Towards a Tropical Tuna Buoy-derived Abundance Index (TT-BAI)

Around the mid-2000s the tropical tuna purse seine fleet started to regularly use satellite linked echo-sounder buoys in their drifting FADs. This technological development is causing rapid changes in the fishing strategy and fleet behavior due to the possibility of informing remotely and in near real-time about the accurate geo-location of the FAD and the presence and size of tuna aggregations underneath them. Apart from its unquestionable utility as a fishery tool, echo-sounder buoys have also the potential of being a privileged observation platform to evaluate relative abundances of FAD-associated fish using catch-independent data. This paper discusses methodologies to account for covariates that are independent of abundance so that acoustic records derived from echo-sounder buoys can be used as a complementary relative abundance index in the stock assessment of tropical tuna stocks.