Can Fishing Pressure Invert the Outcome of Interspecific Competition? The Case of the Thiof and of the Octopus Along the
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Can Fishing Pressure Invert the Outcome of Interspecific Competition? The Case of the Thiof and of the Octopus Along the Senegalese Coast Thuy Nguyen-Phuong1 • Doanh Nguyen-Ngoc2,3 Pierre Auger4,5 • Sidy Ly6 • Didier Jouffre7
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Received: 14 December 2015 / Accepted: 7 October 2016 Springer Science+Business Media Dordrecht 2016
Abstract We present a mathematical model of two competing marine species that are harvested. We consider three models according to different levels of complexity, without and with species refuge and density-independent and density-dependent species movement between fishing area and refuge. We particularly study the effects of the fishing pressure on the outcome of the competition. We focus on conditions that allow an inferior competitor to invade as a result of fishing pressure. The model is & Doanh Nguyen-Ngoc [email protected] Thuy Nguyen-Phuong [email protected] Pierre Auger [email protected] Sidy Ly [email protected] Didier Jouffre [email protected] 1
School of Applied Mathematics and Informatics, Hanoi University of Science and Technology, No. 1 Dai Co Viet Street, Hai Ba Trung District, Hanoi, Vietnam
2
Faculty of Computer Science and Engineering, Thuyloi University, No. 175, Tay Son Street, Dong Da District, Hanoi, Vietnam
3
UMI 209 UMMISCO, IRD/UPMC Paris 6, 32 Avenue Henri Varagnat, 93143 Bondy Cedex, France
4
Univ Paris 06, Sorbonne Universite´s, IRD, UMI 209, UMMISCO, Bondy, France
5
Universite´ Cheick Anta Diop, UMI 209 IRD UMMISCO-UCAD, Dakar, Senegal
6
University Cheikh Anta Diop, FASEG-LMDAN, Dakar, Senegal
7
Institut de Recherche pour le De´veloppement (IRD), UMR 248 MARBEC, LABEP-AO (IRDIFAN), BP 1386, Dakar, Senegal
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T. Nguyen-Phuong et al.
discussed in relationship to the case of the thiof and the octopus along the Atlantic West African coast. At the origin, the thiof was abundant and the octopus scarce in that region. Since, the fishing pressure has strongly increased in some fishing areas leading to the depletion of the thiof and the invasion of its competitor, the octopus. Keywords Competition Refuge Density-dependent migration Densityindependent migration Fishing pressure
1 Introduction The North western African coast lying from the Saharan bank to the Guinean shelf is known to be one of the most productive marine area in world due to hydroclimatic conditions that induce the presence of a strong regional up-welling system (Arı´stegui et al. 2009; Demarcq 2009; Roy 1991). In link with this high level of biological productivity, this marine area is subjected to a very ancient fishery exploitation (Bravo de Laguna and Balguerias 1993), with a fishing pressure that began to reach very high rate during the last past half century (Amaratunga 1987; Balguerı´as et al. 2000; Chavance et al. 2004; Rathjen and Voss 1987) and is still increasing from the sixties until now (Chavance et al. 2004). This evolution of the fishing pressure led ecological changes and important evolutions within the marine communities, in particular within the
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