EFFECT OF THREADFIN SHAD DENSITY ON PRODUCTION OF THREADFIN SHAD AND GIZZARD SHAD LARVAE IN A TENNESSEE RESERVOIR

Production of larvae by threadfin shad, Dorosoma petenense, and gizzar d shad, D. cepedianum, varied over two orders of magnitude and was reg ulated by adult threadfin shad abundance over five years in Normandy R eservoir, Tennessee. Significantly more larvae of both species were pr oduced in years following winterkills of threadfin shad (repeated-meas ures ANOVA, df = 4, 75; F > 21.44, p = 0.0001). Peak geometric mean ca tch of threadfin shad larvae in neuston samples was inversely related to biomass (kg ha(-1); r = - 0.91; p = 0.031) and density (no. ha(-1); r = - 0.89; p = 0.043) of adult (> 70 mm total length) threadfin shad in mid-summer cove samples. Peak geometric mean catch of gizzard shad larvae was also inversely related to adult threadfin shad biomass (r = - 0.93; p = 0.022) and density (r = - 0.88; p = 0.046) in cove sampl es. Winterkills of threadfin shad were size selective, killing all fis h under 60 mm total length but allowing some unknown percentage of lar ger fish to survive. When threadfin shad stocks were reduced by winter kills, surviving threadfin shad and gizzard shad may have taken advant age of less competition for food resources in early spring and increas ed condition enough to spawn successfully.