A DETERMINISTIC MODEL OF THE RESPONSE OF THREADFIN SHAD TO AQUATIC MACROPHYTE CONTROL

A computer simulation model was developed to investigate the relationships between aquatic macrophytes, chlorophyll-a, and threadfin shad (Dorosoma petenense) abundance in Lake Conroe, Texas. Areal coverage of vegetation was used as a driving variable in the model to regulate algal biomass in the limnetic zone, larval shad survival, and adult reproductive fitness. Empirical data used in model development were collected before and after grass carp Ctenopharyngodon idella were stocked in 1981-1982 to control over 3,500 hectares of submersed vegetation. Complete vegetation control by 1983 resulted in increased chlorophyll-a concentrations in the limnetic zone and increased threadfin shad abundance. The model plausibly accounted for the positive response by the shad population but responded slower than the real system to macrophyte removal. Sensitivity analysis revealed the model was most sensitive to larval mortality rates and the functional form of the relationship between macrophyte abundance and chlorophyll-a concentrations.