Sensitivity Of Yield-Per-Recruit And Spawning-Biomass-Per-Recruit Models To Bias And Imprecision In Life History Parameters: An Example Based On Life History Parameters Of Japanese Eel (Anguilla Japonica)

Yield-per-recruit and spawning-biomass-per-recruit models, are commonly used for evaluating the status of a fishery. In practice, model parameters are themselves usually estimates that are subject to both bias (uncertainty in the mean) and imprecision (uncertainty in the standard deviation). Using Monte Carlo simulation with data for female Japanese eel (Anguilla japonica) from the Kao-Ping River in Taiwan, we examined the sensitivity of such models to different degrees of bias and imprecision in the life history parameters. Positive biases in natural mortality and the von Bertalanffy growth coefficient led to larger relative changes in the mean and standard deviation of estimated fishing-mortality based biological reference points (F-BRPs) than did changes under negative biases. Higher degrees of imprecision in parameters did not affect the means of F-BRPs, but their standard deviations increased. Composite risks of overfishing depended mainly on the changes in the means of F-BRPs rather than on their standard deviations. Therefore, reducing the biases in key life history parameters, as well as the bias and imprecision in the current rate of fishing mortality, may be the most relevant approach for obtaining correct estimates of the risks of overfishing.