Abdoul Cisse

A bio-economic model for the ecosystem-based management of the coastal fishery in French Guiana

This paper offers a theoretical and empirical modeling for ecosystem-based fishery management (EBFM). A multi-species and multi-fleets model integrating Lokta-Volterra trophic dynamics and profit functions is developed for the coastal fishery of French Guiana. This small-case fishery constitutes a challenging example with high fish biodiversity, several non selective fleets and a potentially increasing local food demand due to demographic pressure. The dynamic model is calibrated with thirteen species and four fleets using catch and effort data on a monthly basis from 2006 to 2009. Several contrasting fishing scenarios including status quo, total closure, economic and viable strategies are simulated and compared from both biodiversity preservation and socio-economic performance viewpoints. We show that fishing outputs including food supply and profitability of fleets can be sustained although a significant loss of biodiversity cannot be avoided.

Ecological-economic modelling for the sustainable management of biodiversity

Terrestrial and marine biodiversity provides the basis for both ecosystems functioning and numerous commodities or services that underpin human well-being. From several decades, alarming trends have been reported worldwide for both biodiversity and ecosystem services. Therefore the sustainable management of biodiversity requires a double viewpoint balancing ecological conservation with the welfare of human societies. Understanding the underlying trade-offs, synergies and interactions imposes the development of interdisciplinary researches and methods. In that respect, bio-economic or ecological economic modeling is likely to play a major role. The present paper intends to elicit the key features, strengths and challenges of bio-economic approaches especially in mathematical and computational terms. It first recall the main bio-economic methods, models and decisional instruments used in these types of analyses. Then the paper shows to what extent bio-economic sustainability lies between equilibrium, viability and optimality mathematical frameworks. It ends up by identifying new major challenges among which the operationalization of ecosystem based management, the precautionary principle and the implementation of governance are especially important.

The Tragedy of Open Ecosystems

This paper investigates the role played by cooperation for the sustainable harvesting of an ecosystem. To achieve this, a bio-economic model based on a multi-species dynamics with interspecific relationships and multi-agent catches is considered. A comparison between the non-cooperative and cooperative optimal strategies is carried out. Revisiting the Tragedy of Open Access and over-exploitation issues, it is first proved analytically how harvesting pressure is larger in the non-cooperative case for every species. Then it is examined to what extent gains from cooperation can also be derived for the state of the ecosystem. It turns out that cooperation clearly promotes the conservation of every species when the number of agents is high. When the number of agents remains limited, results are more complicated, especially if a species-by-species viewpoint is adopted. However, we identify two metrics involving the state of every species and accounting for their ecological interactions which exhibit gains from cooperation at the ecosystem scale in the general case. Numerical examples illustrate the mathematical findings.