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IOTC aims at maintaining stocks at levels not less than those capable of producing their maximum sustainable yield (MSY). For this, after the 2015 stock assessment of yellowfin, the Commission adopted a rebuilding plan towards improving the overall management of this fishery (Resolution 16-01, superseded by 17-01)1,2. The implemented measures include effort limitations and catch reductions for purse seine, gillnet and other gears starting in 2017. In particular, a catch reduction of 15% (relative to 2014) was adopted for purse seine fleets. These measures will be in force until they are reviewed no later than in 2019.
During the 2017 Scientific Committee (SC) meeting3 it was noted that Alternative Management Measures should be explored to improve the management of yellowfin tuna. This document discusses the potential of one alternative to the management measures currently in force for the purse seine fleets operating in the IOTC area of competence. In brief, we would like the Working Party on Tropical Tunas (WPTT) and SC to discuss the pros and cons of inputs controls (i.e. limiting the duration of the fishing season) in comparison to the output controls (i.e. current catch limits). The main reason for this is that the implementation of the catch limits for yellowfin in 2017 has been problematic. In the case of purse seiners, several problems have been identified. We list these and discuss their effects throughout this document. Some are general consequences of the application of catch based measures to multi-specific fisheries such as the Indian Ocean tropical tunas and some are derived from the dynamics of this fishery and the purse seine gear operations. We review the application of effort-based management in IATTC and WCPFC and add a series of projections to limit the fishing season to comply with the 15% catch reduction under Res 17-01. We also present a brief analysis of the seasonal trends of catch, effort and simulated temporal closures that would allow the rebuilding of yellowfin.
