Evolution and current state of the technology of echo-sounder buoys used by Spanish tropical tuna purse seiners in the Atlantic, Indian and Pacific Oceans

• 99 interviews with Spanish fishers were conducted on the use of echo-sounder buoys.
• Number of DFADs equipped with echo-sounder buoys is rapidly increasing globally.
• DFAD fishing grounds are expanding thanks to the information provided by this tool.
• Some fishers are starting to remotely discriminate DFAD-associated fish.
• Effects of echo-sounder buoys on fleets strategy and efficiency are discussed.

Despite important technological changes in the tropical tuna purse seine fishery industry since the 1980s, the influence of these changes on the fleet efficiency and behaviour has not yet been investigated in depth. In this study, the practical use, fishing strategy and state of echo-sounder buoy technology applications were studied using personal interviews over three consecutive years (2010–2012) with approximately half of the Spanish tropical tuna purse seine fishing masters and licensed captains operating in the Atlantic, Pacific and Indian Oceans. The results suggested that echo-sounder buoys have significantly impacted drifting fish aggregating device (DFAD) fishing strategies since their introduction into the fishery in the last decade, favouring the expansion of DFAD fishing grounds. In addition, fishers are starting to be able to remotely discriminate species, which increases the fleet efficiency. Additionally, the number of echo-sounder buoys used by each vessel has been increasing each year, which demonstrates the utility of the information provided by this tool for the Spanish fleet. Various aspects of these devices’ use, consequences for fishing strategy, search time, nominal effort and potential future applications are discussed.