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EVALUATION OF STOCKING YEARLING LARGEMOUTH BASS IN CHATFIELD RESERVOIR, COLORADO DOUG KRIEGER COLORADO DIVISION OF WILDLIFE FORT COLLINS, COLORADO 80526 ABSTRACT Largemouth bass (Micropterus salmoides) were produced at the Wray Hatchery using intensive and extensive culture from 1979 to 1982. At 1 year of age the bass were sprayed with a fluores- cent pigment using compressed air and then stocked into Chat- field Reservoir, a 465-ha impoundment near Denver. Electro- fishing recoveries indicated that at 2 years of age, stocked bass comprised 12%, 59%, and 59% of all bass in their particu- lar year-class in 1979, 1980, and 1982, respectively. Growth of stocked bass was equal to, or greater than, natural bass, but mark retention may be low after the second year. During the next few years of the study, mark retention and the effects of stocking on the fishery will be evaluated. INTRODUCTION Interest in warmwater fishing, particularly for largemouth (Micropterus salmoides) and smallmouth (~. dolomeui) bass, has increased in Colorado to- gether with the Front Range population during the last few years. Although several Colorado reservoirs have, at times, had good bass populations, most larger reservoirs have had low densities of smaller bass. Biologists have blamed poor reproductive success, in part, for the lack of adequate recruit- ment. Therefore, in 1979 a stocking program was initiated on Chatfield Reservoir, a 465-ha flood control reservoir near Denver. Objectives of the study were to (1) define our capability for producing adequate numbers of yearling bass at our warmwater hatcheries, (2) determine the contribution of stocked bass to the populations, and (3) evaluate the effects of stock- ing on the fishery. METHODS Largemouth bass stocked as part of this evaluation were produced at the Division of Wildlife Wray Hatchery. until 1981, brood bass were trans- ferred from winter holding ponds to spawning ponds in late April. However, unsuccessful or multiple spawns resulted due to fluctuations in pond temper- ature caused by spring storms. Since 1981, brood bass were held in spring- fed concrete raceways until (1) pond temperatures were favorable (21-240C), (2) both sexes were sexually mature, and (3) extended weather forecast indi- cated fair weather. This method proved much more successful as nearly all 54