Application of an age-structured population model of bluegill sunfish (Lepomis macrochirus)

: Implications for the control measures in Japan

Abstract

Evaluating the effectiveness of control measures provides helpful information for invasive species management. Here, we evaluated the impacts of removal rates of eggs, juvenile fish, and adult fish on the equilibrium abundance of bluegill sunfish (Lepomis macrochiru), by using an age-structured population model developed in the Hyco Reservoir (North Carolina, USA). When controlling eggs, juveniles, and adults independently, removal rates of 0. 84-0. 92 were necessary to eradicate the bluegill population (i.e., the equilibrium abundance < 1 individual). Given the constant removal of eggs, additional efforts to control juvenile or adult abundance could lead to the population extinction with smaller removal rates, compared with controlling them independently. Furthermore, inverse U-shape responses of the equilibrium abundance to independent removals of eggs and adults were observed; the bluegill abundance increased until the removal rates increased to approximately 0. 8 and 0. 6, respectively. This is because the population model used here employs the Ricker-type density dependence to model the relationship between the number of eggs and age-0 fish abundance. This result suggests the importance to estimate and consider the densitydependence effects in the actual managements. Although the application of our results to practical managements of bluegills in Japan requires further consideration, as illustrated here, the use of population model can estimate and compare the impacts of control measures, and help to select better strategies.