Abstract
Most of the drifting fish aggregating devices (DFADs) used in industrial tropical tuna purse seine fisheries are equipped with satellite linked echosounder buoys, which provide fishing crews with remote, accurate geolocation information and rough estimates of FAD-associated tuna biomass. One of the most common brands of echosounder buoys (SATLINK, Madrid, Spain) is currently calibrated for the target strength of skipjack tuna (Katsuwonus pelamis) and provides biomass data on. that species. Using that brand of echosounder buoy, we developed a new behavior-based approach to provide relative biomass estimates and a remote target classification of fish aggregations at FADs. The model is based on current knowledge of the vertical distribution of the main fish species associated with FADs, as well as on appropriate TS and weight values for different species and sizes, and is further based on parameter optimization against a set of fishing operations on DFADs. This model reduced the error variability in biomass estimates by about 60% and also reduced the ranges of underestimation. and overestimation by 55% and 75%, respectively. Similarly, the original coefficients of correlation and determination were also considerably improved from 0.50 and 0.25 to 0.90 and 0.82, respectively. We discuss how this new method opens new opportunities for scientific studies and has implications for sustainable fishing.