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Acoustic Discrimination Exploring Technology to Support Selective Fishing Published October 2022 Acoustic Data Can Help Fishers Identify Species at FADs Tuna fishers use buoys equipped with echosounders to remotely track their FADs in the ocean. They plan fishing trips based on the buoys’ acoustic estimate of the amount of fish aggregated at FADs. But current technology does not allow for discriminating species or sizes, which means fishers may spend time and resources traveling to areas where the FADs have attracted other species or sizes they were not targeting for their catch. Target Outcome: Knowing which species are at FADs can help a vessel’s crew focus most on the FADs that are attracting a higher proportion of the target tuna species. This approach can reduce overfishing and bycatch — and also save fuel and reduce emissions from fishing operations. One current challenge to fishing selectively is that FADs can attract a mix of tuna and other marine species as well as fish of different sizes, making it difficult to catch only the tuna species that are being targeted. FAD tracking buoys with echosounders emit sound pulses that reflect off underwater targets like fish. Fishers rely on echosounder data to know the amount of fish that are aggregating at FADs. Each species sends a different sound response back to echosounders — and has a distinctive acoustic signature. As of 2022, after years of research, scientists have “decoded” the individual acoustic signatures of skipjack, bigeye, and yellowfin. These three species have contrasting frequency responses. Species Reflect Sound Differently Skipjack, bigeye, and yellowfin are the main tropical tuna species found at FADs. Depending on the ocean region, certain species may be suffering from overfishing. Ideally, before they make a set, fishers could target the tuna species whose stocks are at healthy levels. The process of using echosounders to identify and differentiate species is called “acoustic discrimination.” Tuna species produce different acoustic signatures based on the presence/sizeor absence of a swim bladder. Swim bladder: an air-filled sac that functions as a ballast organ, enabling the fish to maintain its swim depth without floating upward or sinking. Fish with a swim bladder, like bigeye and yellowfin tuna, reflect more sound. Fish without a swim bladder, like skipjack tuna, reflect less sound. Acoustic Discrimination Timeline Through at-sea research, ISSF scientists have been studying the acoustic responses and behavior of tuna and other species in purse-seine fisheries. Our findings may enable tuna fishers to use echosounders and other acoustic equipment to better identify the species, size, and number of tuna and non-tuna at fish aggregating devices (FADs) before they cast their nets — helping to avoid overfishing and reduce bycatch. ISSF acoustic-discrimination research has been funded by the FAO GEF Common Oceans ABNJ Tuna Project, the Basque government, and NOAA fisheries.