Testing bycatch release devices for vulnerable elasmobranch species in tropical tuna purse seiners of the eastern Pacific Ocean

Several regulations on handling and releasing practices have been adopted in the past by IATTC to protect marine megafauna bycatch species such as sea turtles, sharks, mobulid rays, and marine mammals. However, in purse seiners some of these practices, especially regarding elasmobranchs, are mostly manual and still very rudimentary. When large individuals or dangerous species arrive on deck, manual manipulation entails difficulties and risks for crew members, which can deter release actions and delay the release of vulnerable species. This delay negatively affects post-release survival rates of marine megafauna by elevating the animals’ stress levels and chances of suffocation. In recent years some bycatch release device (BRD) prototypes have been developed, or redesigned, and tested by the Spanish fleet in the Atlantic and Indian Oceans. In 2021, the IATTC, ISSF and AZTI signed a Memorandum of Understanding to trial novel release equipment on several OPAGAC vessels operating in the eastern Pacific Ocean (EPO) with the goal of examining their efficiency for improving fishers’ safety and elasmobranch post-release survival. Several EPO and western and central Pacific Ocean (WCPO) opportunistic research cruises are ongoing with trained scientists and observers onboard to satellite tag and take condition measures (e.g., vitality indexes, blood lactate levels) to estimate post-release mortality of mobulids and sharks released with different devices and methods. These studies can help document survival rates of vulnerable species released with BRDs and provide information for fisheries management on better options to improve current bycatch handling and release practice guidelines in tuna purse seiners.