Lac Seul, located in the English River watershed in northwestern Ontario, has been regulated for power production since 1935. The lake supports a sports and commercial fishery, with yellow pickerel (Stizostedion vitreum vitreum), northern pike (Esox lucius), lake whitefish (Coregonus clupeaformis), tullibee (Coregonus artedii), and coarse fish dominating the harvest. Commercial harvest records date to 1924, and sports anglers have been sampled on several occasions since 1960.An in depth analysis of water levels and fisheries productivity revealed a number of relationships. First, significant increases in the yields of yellow pickerel and northern pike were associated with the initial flooding. Second, changes in water level regulation patterns appear to have had short term negative impacts on productivity; however, the fishery has adapted to the new regimes with little long term effect. Third, correlations between annual fish yields and minimum spring water levels as well as seasonal water level variations suggest a threshold response of the fishery, below which water level changes have had little or no effect. The implications of these results to reservoir design and management are considered.
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