Responses of gizzard shad and white crappie to introductions of palmetto bass

Abstract

Palmetto bass (female striped bass Morone saxatilis × male white bass Morone chrysops) were stocked into Long Branch Lake, Missouri, USA in an effort to restructure the gizzard shad Dorosoma cepedianum population via predation. The goal of this restructuring was to provide more suitable-size prey for white crappie Pomoxis annularis, thereby improving growth of this important sport fish. Secondarily, palmetto bass may prey on the abundant white crappie population which may reduce density-dependent effects on growth. Trends in abundance and mean total length (TL) at age of white crappie and gizzard shad were examined over an eight-year period which spanned years before, during, and after stocking of palmetto bass. Also, trends in water quality and zooplankton variables, which may influence gizzard shad demographics, were examined during this period. Following stockings of palmetto bass, mean TL at age of adults and abundance of age-0 gizzard shad increased. Water quality variables and zooplankton biomass that may have influenced gizzard shad showed no temporal trends except for turbidity which increased over time. Despite the changes in the gizzard shad population, mean TL at age of white crappie did not improve and their abundance did not decline. Age-0 gizzard shad still quickly outgrew their vulnerability to most white crappie. It may be necessary to incorporate other management strategies in addition to stocking palmetto bass to improve growth of white crappie in this reservoir.