Use of management strategy comparison scatterplots to identify clusters of high-performing strategies

A management simulation model was developed to test quota, trip limits and reduced longline hook numbers as alternatives to yearly seasonal (November) closure in South Australian snapper fisheries. Population dynamics equations and maximum-likelihood parameter estimates were supplied by an age- and length-based stock assessment model. The relative performance of tested management strategies was quantified by comparing change in egg production vs change in average catch, to optimise the trade-off between reproductive sustainability and catch foregone. Clusters of better-performing strategies were visually identifiable in management strategy scatterplots. These scatterplots display percentage change from the status quo in egg-production-per-female-recruit (y-axis) vs percentage change in catch-per-recruit (x-axis). Evaluated strategies fell into three distinct performance clusters. The best performing strategy extended November closure by 2 weeks. Strategies that retained the November closure performed uniformly better than those that removed it. Further simulation showed this resulted from non-closure strategies regulating only the commercial sector.