Dispersal of Grouper Larvae Drives Local Resource Sharing in a Coral Reef Fishery
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Current Biology 23, 626–630, April 8, 2013 ª2013 Elsevier Ltd All rights reserved http://dx.doi.org/10.1016/j.cub.2013.03.006 Report Dispersal of Grouper Larvae Drives Local Resource Sharing in a Coral Reef Fishery Glenn R. Almany,1,* Richard J. Hamilton,3 Michael Bode,4 predict that 50% of larvae settled within 14 km of the aggre- Manuai Matawai,5 Tapas Potuku,6 Pablo Saenz-Agudelo,7,8 gation. These results strongly suggest that both local and Serge Planes,7,9 Michael L. Berumen,8 Kevin L. Rhodes,10 cooperative management actions can provide fisheries Simon R. Thorrold,11 Garry R. Russ,1,2 benefits to communities over small spatial scales. and Geoffrey P. Jones1,2 1Australian Research Council Centre of Excellence for Coral Results and Discussion Reef Studies 2School of Marine and Tropical Biology To rebuild and sustain coastal fisheries in developing nations, James Cook University, Townsville, Queensland 4811, nongovernmental and intergovernmental organizations have Australia advocated the use of a range of small-scale initiatives, 3Indo-Pacific Division, The Nature Conservancy, 245 Riverside including marine protected areas (MPAs) [6, 7]. Incentives for Drive, West End, Queensland 4101, Australia adopting and complying with such initiatives are naturally 4Australian Research Council Centre of Excellence for greatest when people are likely to benefit from their actions. Environmental Decisions, School of Botany, The University of For example, if fishers agree to protect a portion of their fishing Melbourne, Parkville, Victoria 3010, Australia grounds, will they benefit and/or will benefits flow to other 5Manus Field Office, The Nature Conservancy, P.O. Box 408, groups (i.e., positive externalities)? Logically, the key benefit Lorengau, Manus Province, Papua New Guinea of concern to fishers is the degree to which their actions 6Kavieng Field Office, The Nature Conservancy, P.O. Box 522, can contribute to the replenishment of their own fish stock. Kavieng, New Ireland Province, Papua New Guinea Fisheries replenishment depends on juvenile recruitment, 7USR 3278, EPHE-CNRS, Centre de Recherches Insulaires and fishes produce planktonic larvae that have the potential et Observatoire de l’Environnement, BP 1013, 98729 Moore´ a, to disperse widely before recruiting to benthic habitats. French Polynesia Thus, understanding the spatial scale of larval dispersal—the 8Red Sea Research Center, King Abdullah University of dispersal kernel—plays a critical role in determining which Science and Technology, 23955-6900 Thuwal, Kingdom of management strategies are viable, who benefits from manage- Saudi Arabia ment, and the degree of cooperation necessary among neigh- 9Laboratoire d’Excellent ‘‘CORAIL,’’ BP 1013 Papetoai, bors for the fishery to be sustainable [3–5, 8–11]. If most larvae 98729 Moore´ a, French Polynesia disperse far from a MPA, few will return to replenish the local 10College of Agriculture, Forestry and Natural Resource fishery, and fishers therefore have little incentive to adopt or Management, The University of Hawaii at Hilo, Hilo, comply with restrictions [8]. The likelihood of this undesired HI 96720, USA outcome increases as the spatial scale of larval dispersal 11Department of Biology, Woods Hole Oceanographic increases relative to the size of the local fishing ground. This Institution, Woods Hole, MA 02543, USA fact is particularly worrying for the many tropical nations where fisheries management occurs at the spatial scale of small customary marine tenure (CMT) areas, which often consist of Summary just a few hundred hectares of habitat [1, 12–14]. Recent advances are providing the first direct measurements of larval In many tropical nations, fisheries management requires dispersal [15–17] and the first direct estimates of how the a community-based approach because small customary probability of larval dispersal varies as a function of distance marine tenure areas define the spatial scale of management [18, 19] in small coral reef fishes, but we know little about larval [1]. However, the fate of larvae originating from a commun- dispersal in larger fishery species [but see 20]. Thus, whether ity’s tenure is unknown, and thus the degree to which and at what spatial scale communities can benefit from a community can expect their management actions to management are unknown. replenish the fisheries within their tenure is unclear [2, 3]. We used genetic parentage analysis to measure larval Furthermore, whether and how much larval dispersal links dispersal from a single fish spawning aggregation (FSA) of tenure areas can provide a strong basis for cooperative squaretail coral grouper (Plectropomus areolatus, Serranidae) management [4, 5]. Using genetic parentage analysis, we at Manus, Papua New Guinea. In 2004, to replenish local measured larval dispersal from a single, managed spawning fish stocks, fishers within a single CMT area established aggregation of squaretail coral grouper (Plectropomus a MPA protecting 13% of their fishing grounds, including the areolatus) and determined its contribution to fisheries studied FSA. We sampled this FSA over 2 weeks in May replenishment within five community tenure areas up to 2010 and collected tissue samples from, and externally 33 km from the aggregation at Manus Island, Papua New tagged, 416 adult coral grouper (235 females, 180 males, and Guinea. Within the community tenure area containing the 1 sex undetermined), which represented an estimated 43% aggregation, 17%–25% of juveniles were produced by the (95% confidence interval [CI]: 32%–53%) of the FSA popula- aggregation. In four adjacent tenure areas, 6%–17% of juve- tion (see the Supplemental Experimental Procedures available niles were from the aggregation. Larval dispersal kernels online). Over 6 weeks (November–December 2010), we collected 782 juvenile coral grouper from 66 reefs located within five *Correspondence: [email protected] CMT areas up to 33 km from the sampled FSA (Figure 1). Larval Dispersal and Resource Sharing 627 Figure 1. Location and Abundance of Sampled and Assigned Juveniles Spatial patterns of coral grouper (Plectropomus areolatus) (A) juvenile sample collection and (B) juvenile parentage assignments. Green (A) and yellow (B) circles are scaled to the number of juveniles. Adults were sampled from a single fish spawning aggregation (red cross), and juveniles were collected from 66 individual reefs (green circles in A). White dashed lines are customary marine tenure boundaries of the five communities, with the name of each commu- nity in white above in (A). Land is black, coral reefs are gray, and water is blue. See also Figures S1 and S2. Parentage analysis identified 76 juveniles that were the functional forms to these data, and we found that Ribbens offspring of adults sampled at the FSA (see the Supplemental and Gaussain kernels provided the best fit, with AIC weights Experimental Procedures), and these 76 juveniles came from of approximately 0.3. Randomization tests of goodness of fit 25 reefs (Figure 1). Assigned juveniles ranged in size from indicated that both models describe trends that would occur 62–288 mm total length and were between 94 and 394 days by chance with a probability of less than 8% (see the Supple- old (see the Supplemental Experimental Procedures). The mental Experimental Procedures). These two kernels agreed proportion of the juvenile sample collected from each CMT that at least 50% of larvae settle within 14 km of the FSA area that was assigned to adults sampled from the FSA was (Figures S1 and S2). A Ribbens kernel [21] provided the best significantly higher for Locha (the tenure area containing the fit and predicted that 50% and 95% of larvae settled within FSA) than for any other CMT area (p < 0.02 from a permutation 13 km and 33 km, respectively, of the FSA (Figure 2). The test) and lowest for Timonai, the CMT that is the most distant mean dispersal distance calculated from the Ribbens kernel from Locha (Table 1). We estimated the number of parentage was 14.4 km (see the Supplemental Experimental Procedures). assignments missed due to incomplete adult sampling Understanding whether, how much, and at what spatial (see the Supplemental Experimental Procedures), and the scale human communities can benefit from management expected mean percent of recruitment derived from the actions is key to designing effective strategies, obtaining and sampled FSA in each CMT area was as follows: Mbunai, sustaining support for management, and providing greater 13.1%; Pere, 13.9%; Locha, 19.6%; Tawi, 12.1%; and Timonai, incentives for compliance. Our results suggest that communi- 6.9% (Table 1). ties on Manus can indeed benefit from management, both Juvenile samples were collected from 66 reefs with known independently and collectively. Exactly how recruitment locations, and we calculated the Euclidean distance between benefits are distributed among communities will depend on each reef and the sampled FSA. We used the proportion of the locations of CMT boundaries relative to larval dispersal juveniles at each reef assigned by parentage analysis to patterns and spawning aggregations, but the shape of the sampled FSA adults to estimate the shape of the larval larval dispersal kernel in the present study suggests that dispersal kernel. Assigned juveniles came from 25 of the 66 the greatest recruitment benefits are retained within several reefs sampled, and assignment proportions from all 66 reefs kilometers of the larval source. Whether recruitment translates were used to estimate the dispersal kernel. We fit five directly to fisheries benefits requires further study, focusing Current Biology Vol 23 No 7 628 Table 1. Observed and Expected Parentage Assignments in Each Customary Marine Tenure Area Observed Expected Tenure Area Juvenile Samples Parentage Assignments % Assignment Parentage Assignments % Assignment (95% CI) Mbunai 79 7 8.9 10.4 13.1 (11.4–16.5) Pere 235 22 9.4 32.6 13.9 (12.1–17.4) Locha 204 27 13.2 40.1 19.6 (17.1–24.7) Tawi 221 18 8.1 26.7 12.1 (10.5–15.2) Timonai 43 2 4.7 3.0 6.9 (6.0–8.7) Total 782 76 9.7 112.7 14.4 (12.5–18.1) Adults were sampled from a single Plectropomus areolatus spawning aggregation located in the Locha tenure area.