Towards acoustic discrimination of tuna species at FADs

Purse seine fishers targeting tropical tuna use geo-locating buoys to track Fish Aggregating Devices (FADs). Many of these buoys are now equipped with echo-sounders in order to provide remote information on the aggregated biomass. Nowadays these biomass estimates are not accurate enough to provide information on species composition. We investigate tuna species discrimination at FADs to provide in situ and remote species composition, by using 3 echo-sounders operating simultaneously at 3 different frequencies (38 kHz, 120 kHz and 200 kHz). Preliminary target strength (TS) for Skipjack tunas were obtained for the different frequencies used and a frequency response mask investigated to discriminate between species. This work has confirmed the potential of using multiple frequencies to discriminate between fish with swim-bladder (Yellowfin and Bigeye tunas) from fish without swim-bladder (Skipjack). We discuss the potential of acoustics for both, to mitigate by-catch and undesirable sizes of tuna species and to improve our knowledge on the ecology and abundance of tunas.