Effect of Water Level Fluctuations on Abundance of Young-of-year Largemouth Bass in a Hydropower Reservoir

Trends in the abundance of young-of-year largemouth bass (Micropterus salmoides) and water level fluctuations from 1976 to 1988 in Grand Lake were evaluated to assess recruitment strength before (1976-1981) and after (1982-1988) a change in reservoir operations. Significantly positive relationships between abundance of young-of- year largemouth bass and days of littoral flooding during spawning and nursery seasons, drawdown during revegetation season in the previous calendar year, combinations thereof, and water levels during these seasons indicated recruitment of largemouth bass was influenced by water level fluctuations. Implementation of a new operating rule curve in 1982 seemed to affect recruitment only indirectly by minimizing drawdown during late summer, thereby decreasing the exposure of shoreline areas of the reservoir for revegetation during the latter part of the growing season. A difference in mean elevation of about 1.2-1.5 m between revegetation and nursery seasons elicited favorable conditions for recruitment of largemouth bass in Grand Lake.

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