Ecology and behavior of tuna and non-tuna species at drifting fish aggregating devices (DFADs) in the Indian Ocean using fishers'echo-sounder buoys.

Abstract

Around 65% of tuna purse seine landings are taken using drifting Fish Aggregating Devices (DFADs). DFADs, constructed and deployed by fishers to increase their catches, aggregate the three main tropical tuna species, together with some non-target species. Tropical tuna purse seiner fisheries have increased the use of DFADs in the last 20 years, generating a need for knowledge on DFADs fisheries which has not improved at the same pace as its use. Understanding their impacts on the ecosystem and the ecology and behavior of marine species associated with floating objects, with the aim of providing the best scientific advice in support of the management of tropical tuna species is, thus, needed. However, studies related to DFADs are quite limited, due basically to the great economic and human cost involved in the research of the drifting objects, as they are very temporary in time and space. Currently, DFADs are equipped with satellite linked echo-sounder buoys, which are continuously streaming information about the rough estimate of the biomass of tuna and non-tuna aggregations under the DFADs along its trajectory, almost in real time representing a powerful tool for the study of pelagic ecosystems. This thesis presents scientific research results about the aggregation process, spatio-temporal distribution and environmental preferences of species associated with DFADs in the Indian Ocean using acoustic data provided by fishers¿ echo-sounder buoys. These findings represent a significant advance in the understanding of ecology and behavior of species associated to DFADs and have important implications for the definition of more efficient management approaches of its fishery.