Informing ecosystem-based management of the range extending long-spined sea urchin using a structured decision making process

The poleward movement of species is a global signature of climate change, which can affect regional biodiversity, ecosystem structure and functioning and pose significant challenges for managers of marine resources. This is particularly the case where there are multiple stakeholders with different and often conflicting views on appropriate management action. A structured consultative decision making process can assist managers in identifying some disparity between objective and subjective elements that may underpin stakeholder disagreement.

Following rapid climate-driven changes in ocean currents, the long-spined sea urchin (Centrostephanus rodgersii) has extended its range from Australia’s mainland to eastern Tasmania. Due to the depletion of large rock lobster (Jasus edwardsii), its main predator on Tasmanian reef, by fishing, C. rodgersii has demonstrated the ability to form and maintain extensive ‘barrens’, i.e. bare rocks following the destructive grazing of macroalgal cover. Relative to dense seaweed beds, sea urchin ‘barrens’ represent a dramatic loss of habitat, biodiversity and productivity for important commercial reef species such a southern rock lobster (Jasus edwardsii) and abalone (Haliotis rubra). A small-scale commercial harvesting operation for C. rodgersii has developed over the last five years. Thus, the range of ecological, social and economic consequences associated with the range extension of C. rogersii to eastern Tasmania generates conflicts between different stakeholder groups (commercial and recreational fishers, as well as conservation sectors) and poses complex challenges for the regional management of reef communities and fisheries.

In this paper, we applied a Structured Decision-Making framework to help managers and stakeholders with identifying cost-effective interventions that perform well against conflicting management objectives. We conducted a workshop and two successive surveys involving 12 representatives from key stakeholder groups to elicit and rank a suite of performance objectives and management scenarios. We then estimated the consequences of alternative management scenarios using the TRITON model, which realistically captures the dynamics of Tasmanian reef communities. 10-year consequences of management interventions on reef state (i.e. algal cover and reef species biomass densities) and fisheries productivity were simulated with the model. Additionally, we assessed the cost and feasibility of available management interventions. We directly and indirectly elicited stakeholders’ preferences for different scenarios using the simulated consequences of alternative management strategies. Quantification of scenarios performances against stakeholders’ preferences, as well as benefits, cost and feasibility of management interventions were then used independently and in linear combination to estimate alternative quantitative cost-effectiveness ranking metrics. The range of quantitative performance metrics allowed to rank scenarios overall performance, as well as how they benefit individual stakeholder groups. This model-informed structured decision making process contributed to overcome some of the initial conflicts and led to a larger agreement between the different interest groups about best management scenarios. Enforcement of a zonal cap on both recreational and commercial catches of rock lobster combined with either, sea urchin harvesting, or lobster biomass translocation ranked as most cost-effective management scenarios.