Long-term stocking success of largemouth bass and the relationship to natural populations

Despite the widespread use of supplemental stocking, survival of age-0 and age-1 stocked fish is often variable and stocking success is not commonly evaluated through adult size-classes. We evaluated the long-term contribution of stocked largemouth bass Micropterus salmoides from three annual stockings in 15 reservoirs in Illinois. Stocked largemouth bass were marked with fin clips and sampled for 5 years. Contribution of stocked fish to the population was highest for age-0 (21%) and age-1 largemouth bass (17%) but decreased significantly in adult fish (5%). Contribution of stocked bass was not associated with either populations of wild largemouth bass or latitude. Survival of stocked fish was similar to survival of wild fish through age 1. Age-0 abundance of wild and stocked largemouth bass were positively correlated in the fall following stocking, suggesting that similar factors may influence initial survival. Survival of stocked fish from age-l to adult age decreased significantly compared to wild fish, resulting in low contribution of stocked bass to the adult population. Adult and age-1 catch per unit effort of stocked largemouth bass were positively correlated with the mean size of stocked bass in the first fall after stocking and the following spring, indicating that lakes with higher growth rates have increased contribution of stocked fish. We found limited contribution of stocked fish to adult largemouth bass populations due to low survival from age-1 to adult age. Assessments of fish stocking success should evaluate survival of stocked fish through adult ages or they may omit a critical period for mortality.