Includes bibliographical references (page 18).

Abstract -- Introduction -- Factors compared with year-class strength fluctuations -- Prediction of future production -- Summary -- Literature cited -- Appendix A -- Water levels and air temperature data on Yellowstone Lake -- Appendix B -- Computation of residuals -- Appendix C -- Adjusted estimates of Pelican Creek year-class strength -- Appendix D -- Relative year-class strength of Pelican Creek and Fishing Bridge catch Fluctuations in strength of year classes from 1945 to 1956 of Yellowstone Lake cutthroat from Pelican and Chipmunk Creeks are compared with the parental stock and several climatically influenced factors of the environment. Variations in year-class strength in the two tributaries were highly correlated with fluctuations in lake water levels. Strong year classes occurred in yeas of low water. Female spawner escapement, timing of the runs, and summer air temperatures were not significant factors. A formula based on water levels is presented for predicting year-class strength in Pelican Creek and in the Fishing Bridge area fishery. Stocking of fry in years of high water is suggested as a means of supplementing natural production. A method of forecasting lake water levels several months in advance of their occurrence is discussed.