Food of blueback herring and threadfin shad in Jocassee Reservoir, South Carolina.
Threadfin shad (Dorosoma petenense) and blueback herring (Alosa aestivalis) were introduced into Jocassee Reservoir, South Carolina, USA in the early 1970s as prey for large piscivores. To assess the potential for trophic competition between these clupeids, their diets and the extent of diet overlap in May, August and December 1982 and February 1983 were studied. The diet of blueback herring consisted mainly of large species of cladocerans and copepods supplemented in August with Chaoborus punctipennis and young fish. Mean length of organisms eaten by blueback herring was 1.4 mm. Threadfin shad fed on smaller species of cladocerans and copepods, as well as on rotifers and copepod nauplii. Mean length of organisms eaten by threadfin shad was 0.4 mm, which differed significantly from the mean length of the zooplankton population in Jocassee Reservoir (0.6 mm). Phytoplankton contributed 24 and 32% of stomach contents of threadfin shad in August and December. Bosmina longirostris was important in the diet of both species, although blueback herring showed negative selection for it. Diet overlap between the clupeids was low on all 4 dates. There was no evidence of trophic competition between the 2 species in Jocassee Reservoir, but stocking them together is not recommended because both species are voracious planktivores and blueback herring are piscivorous.