Mechanisms Regulating Age-0 Gizzard Shad Dorosoma cepedianum Interactions with Age-0 Bluegill Lepomis macrochirus in Small Pond Experiments and a Public Fishing Lake

GENE W. KIM AND DENNIS R. DEVRIES, Department of Fisheries and Allied Aquacultures, 203 Swingle Hall, Auburn University, Alabama 36849, USA

JAY B. HAFFNER, Alabama Game and Fish, P.O. Box 305, Northport, Alabama 35476, USA

We are investigating the influence of larval gizzard shad Dorosoma cepedianum on larval bluegill Lepomis macrochirus, and indirectly on largemouth bass Micropterus salmoides in Southern waters. Our hypothesis is that competition by larval shad negatively affects larval bluegill survival, reducing age-0 bass survival through their first winter. To date we have conducted (1) a series of small pond experiments exploring competition between larval shad and bluegill, and (2) a study of larval dynamics in an intensively-managed fishing lake in Walker County, AL after removal of 36.9 lbs. of shad/acre. Preliminary results indicate that in Walker County Lake after shad removal, juvenile shad exhibited tremendous first-year growth relative to our ponds. Also, between systems, peak larval shad density did not exceed 10 fish/m³, versus 2-90 fish/m³ for larval bluegill. Rapid juvenile shad growth in Walker County Lake suggests that age-0 shad do not provide valuable forage for largemouth bass. The low larval shad abundance common to both systems, coupled with differential growth of juvenile shad between systems, is likely to affect competition among the species. Further analysis of the dynamics of this competition continues, including other sources of age-0 shad mortality.