Development and evaluation of management procedures in pāua quota management areas 5A, 5B and 5D

This project was a first attempt at introducing formal management procedures (MPs) based on control rules in pāua fisheries in New Zealand. Stakeholders in pāua quota management area PAU 5 requested that science-based management procedures be investigated in order to ensure long-term sustainability of pāua fisheries in lower South Island and Stewart Island. The MPs were to be used for voluntary management within the industry in the medium term (e.g., for the next 3–5 years) to trial the process. Once the process and the MPs were refined and meeting stakeholders’ expectations, they could be used for setting the total allowable commercial catch (TACC).

The development process for the MPs included three phases: initially, the current pāua stock assessment model was used to produce up-to-date status estimates for all stocks, and an added MP evaluation loop was used to test preliminary rules. The outcome of this pilot run was the basis for the development of a web application that was used to consult with fishers and inspect the outcomes of individual model runs.

A series of meetings was held with fishers and quota-owners in PAU 5 to quantify objectives and identify control rules that are acceptable to stakeholders. Management objectives were stated qualitatively as low risk/high biomass objectives, and rules were discussed that fishers considered as leading to desirable outcomes (i.e., high biomass and low risk in the context of the management objectives).

Agreed rules were simulation-tested based on the period 2016–2036 using the pāua stock assessment model. This testing involved a number of scenarios, including scenarios that were explicitly requested by PAU 5 stakeholders (e.g., scenarios relating to increased recreational catch). The MP evaluations showed that rules suggested by fishers are likely robust, and near optimal with respect to identified objectives for PAU~5A and PAU~5B. For both these fisheries, the proposed rules led to likely outcomes of biomass levels above 40% of virgin spawning stock biomass SSB₀.

In PAU 5B, the proposed rule could be used to motivate an increase in TACC, as all scenarios suggest continued rebuilding of biomass towards a level near 60% of spawning stock biomass and catch-per-unit-effort (CPUE) around 50 kg/h. In PAU 5A, the proposed control rules would likely lead to steady increases in biomass to levels well above 40% of SSB₀. Nevertheless, the rules also suggested that the current shelving needs to be maintained under conservative management objectives.

The proposed control rule for PAU 5D likely leads to steady rebuilding, but there is only a small chance that biomass levels will be above 40% of SSB₀ in the medium term, despite current shelving of 30% of the TACC. Under the proposed control rule, shelving levels would likely be reduced relatively quickly, and an agreement to maintain current shelving levels would help faster rebuilding. The evaluation of the MPs thus suggested a difficult trade-off in PAU 5D between continued catch and rapid rebuilding to target levels.

The proposed control rules appear to be a robust starting point for managing PAU 5 fisheries on the basis of formal, but voluntary, management procedures. Most sensitivities, including those with increased recreational catch, had limited impact for the sustainability of the PAU 5 fisheries under the proposed rules. Increased recreational catch did lead to lower commercial catch in these scenarios, but over-all, reduced productivity (through low future recruitment) had the strongest impact on performance of control rules and often led to declines in biomass under rules considered here. However, only in PAU 5D did simulated declines under reduced productivity lead to high probability of triggering limit reference points.