Improving on deck best handling and release practices for sharks in tuna purse seiners using hopper with ramp devices

Murua J, Ferarios JM, Grande M, Santiago J (2021) Improving on deck best handling and release practices for sharks in tuna purse seiners using hopper with ramp devices. In: WCPFC Scientific Committee 17th Regular Session. WCPFC-SC17-2021/EB-IP-13, Electronic Meeting

A possible bycatch reduction device (BRD) that tuna purse seiners could employ to promote safer and faster release of vulnerable bycatch, such as sharks, are hoppers with ramps. These selective hopper trays can take many shapes and sizes depending on the vessels’ top deck configuration. Not all hoppers are equally valuable for bycatch release as some are either too small to access the bycatch or act as funnels with no stop mechanism to allow for time to detect and take out non-target species. In this study four class A purse seiners operating in the Pacific Ocean and fitted with mobile hoppers were examined for shark release efficiency. Observer data results indicated that when hoppers were used on the vessels between 92% and 98% of the sharks were released from the top deck, against 21% to 46% with no hopper. Hoppers can increase shark survival because their mortality greatly increases once they reach the lower deck, where release times are delayed if there is no release exit from this area, resulting in sharks having to be carried manually upstairs. In addition, release ramps were built and trialled with the hoppers, which acted as wet slides to facilitate faster and safer release of sharks and other bycatches with minimal handling. While designs of hopper and ramps for bycatch release can still be improved, they offer a promising tool for fleets to implement best release practices of vulnerable species. Future trials will employ satellite pop-up tags to properly assess survival rates with and without hoppers. We recommend that tuna RFMOs concerned with best bycatch mitigation and crew safety practices consider the implementation of hoppers with ramps as an efficient BRD in tropical tuna purse seiners which would be in line with shark protection recommendations in CMM-2019-04 paragraph 17.