"Effects of Underestimating Catch and Effort On Surplus Production Models"

Stocks are often regulated based on surplus production models when only catch and effort (or CPUE) data are available. However, reported catch, effort and CPUE rarely reflect the true values. We studied effects of underestimated catch and effort on surplus production model parameters (e.g., MSY, B_MSY, F_MSY, B_current, F_current) as well as key ratios of parameters. We used ASPIC software to examine the effects of adding catch and effort to the nominal data from two managed fisheries, northern pike in Minnesota and queen conch in Turks and Caicos Islands. The scenarios suggest that if both catch and effort are underestimated, MSY, B_MSY, k, and biomass are also underestimated, but F_MSY, F_current/F_MSY and catch/MSY generally remain the same in the original and altered scenarios. The biases in parameter estimates are robust to changes over time in the magnitude of underreporting, but eventually continued growth in underreporting will cause problems particularly with F_current/F_MSY. Independent population estimates can be incorporated into a production model, and can help mitigate errors in catch and effort, but the position of the population estimates in the time series is important. This study has resolved issues that arose in the management of two fisheries.