Application of the eco-viability approach for the management of mixed fisheries under output control

There is now wide acknowledgement that traditional single-species approaches are not adapted to the management of mixed fisheries as they lack the systemic view required to adequately address the ecological, economic and social dimensions of sustainability. The thesis aims to advance the development of more integrated approaches to advise Total Allowable Catch (TAC) decisions in mixed fisheries by: (1) accounting for technical, but also economic interactions among jointly harvested species, and (2) addressing the variety of sustainability requirements faced in such fisheries. The developed methodology calling on the eco-viability approach has been applied to two mixed fisheries operating in different management contexts: the French demersal fishery in the Bay of Biscay (BoB) and the Australian Southern and Eastern Scalefish and Shark Fishery (SESSF). Explicitly representing the technical and economic interactions structuring mixed fisheries, the ecological-economic simulation model IAM is used to assess the ecological, economic and social impacts of alternative harvest control rules in these fisheries. The thesis notably contributes to improving the representation of human dynamics in the type of models used to advise TAC decisions in mixed fisheries. It particularly discusses the implications in terms of provided advice of accounting for dynamics in the allocation of fishing effort, the trading of individual quotas and fish markets. The thesis also focuses on how the multiple dimensions of sustainability can be considered in the provision of fisheries management advice. The eco-viability approach is used here to identify future paths maintaining a fishery within ecologically, economically and socially acceptable bounds. Specifically, biological sustainability pertains to maintaining harvested stocks above a limit biomass threshold. Economic sustainability refers to the ability of fleets or vessels to ensure the remuneration of both physical and human forms of capital. Finally, an upper limit on the price of fish is considered to ensure that fish remains affordable to the consumer. Regarding modelling developments, the thesis presents a process-based model of ITQ (Individual Tradable Quotas) markets in mixed fisheries that captures the economic incentives that ITQ markets provide in a multi-species context, notably those to redirect fishing effort towards species not under quota or the TAC of which is not constraining. Numerical simulations in the SESSF also show the flexibility that exists in the fishery to adjust fishing practices to quota availability, thereby highlighting the importance of accounting for fishing dynamics when advising TAC decisions in mixed fisheries. Finally, eco-viability analyses carried out in both fisheries highlight trade-offs between conservation and economic objectives but also trade-offs pertaining to the distribution of benefits between capital owners, crews, and consumers.