Developing risk equivalent data-rich and data-limited harvest strategies

Several fisheries jurisdictions are aiming to achieve risk equivalency (here defined as the probability of a stock being depleted below a limit reference point or not being maintained at a target reference point) irrespective of the stock assessment method used to provide management advice and the amount of data available. Risk equivalency is implicitly required under the USA Magnuson-Stevens Act, while in Australia it is an explicit component of the Australian Commonwealth Government’s Harvest Strategy Policy. Risk equivalency is well understood, but few fisheries have attempted to implement it. The Australian Southern and Eastern Scalefish and Shark Fishery (SESSF) is the only Australian fishery that has explicitly done so, albeit in a semi-arbitrary manner. Assessments and associated harvest strategies are placed into tiers from data-rich to data-limited. There are also meta-rules that control how much catch limits can change from one year to the next, and buffers by tier to achieve risk equivalency. Here, the SESSF tier system was evaluated in an ecosystem context using Management Strategy Evaluation. Two buffer systems were considered, the current SESSF system and a system inferred from how the Acceptable Biological Catches are set for the USA west coast groundfish fishery. Harvest strategies for all tiers were capable of moving productive stocks so their biomasses lay between the limit and target reference points. The USA buffer system was more conservative than the SESSF system, and achieved the fastest recovery for depleted stocks. The latter system led to slightly lower total catches, but was closest to achieving risk equivalency across the tiers. The USA buffer system led to biomass trajectories most similar to those when the system was managed so that biomass moves as rapidly as possible to its target reference point.