The effects of marine protected areas over time and species dispersal potential: A quantitative conservation conflict attempt

📝 Abstract

Protected areas are an important conservation measure. However, there are controversial findings regarding whether closed areas are beneficial for species and habitat conservation as well as landings. Species dispersal is acknowledged as a key factor for the design and impacts of closed areas. A series of agent based models using random diffusion to model fish dispersal were run before and after habitat protection. All results were normalised without the protected habitat in each scenario to detect the relative difference after closing an area, all else being equal. Results show that landings of species with short dispersal ranges will take longer to reach the levels of pre Marine Protected Areas (MPAs) establishment than landings of species with long dispersal ranges. Further the establishment of an MPA generates a higher relative population source within the MPA for species with low dispersal abilities than for species with high dispersal abilities. Results derived here show that there exists a win-win feasible scenario that maximises both fish biomass as well as fish catches.

💡 Analysis

Protected areas are an important conservation measure. However, there are controversial findings regarding whether closed areas are beneficial for species and habitat conservation as well as landings. Species dispersal is acknowledged as a key factor for the design and impacts of closed areas. A series of agent based models using random diffusion to model fish dispersal were run before and after habitat protection. All results were normalised without the protected habitat in each scenario to detect the relative difference after closing an area, all else being equal. Results show that landings of species with short dispersal ranges will take longer to reach the levels of pre Marine Protected Areas (MPAs) establishment than landings of species with long dispersal ranges. Further the establishment of an MPA generates a higher relative population source within the MPA for species with low dispersal abilities than for species with high dispersal abilities. Results derived here show that there exists a win-win feasible scenario that maximises both fish biomass as well as fish catches.

📄 Content

Article in press – accepted ms version to appear in the Journal Web Ecology in 2016

The effects of marine protected areas over time and species’ dispersal potential: A quantitative conservation conflict attempt

Aristides Moustakas1,*

1. School of Biological and Chemical Sciences Queen Mary, University of London Mile End Road, London E1 4NS, UK

• Corresponding author Aris Moustakas Email: arismoustakas@gmail.com

Abstract Protected areas are an important conservation measure. However, there are controversial findings regarding whether closed areas are beneficial for species and habitat conservation as well as for harvesting. Species dispersal is acknowledged as a key factor for the design and impacts of protected areas. A series of agent based models using random diffusion to model fish dispersal were run before and after habitat protection. All results were normalised without the protected habitat in each scenario to detect the relative difference after protecting an area, all else being equal. Model outputs were compared with published data regarding the impacts over time of MPAs on fish biomass. In addition data on species’ dispersal potential in terms of km per year are compared with model outputs. Results show that fish landings of species with short dispersal rates will take longer to reach the levels before the Marine Protected Areas (MPAs) were established than landings of species with long dispersal rates. Further the establishment of an MPA generates a higher relative population source within the MPA for species with low dispersal abilities than for species with high dispersal abilities. Results derived here show that there exists a win-win feasible scenario that maximises both fish biomass as well as fish catches.

Keywords Agent based models; conservation conflicts; win-win scenarios; fisheries management; reserve management; human – wildlife interactions; dispersal; scale; model validation.

1. Introduction Habitat protection is a complex issue which has only recently achieved high public visibility [1]. In marine environments it covers many aspects, such as conservation of juvenile fish habitats, protection of corals, and development of marine recreational parks or dive sites. Fishing is often seen as a destructive force, and habitat destruction by fishing practices has to be considered in any comprehensive management plan [2]. Habitat protection can be total or partial. Total closures are often associated with Marine Protected Areas (MPAs) and the designation of certain areas for alternate uses such as recreation. Closing an area affects several stakeholders: Closed areas are of interest to biologists, conservation scientists, land use planners, but also fishermen and the fishing industry in general as well as the tourism industry [3,4]. While there are cases where closed areas are beneficial for species and habitat conservation [2,5] there are also studies that question the benefits of closures from the economic perspective regarding fish landings [2,6]. This in turn has implications for both food security [7] as well as economic impacts on fisheries [8-10]. Thus a win-win scenario in terms of both increased fish biomass as well as increased fish landings after establishing an MPA is ideal [11] but questionable.
   The design of MPAs involves specifying the total surface area to be protected, the distribution in space of that area, and its connectivity [12]. That leaves a fairly wide range of choices: there is controversy about whether single large reserves are more effective than several smaller ones of the same total area (SLOSS), whether edge effects diminish their efficacy, and whether closely spaced reserves are more effective than distantly spaced ones [12]. It is acknowledged that dispersal is a key factor in designing MPAs [13,14]. The reasons behind dispersal been a key factor [15] are that: (i) MPAs should be large enough so that adults can stay long enough inside them, but how large is large enough is clearly related with dispersal potential, (ii) MPAs should be close enough so that larvae can move between them, but how close is close enough is also related to dispersal potential. Assuming dispersal to be an important factor in determining the ability of species to reach the protected areas then the impacts on species with different dispersal abilities may vary in time since the establishment of an MPA [16,17] for various reasons related with species growth rates or the ability of species to reach or remain within the MPA.. Here, assuming all other factors that influence the efficacy of MPAs to remain equal, it is investigated what are the impacts of MPA(s) on biomass inside and outside the reserves as well as on landings over time to species with different dispersal abilities. In an effort to provide the relative differences in fish biomass and fish landings with and without MPAs, agent based simulat

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