Using effort control measures to implement catch limits in IOTC purse seine fisheries

In 2016, the IOTC adopted a rebuilding plan in order to address overfishing of the stock of yellowfin tuna (YFT), through the implementation of catch limits for some fisheries and additional measures to reduce the capacity of industrial purse seine fisheries. However, catch controls, while ensuring that overall fishing mortalities are not exceeded, are not implemented properly because some IOTC CPCs exceed targets on a regular basis and not all fisheries are covered by the measures. This is an issue in multi-species fisheries where monitoring of catch in near-real time is complex, especially for industrial tuna purse seine and pole-and-line fisheries, that very often catch juvenile yellowfin tuna and bigeye tuna (BET) when targeting skipjack tuna (SKJ), as those species tend to aggregate forming mixed schools. In other multi-species fisheries, the adoption of measures on one stock may prompt changes of target to other stocks, with a potential to undermine the status of those, -e.g. longline fisheries changing gear configuration, purse seine fisheries shifting from free-school to associated sets, or the contrary, and multi-gear fisheries moving from a gear targeting a stock (pole-and-line targeting skipjack tuna) to another (handline targeting yellowfin tuna).