Review and update harvest strategy settings for the Commonwealth small pelagic fishery
CSIRO Oceans and Atmosphere Hobart
Tony D. Smith
The SPF has been the focus of considerable stakeholder scrutiny in 2012. Part of this focus has been on the harvest strategy, which has been in place since 2009. Two questions have arisen about the current harvest strategy: 1) What reference points for exploitation rates are appropriate for the species exploited in this fishery, taking into account their ecological role in the food chain? 2) Is the maximum exploitation rate specified in the strategy appropriate for all the target species, given their different productivities, life histories and trophic importance? Questions have also been raised about the possibility and impacts of localised depletion in this fishery, but these will not be dealt with in this proposal. There is an urgent need to review and if necessary update the harvest strategy settings for the SPF. Specifically, there is a need to answer the two questions outlined above, both of which involve settings in the current harvest strategy. One concerns appropriate choice of target (and limit) reference points, while the other concerns selecting individual harvest rates for each of the target species in the fishery, appropriate to its life history and productivity. Notwithstanding that the vessel which caused the high level of scrutiny on the fishery has departed Australian waters, answering the two questions remains fundamental to proper implementation of the Commonwealth Harvest Strategy Policy for this fishery. The need for a review of the harvest strategy settings had been flagged by SPF RAG ahead of the contorversy with the "super trawler".
1. Provide advice on best practice reference points for the four main target species in the SPF
2. Provide advice on suitable exploitation rates to achieve management targets for the four main target species in the SPF
The study used a new variant of the Atlantis ecosystem model (Atlantis-SPF). The model found that both singly and in combination, depleting these target species has only minor impacts on other parts of the ecosystem. Unlike some other regions which show higher levels of dependence on similar species, such as in Peru and the Benguela systems (Smith et al., 2011), the food web in southern and eastern Australia does not appear to be highly dependent on SPF target species. None of the key higher trophic level predators in SE Australia, such as seals, penguins and tunas, have a high dietary dependence on these species. Studies using other ecosystem models such as Ecosim in the same region have reached similar conclusions (Goldsworthy et al., 2013; Bulman et al., 2011).
The findings have implications for the target and limit reference points that should be selected for the main commercial species in the SPF. Equilibrium BMSY for these species ranged from about 30 to 35% of unfished levels. However, these levels are uncertain and it may be more appropriate to use the default values from the HSP with BMSY set at B40 (40% of unfished levels) and the default BMEY set at 1.2 times this level, close to B50. This study suggests that the target reference point for these SPF target species should be set at B50 and the limit reference point at B20, in line with the HSP default settings. The results presented in this report, combined with evidence from other studies, suggest that these levels are safe from an ecosystem perspective and provide reasonable levels of yield relative to MSY.