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Job Progress Report State: Colorado Project No. : 7400/ENDG 0700 Name: Aquatic Nongame Research Study No. : SE-3-l4 Title: Endangered Fishes Investigations Period Covered: November 1, 1989 - October 31, 1990 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 The introduction of non-native fish species in rivers of the Upper Colorado River Basin is considered one of the primary contributing factors toward the decline and endangered status of the Colorado squawfish (Ptychocheilus lucius), humpback chub (Gila cypha), bony tail (Gila elegans), and razorback sucker (Xyrauchen texanus). Gamefish species such as northern pike (Esox lucius), channel catfish (Ictalurus punctatus), and largemouth bass (Micropterus salmoides) are implicated as part of the exotic fish problem due to their predatory nature, but field evidence documenting their presumed negative impacts are lacking. Any future management plans to reduce populations of these gamefish species to benefit the endangered species, however, will pose added difficulties due to their popularity with the angling public. This study's primary focus is to determine life history patterns and requirements of warmwater gamefish species in Upper Basin Rivers from the perspective of how well these populations are adapting to the riverine environment, and to compare and contrast seasonal habitat use and prey selection between the endangered and non-native fishes for evidence of potential impacts from predation and competition. Knowledge of limitations imposed on these gamefish species and other introduced, non-native fish species by a xeric riverine environment will help define the problems posed by these species on the native fishes, and may also indicate recovery measures necessary to minimize negative interactions with the endangered species. The 1990 segment narrative detailing objectives and work schedules listed seven jobs. An eighth job was added in August 1990 concerning Colorado squawfish age and growth. This job was funded through a 100% grant from the U.S. Fish and Wildlife Service, Region 6, with cnow serving as contract supervisor. A memorandum of understanding (MOU) was created between cnow and the Larval Fish Laboratory at Colorado State University to perform the planned studies. Job titles and objectives were: 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- salmonid gamefish populations in Upper Basin rivers in Colorado.