A preliminary analysis of the relationship between the number of FAD deployments and the number of FAD sets for the EPO purse-seine fishery

Limits on the numbers of fish-aggregating devices (FADs) and/or on the number of FAD sets, by vessel, are management options that have been proposed for, and in some cases implemented in, purse-seine fisheries that target tropical tunas associated with FADs. However, quantitative analyses supporting such management options are lacking. Therefore, two analyses of AIDCP observer data for Class-6 purse-seine vessels operating in the eastern Pacific Ocean (EPO) during 2012-2015 were conducted to provide information on fishing strategies of vessels making floating-object sets, and on the relationship between FAD deployments and floating-object sets. Different purse-seine vessel fishing strategies were identified using agglomerative hierarchical cluster analysis methods. The relationship between the number of FAD deployments and the number of floating-object sets were investigated with mixed-effects models. The cluster analysis results indicate vessel groups with the following fishing strategies: a tendency to make dolphin sets versus floating-object and unassociated sets; and, among vessels making floating-object sets, a tendency to make floating-objects sets on the vessel’s own FADs versus on objects found drifting and/or on FADs of unknown origin. Vessels fishing primarily on their own FADs tended to fish further offshore within the EPO than other vessels making floating-object sets and made a greater number of FAD deployments. The overall relationship between number of FAD deployments and number of floating-object sets is characterized by an increasing, nonlinear relationship that begins to asymptote at several hundred deployments. However, this nonlinear relationship differs between those vessels fishing primarily on their own FADs and those vessels making a greater proportion of their sets on other types of floating objects. These preliminary results highlight the complexity of FAD fishing in the EPO, which has implications regarding development of any management strategies that limit FAD usage, both in terms of the conservation of tunas and in terms of the economic performance of the different purse-seine fleet components operating in the EPO.