Effects of Gizzard Shad and Threadfin Shad on Zooplankton and Young-of-Year White Crappie Production

Abstract

We examined the effects of gizzard shad Dorosoma cepedianum and threadfin shad Dorosoma petenense on zooplankton abundance and on reproduction by white crappie Pomoxis annularis in a March–July 1986 Texas pond experiment of factorial design. We used four treatment combinations: no shad, gizzard shad, threadfin shad, and gizzard shad + threadfin shad. Densities of cyclopoid copepodids and Daphnia sp. were suppressed in the presence of threadfin shad but not gizzard shad. The presence of gizzard shad or threadfin shad was associated with decreased total number and biomass of young-of-year white crappies, a shift in white crappie size distributions toward larger individuals, and increased mean weight of white crappies in some size-classes. The biomass of young-of-year gizzard shad decreased in the presence of threadfin shad. Our study suggests that gizzard shad and threadfin shad may decrease the density and biomass of young-of-year white crappies, but increase their mean size.