The impacts of stocking stress and largemouth bass predation on the survivorship of juvenile striped bass stocked in Smith Mountain Lake, Virginia
Smith Mountain Lake, Virginia supports a successful put-grow-take striped bass fishery. Empiric analysis of striped bass stocking has shown an inverse relationship between number of fingerling striped bass stocked and survival to age 1. Potential causes for this inverse relationship include largemouth bass predation on fingerling striped bass and mortality resulting from stocking stress.
Cage studies performed in 1994 and 1995 quantified percentage of fingerlings lost due to hauling/handling stress. Mean mortalities ranged from 1.78% for Phase I fingerlings in 1994 to 99.5% for Phase II fingerlings (reared in a recirculating aquaculture system for increased size at stocking) in 1994. Mortality rates varied greatly and were probably directly related to length of transport and inadequate thermal tempering prior to stocking. Highest mortality occurred at transport times in excess of six hours and when receiving water was 5° C warmer than transport water. A trial in which Phase I fingerlings were caged without transport or temperature change resulted in no mortality.
Predation mortality by largemouth bass was also considered as a source of poor first-year survival of striped bass in Penhook and Waterwheel stocking coves at Smith Mountain Lake. It was necessary to estimate largemouth bass population size, diet composition, and daily consumption (bioenergetic modeling) to determine the total number of striped bass lost to predation. Diet analysis revealed that age-0 striped bass made up a maximum of 2.5% of largemouth bass diets in the month following stocking; adult alewives constituted more than 60% by weight. The estimated number of striped bass lost was only 360 (0.1%) in 1994 and 3062 (1.2%) in 1995. Bioenergetic simulations demonstrated that predation could become significant in the unlikely event that the contribution of striped bass to largemouth diets increased to 10% or more. Based on results from diet analysis and a prey preference laboratory study, alewives appear to buffer predation of age-0 striped bass during the month after stocking. In 1994 and 1995, neither stocking stress associated with the typical Phase I fingerling stocking procedure nor largemouth bass predation resulted in substantial mortality of stocked fingerling striped bass.