Age-Specific Demography of Silver Carp: Implications for Management and Control

Silver carp (Hypophthalmichthys molitrix) were first introduced into the United States in the early 1980s and have since spread throughout the eastern United States including established populations throughout the Mississippi and Missouri River basins. The combination of rapid growth, quick maturation, and the ability to reproduce multiple times per year has allowed silver carp to expand their range and reach high population densities throughout many rivers in the Mississippi and Missouri River basins. Additionally, silver carp are capable of eating large quantities of plankton and detritus and may negatively impact native fishes in basins where they become established. We used published data on age-specific maturity, fecundity, and survival rates to model the population demography and the finite rate of population change for silver carp populations in large rivers in the Midwestern United States. Elasticity values obtained using an age-structured projection matrix based on a birth-pulse model were used to identify cohorts that management actions could target to have the greatest chance of reducing population abundance of this invasive species. Our models indicate that silver carp populations are projected to grow at a rate of 58% per year (λ=1.583). The population growth in our model was most sensitive to transition rates for growth and maturation of young fish (age-0 to age-2). Combined elasticity values for growth of young silver carp accounted for 56% of the total elasticity. Furthermore, when elasticity values for fecundity were incorporated, age-0 to age-2 silver carp account for 74% of the total elasticity. The results from our model indicate that efforts to minimize the impact of silver carp on native fishes should focus on younger fishes. Whereas most management efforts are currently focused on adult silver carp as a result of logistical constraints, our model indicates that the removal of younger fishes may better control the expansion of this prolific invasive species.