Responses to Gizzard Shad Recovery following Selective Treatment in Walker County Lake, Alabama, 1996-1999

Abstract

Gizzard shad Dorosoma cepedianum is an important prey fish that is capable of influencing both the upper and lower trophic levels in aquatic systems. Contrary to our predictions, during the 4 years after a selective reduction of gizzard shad in Walker County State Fishing Lake (WCL), Alabama, the sport fish population structure did not decline as gizzard shad abundance rebounded. Adult gizzard shad catch rates in electrofishing transects (g/h) increased annually, and we saw a concomitant reduction of the WCL zooplankton community over the 4-year period. Limnetic larval gizzard shad density was highest in the second postreduction year and declined during the third and fourth years. In years when larval gizzard shad appeared in limnetic larval fish samples before larval white crappies Pomoxis annularis, larval white crappie densities were low. Conversely, the density of limnetic larval sunfishes Lepomis spp. was unrelated to that of larval gizzard shad, probably because of the protracted reproduction periods of the sunfishes. The combination of the density-dependent growth of juvenile gizzard shad and continual production of age-0 sunfishes provided abundant prey for largemouth bass Micropterus salmoides. Consequently, both the electrofishing catch rates and relative weights of largemouth bass remained high throughout the 4-year postreduction period, contrary to the a priori expectations that prompted the reduction. Although gizzard shad biomass increased markedly during the recovery period, a decline in the sport fishery was not apparent within the 4-year period of this study. Our findings suggest that the interval between treatments to reduce the gizzard shad population in WCL may be increased to more than 3 years, potentially saving time and personnel costs and providing an opportunity for positive public relations with respect to fish management in such a system.