Simple fishery and marine reserve models to study the sloss problem

Abstract

Abstract. Habitat fragmentation is generally believed to be detrimental to the persistence of natural populations. In nature management one therefore tends to prefer many small nature reserves over one single large having equal total area. The paper presents two tractable analytical models to examine whether this preference is warranted in a metapopulation framework with reserves (patches) by formulating the dependence of the density as well as the global catch on the number of reserves. Studying these models, we seek to compare the two different strategies: whether a single large reserve will (1) conserve more species and (2) maintains high yield in fisheries than several small or vice versa? Our results indicate that it is favourable to make several small reserves instead one single large reserve. Indeed, at equilibrium, the density as well as the global catch are bigger in the Several Small (SS) strategy than in the Single Large (SL) one. In addition, in the case of SS strategy, an intermediate reserve number exists which is optimal for catch at equilibrium. The results in this paper may provide important implications for nature conservation.Résumé. La fragmentation de l'habitat est généralement considéré comme préjudiciableà la persistance des populations naturelles. Dans la gestion des milieux naturels, il y a donc tendanceà préférer plusieurs petites réservesà une seule ayant la même superficie. Ce papier présente deux modèles mathématiquesétudiant ce problème dans le cadre d'une métapopulation avec des zones protégées représentés par des sites discrets. Nousétudions notamment les captures globales en fonction du nombre de réserves. Nous cherchons par cetteétudeà comparer deux stratégies de préservation : Une seule grande réserve ou plusieurs petites. Nos résultats indiquent qu'il est préférable de mettre plusieurs petites réserves plutôt qu'une seule réserve. En effet,à l'équilibre, la densité ainsi que la capture globale sont plus grandes dans le cas de la stratégie avec plusieurs petites réserves (SS) que dans le cas d'une seule grande (SL). En outre, dans le cas de la stratégie SS, nous démontrons qu'il existe un nombre optimal de reserves qui maximise la capture totaleà l'équilibre. Les résultats présentés dans cette contribution sont susceptibles d'avoir des implications importantes dans le domaine de la conservation des espèces.

Groups of small lakes maintain larger microalgal diversity than large ones

“…The SLOSS debate inevitably attracted many theoretical approaches and explanations, and the roots of this dilemma are deeply embedded in conservation management and landscape planning. Although a popular view is, that protection of larger sized areas is better (Tscharntke et al, 2002) investigations of different sized habitats and different animal and plant groups revealed that there are arguments on "both sides of the SLOSS-debate" (Tscharntke et al, 2002;Moussaoui and Auger, 2015). There is no doubt, fragmented landscape is a common phenomenon worldwide, and creation of large, contiguous protected areas is only rarely feasible (Gaz and Garcia-Boyero, 1996).…”

Limited Contribution of Small Marine Protected Areas to Regional Biodiversity: The Example of a Small Canadian No-Take MPA

“…Not all MPAs are effective at meeting their goals and meaningful measurement of what constitutes adequate conservation of a species, habitat, or ecosystem remains a challenge. While there is no universal formula for ensuring MPA success (Moussaoui and Auger, 2015), size of the protected area is an important factor (Claudet et al, 2008;Edgar et al, 2014). In a global study of 87 MPAs, Edgar et al (2014) identified five characteristics, called "NEOLI, " that are shared by successful MPAs: No take, well Enforced, Old (>10 years), Large (>100 km 2 ), and Isolated.…”

Model of two competing populations in two habitats with migration: Application to optimal marine protected area size

“…Finally, the relationship between migration and maximum sustainable yield (MSY) can be examined in the context of conditions for optimal size of wildlife reserve, especially marine protected areas (MPA). In previous works on the optimal MPA size (Hastings and Botsford 1999, Moussaoui and Auger 2015, Takashina 2020, singlespecies populations having a very high or moderate migration rate were considered. In this manuscript, we examined populations of two competing species at relatively low migration rates.…”