Temperature,plankton and conspecific density influence dynamics of age‐0 gizzard shad: implications for a gape‐limited piscivore

Age‐0 gizzard shad Dorosoma cepedianum are the main prey fish for white crappies Pomoxis annularis in many US reservoirs. However, these prey fish commonly outgrow their vulnerability to white crappie predation in some, but not all, northern Missouri reservoirs. Potential variables that could influence abundance, growth and mortality of age‐0 gizzard shad were examined in three reservoirs that differed with respect to age‐0 gizzard shad growth rates. Because of thermal effluent from a power plant, gizzard shad spawned earlier in Thomas Hill Lake and initial densities of larvae were greater than in the other reservoirs. Larval and juvenile gizzard shad grew slowest in Thomas Hill Lake, followed by Mark Twain Lake and Long Branch Lake. Growth rate of larvae increased with increasing water temperature and food abundance, but decreased with increasing conspecific density. Similar relationships were found for juvenile growth, except that growth declined with increasing temperature. The slower growth of larvae and juveniles in Thomas Hill Lake was probably a consequence of their greater densities relative to their food abundance and higher water temperatures during the juvenile stage. Conversely, both larvae and juvenile gizzard shad grew more rapidly and juveniles attained large sizes in Long Branch Lake owing to their lower densities relative to their available food. Mortality of larvae and juveniles was mostly similar among the reservoirs. Because of their greater abundance and slower growth, gizzard shad were available as prey for white crappies for a longer period in Thomas Hill Lake than in the other reservoirs.