Mardi 20 janvier 2015
Salle B110 – Bât.B – UBO
« Vers une gestion écosystémique des effets de la pêche et du climat sur les récifs tempérés du sud-est de l’Australie »
Par Martin Marzloff, Institute for Marine and Antarctic Studies, University of Tasmania
My talk will be structured into three sections, as follows:
(1) Predicting and managing the ecological impacts of marine species on the move using qualitative network models Worldwide, a large proportion of species are undergoing sustained climate-driven changes in their distributions. The ecological, social and economic consequences of these range-shifts on regional ecosystems can be large and hard to reverse, but remain challenging to predict and pro-actively manage. Based on qualitative knowledge about regional ecosystem structure and range-shifting species, our generic framework can help identify in dividual range-shifting species, or groups of species, that can have widespread detrimental effects on ecosystem structure and productivity. Using temperate reef systems in southeastern Australia as a case study, our finding s suggest that the negative impacts of simultaneous range-shifts are synergistic, and hence, can only be effectively mitigated by ecosystem-based management strategies that combine multiple management interventions.
(2) Simulation modelling & ecosystem-based management of the Tasmanian rock lobster fishery 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 by fishing of large rock lobster (Jasus edwardsii), its main predator on Tasmanian reef, 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). TheTRITON model, specifically developped to realistically captures seaweed bed-seaurchin-rock lobster community dynamics, provide ecosystem-based guidance for the regional management of rocky reef communities.In particular, simulations help define effective interventions and a safe operating space, which recognises the central role of rock lobster to reef dynamics, so as to prevent phase shifts in reef dynamics from (i) dense, species-rich, productive seaweed beds to (ii) impoverished and widespread sea urchin ‘barrens’.
(3) Structured Decision-Making process involving stakeholders towards ecosystem-based management of Tasmania reefs and fisheries. Finally, I will present some results from a Structured Decision-Making framework recently developped around the TRITON model to help managers and stakeholders with identifying cost-effective in terventions that perform well against conflicting management objectives. A workshop and two succesive surveys involving 12 representatives from key stakeholder groups were run to elicit and rank a suite of performance objectives and management scenarios. Bycombining stakeholders’ preferences, as well as cost and feasibility of available management interventions, we derived alternative cost-effectiveness ranking metrics. Enforcement of a zonal cap on both recreational and commercial catches of rock lobster combined with either, sea urchin harvesting, or lobster biomass translocation overall rank amongst the most cost-effective management scenarios.