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reached. Their suggestion is corroborated by the observations of Oliver et ale (1979) and the model of Shuter et ale (1980) which illustrate that small- mouth bass must reach a critical size by the end of their first growing sea- son in order to survive the subsequent winter. The northerly limit of the distribution of both largemouth and small- mouth bass can be related to agricultural growing season or frost free days. Observation of the native ranges of both species (Robbins and MacCrimmon 1974) and the average length of the growing season across the northern por- tions of the United States (Lowers 1960) shows the northern edge of their native ranges to correspond closely with an average growing season of 120 days. As a result of human intervention both species have been spread north- ward and have become naturalized in areas with shorter growing seasons. Smallmouth bass now support Canadian sport fisheries in areas with 95-100 frost free days, while largemouth bass occur in areas with 100-110 day grow- ing seasons. LIMITS TO WYOMING DISTRIBUTION If a 100 day growing season is considered the minimum at which large- mouth and smallmouth bass can become naturalized their potential distribu- tion in Wyoming impoundments can be estimated. Data on the mean length of the growing season, altitude, and latitude of 42 scattered locations across Wyoming were assessed. A curvilinear relation between growing season and altitude was observed (Figure 1). Evaluation of this relation between alti- tude and growing season using multiple regression analysis indicated that 62% of the variability in length of growing season could be accounted for from knowledge of altitude. Addition of latitude as a variable did not sig- nificantly increase the variance accounted for by the regression. Figure 1 suggests that a 100 day or longer growing season occurs at altitudes less than 1900m (6200 ft.). Thus, the distribution of black bass in Wyoming would be expected to be limited to altitudes less than 1900m (6200 ft.). Shuter et ale (1980) showed that the mean July air temperature influ- ences first year survival of smallmouth bass. Mean July air temperatures for 33 locations in Wyoming were plotted against altitude (Figure 2). Eval- uation of the curvilinear relation showed that 68% of the variability in mean July air temperature was accounted for from knowledge of altitude. Knowledge of latitude did not significantly increase the variance accounted for by the regression. Using the model of Shuter et ale (1980) that relates mean July air temperature to the overwinter survival of young-of-year smal1- mouth bass, it is predicted that at altitudes greater than 1900m (6200 ft.) the mean survival over winter would be between 0.0 and 0.5. At altitudes below 1900m (6200 ft.), mean survival would be expected to be between 0.9 and 1.0. These relations between overwinter survival of young-of-year fish and altitude again suggest that the distribution of black bass in Wyoming should be limited to altitudes less than 1900m (6200 ft.). Data on the known distribution of largemouth bass and smallmouth bass were obtained from the Wyoming Game and Fish Department. Records of large- mouth bass in 164 impoundments and smallmouth bass in 8 impoundments were found. A check of the altitude at which the impoundments were located showed four largemouth bass populations above 1900m (6200 ft.) and three at II]