Implementation of dynamic reference points and harvest strategies to account for environmentally-driven changes in productivity in Australian fisheries
Pisces Australis Pty Ltd
Recently, the risks resulting from not accounting for variability in productivity have become translated into potential risks associated with environmentally driven trends in recruitment, particularly the risk created by ongoing declines in recruitment (and/or growth) driven by climate-change induced trends in water temperature, weather and current patterns. A number of southeast Australia fish stocks have failed to 'recover' following substantial reductions in catch and effort, and a number of research projects have concluded that some of these have undergone an environmentally-driven reduction in productivity. A productivity shift has already been demonstrated for Eastern Jackass Morwong, with the stock-recruit relationship and reference points being adjusted to reflect this change. Ecosystem and climate-change modelling have predicted increasing likelihood of similar changes in productivity for a number of Australian fish stocks. Current harvest strategies assume either equilibrium or some average B0, and associated target (B48) and limit (B20) reference points. Use of equilibrium B0-based reference points and harvest strategies do not correctly reflect the natural dynamics of stocks where productivity changes. This can lead to sub-optimal management, either over-utilising a reduced productivity stock or under-utilising an increased productivity stock. In contrast, reference points based on some proportion of naturally variable unfished biomass (Bunfished or dynamic B0) will fluctuate to follow environmentally-driven productivity changes. Dynamic reference points have been evaluated and adopted for a number of international fisheries. The need to adapt stock assessment methods and harvest strategies to explicitly and justifiably account for shifts in productivity has been recognised by the AFMA Resource Assessment Group for the Southern and Eastern Scalefish and Shark Fishery (SESSF), not least as a result of clearly evident declines in biomass (Jackass Morwong, Redfish) or recruitment (Silver Warehou) that cannot be attributed to fishing under current productivity assumptions.
1. To review relevant international research and management approaches to account for environmentally-driven productivity change in stock assessments, reference points and harvest strategies for selected Australian fish stocks.
2. To identify and describe circumstances and fish stocks for which dynamic reference points should or should not be used in stock assessments and harvest strategies, and develop appropriate methodology for conducting assessments using dynamic reference points.
3. To identify selected candidate fish stocks showing likely environmentally-driven productivity change, conduct comparative assessments for these stocks using equilibrium and dynamic reference points, and prepare a candidate harvest strategy that includes dynamic reference points for testing in the FRDC Multi-Species Harvest Strategy project.
4. To make recommendations on future implementation of dynamic reference points and harvest strategies for Australian fish stocks.
5. To develop and improve methods for detecting and quantifying changes in productivity (growth and recruitment) in stock assessments, to relate these to environmental mechanisms causing productivity changes, and to evaluate data needs, including environmental indices, required to usefully detect and evaluate productivity change under various circumstances.
6. To consider and evaluate options for effective harvest control rules, incorporating dynamic reference points, that might appropriately respond to changes in fish stock productivity, including environmentally driven trends in productivity.
7. To identify environmental circumstances and fish stock characteristics under which it would be appropriate and advisable to move to using assessments and management approaches incorporating dynamic productivity and reference points, vs. stocks for which dynamic approaches offer no benefit compared to existing equilibrium approaches.
8. To make recommendations on future stock assessment approaches, data requirements, harvest control rules and management approaches incorporating environmental indicators, dynamic productivity and dynamic reference points for Australian fish stocks.