SIMULATING SMALLMOUTH BASS REPRODUCTIVE SUCCESS IN RESERVOIRS SUBJECTTO WATER-LEVEL FLUCTUATIONS

An individual-based model of nesting smallmouth bass, Micropterus dolo mieu, is used to predict the effects of water level fluctuations on re productive success. The model simulates daily nest site selection, spa wning, nest guarding, and development and survival of eggs, embryos, a nd larvae until dispersal. The model was configured for Brownlee Reser voir, Idaho-Oregon. Each reservoir bank is represented as a rectangula r grid of cells, with each cell characterized by an assigned slope, su bstrate, and elevation, and by a water depth that varied daily. Nest s ite (cell) selection is determined from a habitat suitability index (H SI) based on substrate, slope, and depth. Development of young is temp erature-dependent. Mortality of young occurs via attrition, abandonmen t by the guarding male, and probabilistic whole-nest catastrophe. Simu lations were performed that used observed data for 1991 to 1996. Model predicted nest habitat selection and egg-to-dispersal survival rates were similar to observed values. Additional model simulations showed t hat: (1) nest habitat selection was best predicted when depth, slope, and substrate were considered together rather than singly, (2) egg-to- dispersal survival was related to the magnitude of water level fluctua tions during the peak spawning period, (3) relating mortality to HSI v alues resulted in lower survival, while relating growth to HSI values resulted in higher survival, and (4) spawning habitat is not limiting in Brownlee Reservoir. Suggestions for future monitoring of reservoir- based smallmouth bass populations are discussed.