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Using reef fish movement to inform marine reserve design

2016; Wiley; Volume: 54; Issue: 1 Linguagem: Inglês

10.1111/1365-2664.12736

1365-2664

Rebecca Weeks, Alison L. Green, Eugene Joseph, Nate Peterson, Elizabeth Terk,

Ichthyology and Marine Biology

A central tenet of protected area design is that conservation areas must be adequate to ensure the persistence of the features that they aim to conserve. These features might include species, populations, communities and/or environmental processes. Protected area adequacy entails both good design (e.g. size, configuration, replication) and management effectiveness (e.g. level of protection, compliance with regulations). With respect to design, guidelines recommend that protected area size be informed by species' home ranges, as individuals that move beyond protected area boundaries are exposed to threats and are thus only partially protected (Kramer & Chapman 1999). This is especially important for species that are directly exploited, as are many coral reef-associated fishes. Information on movement patterns of coral reef fishes has only recently been summarized in the literature, along with guidelines on how this information might be used to inform the adequate design of marine protected areas (MPAs; Green et al. 2015). Here, we demonstrate, using an example from Micronesia, how these guidelines can be adapted and applied within a particular socio-ecological context to guide discussions with stakeholders aimed at improving the efficacy of an existing protected area network. We discuss aspects of this process that were successful and those that were challenging, and in so doing, identify areas where future ecological research effort might benefit protected area planning and design. To achieve objectives for biodiversity conservation and/or fisheries management, MPAs must be able to sustain focal species within their boundaries throughout their juvenile and adult life-history phases, when they are most vulnerable to fishing. Thus, MPA size should be informed by focal species' home ranges (Kramer & Chapman 1999). This information can be obtained through a variety of empirical methods, including acoustic telemetry, tag–mark–recapture, satellite tracking or underwater observations (Green et al. 2015). However, poor availability of information on home range movements of key species has meant that practitioners have relied upon generic rules of thumb for MPA size (Moffitt, White & Botsford 2011). Despite evidence that small (e.g. 2 times species home range), marginal (shortest distance within the bounds of species home range estimates) or poor (shortest distance less than species home range) (Fig. 1). Data on the spatial distribution of fishing pressure were unavailable, but would have allowed us to consider estimates of partial protection afforded to individuals whose home ranges span MPA boundaries, refining these classes. Rather than presenting this information in the first instance, we provided workshop participants with information on focal species' home ranges and the size of each MPA to perform the analyses themselves in breakout groups. A visual depiction of the effective size of each MPA relative to the home range movements of focal species was later included on MPA-specific evaluation cards (Fig. 2), which also showed the habitat types included within each MPA and the distance to closest sea grass and mangrove habitats (a proxy for provision for ontogenetic movements between habitat types performed by some species). These evaluation cards were used, in combination with information from management effectiveness assessments conducted at some sites, by participants at a second workshop in June 2015. Workshop participants were asked to form four breakout groups to discuss the design and management effectiveness of each of Pohnpei's MPAs. Each group used sticky notes to place each MPA along two axes ranging from poor to excellent (Fig. 3). A member of each group then presented back in plenary the rationale for their decisions. Dividing the summarized matrix into four quadrants indicated priority actions for different MPAs (Fig. 3). This exercise provided a structured focus for participant-led discussion, and allowed for stakeholder knowledge and experience to fill gaps in the management effectiveness data. The site-specific MPA evaluation cards have since been used to guide discussions with individual communities about how to improve the design of their MPA to provide adequate protection for focal species. For adaptive management to be successful in the long term, meaningful engagement with community-level stakeholders and consensus on MPA design revisions will be required, and this takes time. However, early indications are that using reef fish movement information to inform stakeholder-led design of MPAs will lead to improved outcomes for conservation and fisheries management in Pohnpei. The Palikir Pass marine sanctuary was formally designated in October 2015. At 12 km2, it is the largest MPA on the reefs surrounding the main island of Pohnpei. The initial proposal for this MPA covered less than half of this area. Following discussions about MPA adequacy for focal fish species, the proposed boundaries of the MPA were changed to ensure that they encompass key habitat types utilized by many species, and a known grouper spawning aggregation (Rhodes et al. 2012). As the first MPA to be established following the planning process described here, we are hopeful that this is indicative of a trend towards more adequate MPA design. Stakeholder involvement is known to be a key element in engendering natural resource management success (Gutiérrez, Hilborn & Defeo 2011). In a 2011 survey of 647 households in Pohnpei, >97% of respondents stated that participation in management decision-making was very important and that they were more willing to assist in monitoring and enforcement when they had a role in developing management strategies (Rhodes et al. 2011). We found that grounding discussions in particular species and locations of interest better engaged key stakeholders in the planning process and facilitated the articulation of local objectives for the MPA network (E. Joseph & E. Terk, pers. obs.). These were absent in previous planning processes, which focussed solely on regional objectives for biodiversity conservation. Workshop participants were better engaged during discussions about the adequacy of individual MPAs with which they were familiar, than the network as a whole. These discussions were facilitated by the availability of explicit, site-level criteria for protected area adequacy (c.f. network-level criteria, such as representativeness). When tasked with assessing the adequacy of Pohnpei's existing MPAs using information on the home range sizes of species they had identified as important, workshop participants all reported back that their MPAs were too small. This sparked discussion about how the MPA network might be redesigned far more effectively than presentations from conservation partners repeating generic 'bigger is better' guidelines. Evaluations of the design and management effectiveness of individual MPAs conducted by four breakout groups were remarkably concordant, with almost identical assessments for six MPAs, and minor disagreements for four. Stakeholders were content for not all species to be protected within all MPAs. Though this might be desirable from a conservation perspective, workshop participants stated that the specific objectives for some MPAs were to protect Cephalopholis argus and Siganus doliatus, which have relatively small home ranges. Explicit objectives are considered an essential component of conservation planning (Margules & Pressey 2000), and focusing on locally important objectives has been recommended as an approach to create local ownership of plans (Gurney et al. 2015). In reality however, objective definition can be an abstract or intangible concept for local stakeholders, resulting in the predominance of broad-scale, conservation-oriented objectives in conservation plans. Here, focussing on the ecological requirements of a subset of locally important species facilitated the articulation of local objectives for the MPA network, and generated realistic expectations of what might be achieved for different focal species. Further, information on which species are likely to be afforded protection within specific MPAs can be used to refine ecological monitoring protocols. The realities of implementation often constrain practitioners' ability to implement scientific best practice (Pressey et al. 2013), and this is true in Pohnpei. Though stakeholders understood that most of Pohnpei's MPAs are presently too small to achieve local fisheries management objectives, the difficulty in altering the boundaries of MPAs that have already been legislated was identified as a major obstacle to adaptive management to improve their adequacy. This is in contrast to customary governance systems, present within other Micronesian jurisdictions (Rhodes et al. 2011), which can allow rapid changes to protected area rules or boundaries in response to new information (Weeks & Jupiter 2013). With increased support from community members and contemporary traditional leaders, modifications to MPA design might be possible without changes to formal legislature, however. In addition to establishing new MPAs that afford better protection for focal species, individual communities are considering other possible mechanisms to improve the design of existing MPAs, for example by implementing larger seasonal closures that extend from the core no-take area. Nevertheless, even where they are large enough to encompass species' home ranges, the small size of most MPAs precludes the combination of essential habitat types required by many species during ontogenetic development, and most are not located to take feeding or reproductive migrations into account. This emphasizes the importance of understanding whether and how individual MPAs are connected to allow for larval dispersal and adult and juvenile migration between them. While workshop participants considered that MPAs did not need to protect the home ranges of bumphead parrotfish, as this species is protected through other legislative means, poor enforcement means that the effectiveness of this alternative management is questionable. Knowledge of which species are unlikely to be protected within MPAs might provide a basis for better integration of spatial and non-spatial fisheries management. Our assessments of effective MPA size are based on the assumption that all species inhabit exclusive home ranges. If available, species-specific information on how individuals' home ranges are distributed relative to one another could be used to determine how many individuals an MPA of a specific size could protect. We were unable to find this information for any of the focal species in our analyses; however, it could be established through telemetry studies of individual species' movements or derived from meta-analyses of fish densities within well-designed and effectively managed marine reserves (Green et al. 2015). Following the guidelines proposed in Green et al. (2015) led us to conclude that many MPAs in Pohnpei are too small to support fish populations that are, nevertheless, found within them. There are several possible explanations for this. First, populations might be present within MPAs due to the partial protection provided to individuals whose home range coincides with the no-take area, but in decline. Secondly, if the assumption of home range exclusivity is false, many more individuals may reside within an MPA smaller than twice their average home range size. Thirdly, home range sizes of some reef fishes are known to vary with habitat patchiness (Green et al. 2015). Nash et al. (2015) suggest that MPAs which encompass whole reefs isolated by open water may provide greater protection for fish populations than MPAs of equal size on contiguous reefs, due to the apparent reluctance of fish to cross open water. It has also been suggested that fishes may utilize smaller home ranges within MPAs. Given that decisions regarding MPA size represent a trade-off between affording adequate protection to focal fish species and allowing for extractive activities that underpin livelihoods and food security, this uncertainty needs to be resolved. A better understanding of how home range sizes vary with habitat type, quality, fragmentation and level of protection, for all species, is required for guidelines for adequate MPA design to be refined and applied with greater precision. In many contexts, social and economic considerations constrain the size at which protected areas can be implemented, making it impracticable to designate areas large enough to protect the full range of species occurring within a region. Information on how differently sized protected areas may benefit different species permits explicit evaluation of these trade-offs. Our case study demonstrates that this approach can also better engage local stakeholders in conservation planning, and influence local decision-making towards more adequate protected area design. Stakeholder-led discussions about protected area adequacy also led to more realistic expectations about what those areas can achieve, and monitoring protocols that target species predicted to respond to management. We used available information on the home ranges of coral reef-associated fishes to inform discussions with local stakeholders about the adequacy of MPAs in Pohnpei, Micronesia. The framework that we applied is generally applicable wherever animal movement data are available, however. Our approach could be further refined with data on the territoriality (or density) of focal species, and their relative vulnerability in protected and unprotected areas. Though adult movement is more straightforward to quantify than larval dispersal, present understanding of movement patterns of coral reef fishes remains far from complete. Data remain unavailable for many key species; for example, no movement data are available for caesionids, which are key fisheries species in parts of South-East Asia (Russ & Alcala 1998). Further ecological research effort, for example to understand how home range size varies with life-history phase, habitat type, quality, degree of fragmentation and level of protection, will benefit efforts to improve the adequacy of marine reserves for key fishery species. This is especially critical in developing countries, where dependence upon natural resources is high, constraining the size at which protected areas can feasibly be implemented. We are grateful to Ed Warner and an anonymous supporter for funding this work, and thankful to the conservation practitioners and stakeholders in Pohnpei who facilitated and attended the protected area network planning workshops. Comments from two anonymous reviewers improved the manuscript. Data have not been archived because this article does not contain data. Rebecca Weeks is a senior research fellow with the ARC Centre of Excellence for Coral Reef Studies; her research aims to improve conservation planning for marine and coastal ecosystems in the tropics. Alison Green is a senior marine scientist with The Nature Conservancy; she has 25 years' experience in coral reef conservation and management focusing on MPA design. Eugene Joseph is the Executive Director of the Conservation Society of Pohnpei; he has extensive experience working with and organizing local communities and is an expert on Micronesian reef fish. Nate Peterson is a GIS specialist with The Nature Conservancy; he has led and supported numerous conservation-focused GIS projects across the Pacific region over the past 9 years. Elizabeth Terk has worked on community-based conservation projects around Pohnpei for almost a decade, and is currently with The Nature Conservancy Micronesia Program.