Size-dependent mechanisms influencing first-year growth and winter survival of stocked striped bass in a Virginia mainstream reservoir

To explain the limited stocking success of fingerling striped bass Morone s axatilis in Smith Mountain Lake, Virginia, we examined the relationship bet ween size-selective winter survival and length-dependent patterns in growth , food habits, prey fish availability, and lipid energy reserves during the first year of life in two successive years from 1994 to 1996. Length distr ibutions of striped bass were unimodal at the time of stocking, and growth remained positive for all fish during both growing seasons. By the fall of both years, a bimodal length distribution had developed within the age-0 co hort, which then consisted of small-mode (< 150 mm) and large-mode (> 180 m m) fish. The differential growth was attributed to size-dependent differenc es in prey consumption and diet quality. Small-mode striped bass: maintaine d a mixed diet of invertebrates and small cyprinids, whereas fish in the la rger mode were strictly piscivorous, consuming only age-0 alewives Alosa ps eudoharengus. The disparity in food habits, which was probably influenced b y the limited availability of alewife prey to smaller striped bass, resulte d in size-dependent differences in physiological condition, as larger juven iles amassed twice the lipid index levels as smaller fish by winter. By spr ing of both years, the bimodal length distribution had become unimodal and comprised almost entirely large-mode striped bass. In addition, large-mode fish had retained approximately 80% of their fall lipid stores, whereas sur viving small-mode individuals had retained only 40% of fall lipids. These r esults suggest that depletion of lipid energy, possibly coupled with other size-dependent stressors. may explain the greater winter mortality of small fish. Stocking fingerling striped bass in Smith Mountain Lake at a larger size and earlier in the growing season should result in a greater proportio n of stocked fish successfully switching to age-0 alewife prey, thereby imp roving first-year growth, winter survival, and recruitment to age 1.