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State: Colorado Project No.: 7400/ENDG 0700 Name: Aquatic Nongame Research , Study No.: SE-3-l6 Title: Endangered Fishes Investigations Period Covered: July 1, 1991 - October 31, 1992 Study Objective: To determine the impact of non-native, warmwater gamefish species via predation and competition upon Upper Colorado River Basin endangered fish species. INTRODUCTION This project was amended in 1991 to include an additional field season for data collection on three specific aspects of Jobs 1-3. Work to be accomplished was defined in three tasks: Task 1: Continue experimental treatment in spring backwaters in Yampa River by pike removal to assess response by associated species. Task 2: Continue attempts at field confirmation of predation on Colorado squawfish larvae (or Razorback sucker larvae) or YOY by select species using recent lab results from the CSU Larval Fish Lab as guidance. Task 3: Continue analysis of fish prey selection by northern pike and channel catfish, and expand to correlate predator gape characteristics to predation vulnerability in existing size structure of adult Colorado squawfish population. In addition to standardized monitoring, the Northwest Regional Office carried on two additional jobs concerning razorback sucker distribution inventory in the Colorado River above Palisade (Job 7), and an evaluation of Colorado squawfish stocked in Kenney Reservoir (Job 8). Progress on these Jobs is also reported here. Job Objectives: Job 1. Title: Gamefish species life history data Objective: To determine 3-year trends in abundance, distribution, reproductive success, and size structure of non-native, non-sa1monid gamefish populations in Uppe~ Basin rivers in Colorado. Job 2. Title: Gamefish predation upon endangered fishes Objective: To determine the incidence of predation by non-native, non-salmonid gamefish species upon the endangered fishes.