Steve M. Sammons and Phillip W. Bettoli, Tennessee Cooperative Fishery Research Unit, Tennessee Technological University, Box 5114, Cookeville, TN 38505

Abstract. Larval production by threadfin shad Dorosoma petenense and gizzard shad D. cepedianum varied over two orders of magnitude and was regulated by adult threadfin shad abundance over five years in Normandy Reservoir, Tennessee. Significantly more larvae of both species were produced in years following winterkills of threadfin shad (repeated-measures ANOVA, df = 4, 75; F > 21.44, P = 0.0001). Peak geometric mean catch of larval threadfin shad in neuston samples was inversely related to biomass of adult (>70 mm total length) threadfin shad in mid-summer cove samples (r = -0.91; P = 0.031). Peak geometric mean catch of larval gizzard shad was also inversely related to adult threadfin shad biomass in cove samples (r = -0.93; P = 0.022). Winterkills of threadfin shad were size selective, killing all fish under 60 mm total length but allowing some unknown percentage of larger fish to survive. When threadfin shad populations were reduced by winterkills, gizzard shad and surviving threadfin shad may have taken advantage of less competition for food resources in early spring and increased condition enough to spawn successfully.