Ecosystem-­based assessment of a kelp-urchin-­lobster system subject to multiple stressors drives spatial management of Tasmanian lobster fishery towards ecologically sustainable harvest rates

Ecosystem-­‐‑Based Fishery Management (EBFM) has been discussed as a necessity for the viable management of marine resources. However the concept remains difficult to implement despite increasing need for ecosystem-­‐‑based management in the face of multiple anthropogenic and environmental stressors. In eastern Tasmania, the valuable abalone and southern rock lobster fisheries are threatened by formation of sea urchin barrens as a result of overgrazing by the sea urchin (Centrostephanus rodgersii). This circumstance arises from the combined effects of (1) the sea urchin extending its range to eastern Tasmania as a result of ocean warming and shifts in oceanography, and (2) ecological overfishing of its key predator in Tasmania, the southern rock lobster. We developed two independent simulation models that capture the dynamics of the kelp-­‐‑urchin-­‐‑lobster system to assess management strategies. The models show that management to prevent urchin barrens forming is far more achievable than rehabilitating extensive barrens, and they provide clear guidance of targets and alternatives for different levels of risk of loss of kelp beds. Largely as a result of this work, recent changes to management of lobsters have focused on rebuilding biomass. This is one of the few cases of EBFM in practice, informed by modelling complex non-­‐‑linear dynamics.