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Brochier T.,IRD Montpellier | Auger P.,Center Ird Of Lile Of France | Auger P.,University Pierre and Marie Curie | Auger P.,Cheikh Anta Diop University | And 5 more authors.
Ecological Modelling | Year: 2015

At the world scale, many exploited species are currently threatened or undermined by human activities, particularly fishing. Given this situation, establishing artificial habitats (AHs) and marine protected areas (MPAs) is seen as a way of both conserving biodiversity and managing fishing activities. AHs have two main effects: (1) they attract fish from the surrounding areas and concentrate them in the AH, and (2) they increase the capacity of the environment, as a result of the installation of new individuals or, in some cases, of new species. MPAs decrease fish accessibility by constraining the spatial distribution of the fishing effort. We have developed a system of ordinary differential equations (ODEs) that can be used to describe the evolution of fish density, fishing effort, and landings depending on whether AHs are deployed in a MPA or in a fishing area. The analytical study of the ODE system is simplified by means of assuming that processes occur on different time scales. Fish reproduction and landings were assumed to occur at a "slow" time scale, whereas, fish displacement was assumed to occur at a "fast" time scale. For both scenarios of AHs implementation (in an MPA or in a fishing area), we show the existence of different equilibria according to hypotheses based on a purely attractive or purely productive effect of the AH. In all cases, the deployment of AHs in the fishing area leads to an equilibrium with lower fish biomass and lower fish landings than when AHs are deployed within the MPA. This suggests that AHs should not be fished in order to maximize long term fish productivity and fish landings in the surrounding areas. In addition, we attempt to establish a correspondence between our theoretical results and the management plan for artisanal fisheries on the Senegalese coast, which includes the implementation of both AHs and MPAs. This suggests that there is not enough coordination between the non-governmental organizations deploying the AHs and the institutions managing MPAs. Indeed, AHs are usually either immersed in an MPA or subject to local fishing ban, but in fact regulation is inadequate. In this context, the deployment of AHs as part of fisheries management would be premature and could have potentially adverse effects on the resource. © 2014 Elsevier B.V. Source


Auger P.,Center Ird Of Lile Of France | Lett C.,Institute des Systemes Complexes | Moussaoui A.,Abou Bekr Belkaid University Tlemcen | Pioch S.,Caisse des Depots Co
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2010

We present a mathematical model of artificial pelagic multisite fisheries. The model is a stock-effort dynamical model of a fishery subdivided into artificial fishing sites such as fish-aggregating devices (FADs) or artificial habitats (AHs). The objective of the work is to investigate the effects of the number of sites on the global activity of the fishery. We consider a linear chain of fishing sites in which fish are harvested by fishing vessels and a free stock that is unattached to the sites and not exploited. Fish movements between the sites and the free stock, as well as vessel displacements between the sites, are assumed to take place at a faster time scale than the variation of the stock and the change of the fleet size. We take advantage of these two time scales to derive a reduced model governing the dynamics of the total fish stock and the total fishing effort. We show that there exists an optimal number of fishing sites that maximizes the total catch at equilibrium. We finally extend the model to the situation in which both fish attached to the sites and fish in the free stock are exploited. Source


Moussaoui A.,Abou Bekr Belkaid University Tlemcen | Bensenane M.,Abou Bekr Belkaid University Tlemcen | Auger P.,Center Ird Of Lile Of France | Auger P.,University Pierre and Marie Curie | And 2 more authors.
Journal of Biological Systems | Year: 2015

This paper addresses the problem of the optimal size and number of marine reserves to achieve maximum value in commercial fisheries. A simplified network planning situation is analyzed to optimize the size and number of marine reserves. We consider a general 2L-patch model of harvesting population dynamics with continuous time. Fish movements between the sites, as well as vessel displacements between the fishing sites, are assumed to take place at a faster time scale than the variation of the stock and the change of the fleet size. We take advantage of these two time scales to derive a reduced model governing the dynamics of the total fish stock and the total fishing effort. This reduced model is used to determine the optimal size and number of a marine reserves in order to maximize the catch at equilibrium. We show that the optimal number that maximizes the total fish catch at equilibrium depend intricately on the size of the reserve: A small number of reserves is optimal when the size of the reserve is higher and inverse. © 2015 World Scientific Publishing Company. Source


Mansal F.,Cheikh Anta Diop University | Nguyen-Huu T.,Center Ird Of Lile Of France | Nguyen-Huu T.,University Pierre and Marie Curie | Auger P.,Cheikh Anta Diop University | And 3 more authors.
Acta Biotheoretica | Year: 2014

We present a mathematical bioeconomic model of a fishery with a variable price. The model describes the time evolution of the resource, the fishing effort and the price which is assumed to vary with respect to supply and demand. The supply is the instantaneous catch while the demand function is assumed to be a monotone decreasing function of price. We show that a generic market price equation (MPE) can be derived and has to be solved to calculate non trivial equilibria of the model. This MPE can have 1, 2 or 3 equilibria. We perform the analysis of local and global stability of equilibria. The MPE is extended to two cases: an age-structured fish population and a fishery with storage of the resource. © 2014 Springer Science+Business Media Dordrecht. Source

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