A workshop was held to examine various issues that make the use of purse seine catch-per-unit-effort (CPUE) data in stock assessment difficult. The workshop convened a group of international experts from various fields who discussed possible ways to move forward in better understanding how and why purse seine CPUE may vary independent of stock abundance (or, equivalently, how fishing effort may vary independently of fishing mortality). The workshop carried out several preliminary analyses of the available data and made recommendations for future analyses. Recommendations were also made for the collection of information that may be available to industry but not to scientists. In terms of existing data, a number of analyses were recommended to better understand what makes catchability change over time (catchability is the constant of proportionality between stock abundance and CPUE). In addition, data mining of information about when fishing vessels began using various searching tools was viewed as potentially providing relevant information. Recommendations were made to make better use of the area searched during fishing operations, in addition to search time. In terms of future data collection possibilities, the workshop noted that access to information about the use of floating objects (including fish aggregating devices, FADs) for scientific purposes would likely provide useful insight into how to standardize such data with respect to covariates unrelated to fish abundance, and that FADs could potentially become observatories to monitor tuna densities. The Workshop also examined other potential alternatives to using CPUE, such as the biomass of tunas associated with FADs, and data derived from Vessel Monitoring Systems.
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