EACH SPRING DURING ROTARY SCREW TRAP RST OPERATION ON THE TUOLUMNE RIVER, MIGRATING JUVENILE PACIFIC LAMPREY ENTOSPHENUS TRIDENTATUS MACROPTHALMIA ARE INCIDENTALLY CAPTURED DURING OUTMIGRATION MONITORING OF ANADROMOUS SALMONIDS. LITTLE IS KNOWN REGARDING PRODUCTION AND MIGRATION CHARACTERISTICS OF THIS SPECIES IN THE TUOLUMNE RIVER. RAW CATCH NUMBERS ARE USEFUL FOR CHARACTERIZING MIGRATION TIMING, BUT ARE OF LIMITED UTILITY FOR EVALUATING TRENDS IN ABUNDANCE. RAW CATCH CAN BE EXPANDED TO ESTIMATE ABUNDANCE, BUT REQUIRES AN ESTIMATE OF THE RST EFFICIENCY I.E., PROPORTION OF MIGRATING INDIVIDUALS CAPTURED IN THE RST. TRAP EFFICIENCY IS ESTIMATED USING MARKRECAPTURE METHODS AND IS OFTEN PERFORMED AS PART OF MONITORING JUVENILE SALMONIDS. HOWEVER, TRAP EFFICIENCY CAN CHANGE WITH RIVER CONDITIONS AND VARY BY LIFE STAGE. FURTHERMORE, EFFICIENCY IS SPECIFIC FOR A GIVEN TRAP. OUR GOALS ARE TO 1 IDENTIFY AN APPROPRIATE MARKING METHOD FOR JUVENILE LAMPREY, 2 PERFORM MULTIPLE RELEASES OF MARKED JUVENILES AT DIFFERENT FLOW CONDITIONS, AND 3 EVALUATE THE RELATIONSHIP BETWEEN TRAP EFFICIENCY AND FLOW CONDITIONS TO PERMIT ABUNDANCE ESTIMATION OF MIGRATING PACIFIC LAMPREY JUVENILES. A KEY FINDING FROM THIS WORK WILL BE THE EMPIRICAL RELATIONSHIP BETWEEN TRAP EFFICIENCY AND DISCHARGE, WHICH MAY THEN BE APPLIED TO PAST AND FUTURE CATCH DATA. ALTHOUGH THIS RELATIONSHIP WILL BE SPECIFIC TO THE TUOLUMNE RST, DEMONSTRATING AN EFFECTIVE METHOD FOR ESTIMATING LAMPREY EFFICIENCY CAN BE USED TO INCORPORATE LAMPREY MONITORING INTO EXISTING SALMONID RST MONITORING PROGRAMS. PROJECT DELIVERABLES WILL INCLUDE PRESENTATIONS TO MANAGERS AND A FINAL PROJECT REPORT IN MANUSCRIPT FORMAT SUITABLE FOR SUBMISSION TO A PEERREVIEWED PUBLICATION.