SPF Harvest Strategy: Management Strategy Evaluation Update

1. SPF Harvest Strategy:Management Strategy Evaluation Update SPF Scientific Panel January 2017

2. What is a Harvest Strategy? Also known as a ‘Management Procedure’ or ‘Operational Management Procedure’, a Harvest Strategy (under the Commonwealth Harvest Strategy Policy) is: • A set of agreed rules intended to specify the management action to be taken in response to agreed indicators of stock status. Harvest Strategies are quantitatively tested to ensure that they will achieve the stated objectives, with the required probability, under specified conditions. Harvest Strategies typically consist of: • Clearly stated and measurable objectives, including the required probability of achieving those objectives; • Agreed indicators to be used to indicate current status or change in status, including the data to be collected to ensure that the indicators will be available; • An agreed decision rule or rules, specifying how management measures, such as the TAC, should change in response to the indicators used. • A meta-rule or meta-rules specifying what alternative action must be taken if the indicators of stock status move outside the bounds tested during management strategy evaluation.

3. Management Strategy Evaluation Management Strategy Evaluation (MSE) is the process of testing and tuning proposed decision rules for a harvest strategy to ensure that they will achieve the required objectives with the required probability: • Designed to model the species population dynamics; tuned to historical fishery and biological data; • Updated annually with Recruitment, Growth, Natural Mortality and Catch. Operating Model (Stock assessment model) {Change in TAC} • Bcurrent, B/B0 • Prob B < 0.2B0 • Catch / MSY; • Variance on the above. Management Response Stock Status Output Iterated annually to give projections for required period of years Harvest Strategy Decision Rule • Tuned to achieve objectives: Sardine: • < 5 years: E=0.2 • 6-10 years: E=0.1 • >10 years: E=0.05 • Atlantis; E=0.025 Evaluation of Indicators • Last DEPM biomass estimate; • Years since last DEPM.

4. Additional MSE analysis were conducted using updated operating models based on initial catch-at-age stock assessment models for eastern Jack Mackerel and Blue Mackerel.

5. Targets and Limits • The supporting stock assessment work (Punt et al. 2016) indicates that jack mackerel and blue mackerel show little relationship between CPUE and biomass over the ranges of biomass and catches observed historically. • Under these conditions, economic analysis concludes that biomass at MEY does not lie above biomass at MSY, so the biological target MSY becomes the important target to achieve.. • Previous ecosystem analyses concluded that these pelagic species form moderate components of predator diets, and that biomass levels maintained at or near MSY (30% - 36% B0 for these species) are adequate to maintain ecosystem functioning. • Nonetheless, to provide an additional biomass buffer, a Target Reference Point of 50% has been proposed, above the HSP default proxy MEY level. • There is no scientific justification for revising the Target Reference Point of 50% B0 or the Limit Reference Point of 20% B0.

6. Management Strategy Evaluation Update • Previous MSE analysis (Smith 2015) provided harvest rates that ensured < 1 in 10 year risk of breaching the limit at Tiers 1 and 2. • The MSE update confirmed that the proposed Tier 3 maintains risk equivalency across Tiers, with little change in recommended initial Tier 1 harvest rates if Tier 3 is incorporated at 50% of Tier 2.

7. Management Strategy Evaluation Update • The additional MSE work also explored wider ranges in productivity, particularly alternative stock-recruit relationships and recruitment variability. Expectedly, low productivity scenarios result in lower recommended exploitation rates. • However, these assessments assume that fluctuations in catches reflect fluctuations in recruitment when, in reality, catches in the SPF have often been driven by other factors such as economics. • Recruitment estimates generated by the assessments are unlikely to reflect the true population dynamics and may over-estimate recruitment variability.

8. Static vs. Dynamic B0 • These analyses also used a static (equilibrium) estimate of B0, which is not appropriate for stocks that show highly variable recruitment, as many small pelagic species do. • For such species, assuming a fixed target and limit results in over-estimation of depletion and risk. For species with highly variable productivity, a dynamic B0 (BUnfished) needs to be used. • Further work is required to evaluate dynamic targets and limits, and to better understand the true recruitment dynamics of these species.

9. SPRFMO Jack Mackerel Assessment South Pacific Chilean jack mackerel shows highly variable, probably environmentally driven, recruitment. As a result, even in the absence of fishing, the stock biomass would have declined by over 50% between 1989 and 2010. Dynamic targets and limits need to be used for such species,

10. SPRFMO Jack Mackerel Assessment Trends in South Pacific jack mackerel recruitment appear to be driven partially by environmental factors, showing some relationship with the Inter-decadal Pacific Oscillation Index. Exceptionally high recruitment in 1985 and 1986 resulted in a tripling of biomass by 1989.

11. Questions?