Carcharhinus falciformis - a massive bycatch in the industrial purse seine industry but systematically underreported and deprived of any protection in the Indian Ocean
Carcharhinus falciformis is known to be the most significant bycatch species in purse sein tuna fisheries especially when setting on drifting FADs, the increasingly applied practice by large tuna fleets in the Indian Ocean. However, the magnitude of impact of this practice on the Indian Ocean stock of silky sharks continues to be considered as very low whilst longlining and gillnetting are quoted to be the main contributors to the overall annual catch of silky sharks at IOTC (Garcia and Herrera, 2018). However, considering the poor compliance with reporting requirements for sharks in line with Resolution 17/05 huge doubts remain on both, the overall fishery related mortality of this IUCN listed vulnerable species and in particular the contribution of discards from purse seine fleets to this overall mortality. By combining data reported by CPCs to the IOTC Secretariat with fishery specific data disclosed by fisheries as part of their MSC certification the cumulative impact of purse seine fisheries on silky sharks in the Indian Ocean can be assessed more adequately. This paper presents a first, preliminary assessment and results in a quite different estimate about the magnitude of impact this fishing practice has on silky sharks, contradicting the assumption of the negligible impact of purse seining on silky shark mortality. With close to 1,000 tonnes of cumulated annual discards or more than 50,000 animals reported by the 28 vessels of the three currently MSC certified fleets alone, the total annual dimension of discards from large purse seine vessels in the Indian Ocean may easily be two to three times higher than these numbers without even considering any retained bycatch or discards by the large number of small purse seine vessels operated for example by the Indonesian fleet. The extent of discards of possibly 2,000 tonnes or more and the resulting total silky shark mortality is therefore at least ten times higher than previously assumed, while industry continues to claim that purse seine fleets are only responsible for a very small percentage of 1.3% (Garcia & Herrera 2018) of the total fishing induced mortality of silky sharks in the Indian Ocean. In conclusion this bycatch level should no longer be ignored especially in view of the large overall percentage of tuna caught by large purse seiners setting on dFADs in the Indian Ocean. The situation certainly requires both, substantially improved and enforced reporting requirements for bycatch and discards and the improved granularity by providing these reports at the level of the individual vessel, as well as the introduction of more effective bycatch avoidance measures. While bycatch mitigation measures reducing on board mortality and increasing post release survival certainly remain important and should be further improved, these alone should not be considered as sufficient to address the overall problem. Especially in view of the widespread lack or inadequate application of existing technical measures and best practices by most fleets and the high vulnerability of juvenile silky sharks, making up for the majority of the bycatch, effective bycatch avoidance and fully transparent reporting of all interactions at vessel level must be made a priority.