Self-starting CUSUM approach for monitoring data poor fisheries

This study attempts to determine whether a fish stock can be monitored and assessed if no historical fisheries data are available. Many existing methods require a time series of population and fishing pressure observations to estimate reference points to trigger decision rules. We demonstrate here the self-starting cumulative sum control chart (SS-CUSUM) where reference points are calibrated from indicator observations sequentially in real time as they are monitored. We used SS-CUSUM to monitor catch-based indicators from a simulated fishery where no previous scientific data are available. In the scenarios considered, the SS-CUSUM was successful in producing responses to fishing impacts with all indicators. A qualitative assessment on performance measures showed that the method worked best with indicators that represented the large fish component in landed catches (large fish indicators). Our study implies that neither a reference point nor a formal fish stock assessment is necessarily required to detect the impact of fishing on stock biomass. We discuss how SS-CUSUM could be incorporated into the assessment process for data poor fisheries.