6 June 1998 between the Four Corners drift-net station (RM 128) and Bluff (RM 80) and used both active and passive sampling techniques to collect larval fish. The primary sampling method was a fine mesh larval seine (in 1998, we collected more larval sucker in a single seine sample than in all of the 1997 light trap samples). Passive sampling techniques were both drift-netting and the use of light-traps. Drift-nets were set periodically to determine if larval sucker comprised a significant portion of the drift community while light-traps were set adjacent to campsites if appropriate aquatic mesohabitats could be located. An inflatable raft was used to traverse this river reach and allow investigators the opportunity to sample habitats that were either not formerly accessible or observable under the constraints of the previous sampling protocol. The 1998 sampling protocol resulted in the collection of over 13,000 specimens, the majority of which were larval catostomids. This 43-fold increase in number of specimens, as compared with 1997, provided substantially better resolution of spawning periodicity of the sucker community. In addition, the 1998 samples produced enough individuals for investigators to determine, with a high degree of confidence, if razorback sucker reproduction occurred in the San Juan River during that period. None of the aforementioned information was obtainable from 1997 light-trap samples. Until larval razorback sucker have been collected, we recommend that the protocol currently being used (utilizing as many sampling methods as possible to collect as many larval sucker as possible) be Continued. After larval razorback sucker have been collected, the most efficient sampling method can be determined and monitoring protocol can be refined as necessary. [To date we have not been able to verify spawning by rawrback sucker, through the collection of their larvae, during 1998. However, there are a few individual larval catostomids from 1998 samples whose specific identifications have not yet been confirmed by Darrel E. Snyder, CSU Larval Fish Laboratory. We anticipate specific identification of those suckers prior to the end of the calendar year.] .;:.:; Obiectives: 1.) Determine the spawning periodicity of catostomids between mid-April-early June and examine potential correlations with temperature and discharge. 2.) Determine if reproduction by razorback sucker occurred in the San Juan River (upstream of Mexican Hat, UT) 3.) Provide comparative 'analysis of the reproductive effort of catostomids. 4.) Attempt to validate presumed spawning period of San Juan River catostomids using data from the razorback sucker and Colorado pikeminnow larval fish studies. Work Plan FY99.wpd 12 Budget and Work Plan FY99 . f";: ", , ' f.