Use of electronic monitoring systems to optimize observer sampling protocols onboard French purse seiners of the Indian Ocean

Observer programs on tuna purse seine vessels are essential to collect information on bycatch and discards in order to monitor the impact of fisheries on populations and ecosystems. On-board observers estimate discards following a sampling protocol and sometimes extrapolation methods (based on the number of brailers or time) when counting exhaustively is not possible. However, these methods may be biased because brailers have different filling rates, which in turns results in a heterogeneous flow of discarded individuals during the sorting process, and may lead to biased estimates. Electronic Monitoring Systems (EMS) have been implemented since 2013 on French purse seiners to complement on-board observer programs on vessels that cannot embark observers. On-board cameras allow monitoring sorting operations continuously and monitoring the discard flow in time and space (upper vs lower deck). In this study, we used EMS « counts per minute » of discards from 5 vessels operating in the Indian Ocean to describe the general trends in sorting flow on the upper and lower decks.