07 Tupper FB105(4)

Spillover of commercially valuable reef fishes from marine protected areas in Guam, Micronesia Item Type article Authors Tupper, Mark H. Download date 26/09/2021 07:56:17 Link to Item http://hdl.handle.net/1834/25510 527 Abstract—Does adult spillover (move- Spillover of commercially valuable reef fishes ment out of marine protected areas [MPAs]) of fish create a net export of from marine protected areas in Guam, Micronesia fish biomass from MPAs to adjacent fished reefs? Biomass of five commer- cial reef fish species was estimated Mark H. Tupper by visual census within and outside Email address: [email protected] three MPAs in Guam, Micronesia. The WorldFish Center (address for correspondence) For most species and sites, biomass Jalan Batu Maung, Batu Maung was significantly higher within the 11960 Bayan Lepas MPAs than in adjacent fished sites. Penang, Malaysia Movement of fishes into and out of the MPAs was determined by mark- and recapture experiments, in which Marine Laboratory fishes were tagged both inside and University of Guam, UOG Station outside of MPAs. Four out of five Mangilao, Guam 96923 species studied showed little or no net movement out of MPAs. However, the orangespine surgeonfish (Naso lituratus) showed a net spillover of biomass from all three MPAs; 21.5% of tagged individuals and 29% of the tagged biomass emigrated from MPAs. Over the past two decades, marine include random movements of fish Patterns of spillover were strongly protected areas (MPAs) have been during their routine activities (some- influenced by physical habitat barri- increasingly adopted as an important times referred to as diffusion), emi- ers, such as channels, headlands, or fisheries management tool. The pri- gration in response to density depen- other topographic features. MPAs that mary goals for MPAs are to protect dence (e.g., Tupper and Juanes, 1999; are physically connected by contigu- critical habitat and biodiversity, to Abesamis and Russ, 2005), directed ous reef structures will likely provide sustain or enhance fisheries by pre- dispersal due to migration, and onto- more spillover to adjacent fished sites than those that are separated by habi- venting spawning stock collapse, and genetic habitat shifts (Gerber et al., tat barriers. This study demonstrates to provide recruitment to fished areas 2005). In order for spillover to effec- that MPAs can enhance export of fish (Gell and Roberts, 2003; Halpern, tively enhance adjacent fisheries, the biomass to fished areas, but spill- 2003). Enhancement of fished areas net direction of these movements, and over is species-specific and depends may occur through transport of larvae the number and size of fishes mov- on factors such as species size and from spawning stock within the MPA ing, must result in a net flow of bio- mobility. (Gerber et al., 2005) or by a net emi- mass out of the MPA. Measuring the gration of adult fish to adjacent fished movement of biomass into the MPA areas—a movement that is commonly should therefore be equally important known as “spillover” (e.g., Alcala et to measuring outward movements. al., 2005; Abesamis et al., 2006; Goni However, few studies have measured et al., 2006). immigration, and therefore net spill- The role of spillover in determin- over, and those that do address bi- ing MPA effectiveness has been ad- directional movements have reported dressed in both theoretical modeling conflicting results, depending on the studies (e.g., DeMartini, 1993; Kram- species or life history stage, the habi- er and Chapman, 1999; Gerber et al., tat, and the size and placement of the 2005) and in empirical studies. The MPA (e.g., Kelly and MacDiarmid, latter involve indirect documentation 2003; Zeller et al., 2003; Tremain et of spillover inferred from increases in al., 2004; Goni et al., 2006). fish biomass or catch per unit of ef- The degree of spillover from MPAs fort (CPUE) in adjacent fished areas depends on the rate of fish migration (e.g., Russ and Alcala, 1996; Roberts across MPA boundaries (DeMartini, et al., 2001; Tupper and Rudd, 2002; 1993; Gerber et al., 2005). Larger or Alcala et al., 2005), and direct docu- more mobile species with large home mentation of fish movement through ranges may spend too much time out- mark-recapture or sonic tracking ex- side of the MPAs to be effectively pro- periments (e.g., Chapman and Kram- tected, whereas smaller, more seden- Manuscript submitted 21 November er, 2000; Meyer et al., 2000; Kaun- tary species with small home ranges 2005 to the Scientific Editor’s Office. da-Arara and Rose, 2004; Meyer and may not cross MPA boundaries in Manuscript approved for publication Holland, 2005). There are a number sufficient numbers to enhance adja- 2 July 20007 by the Scientific Editor. of ways in which movement across cent fisheries by spillover (DeMartini, Fish. Bull. 105:527–537 (2007). MPA boundaries may occur; these 1993; Tupper and Rudd, 2002). If the 528 Fishery Bulletin 105(4) goal of a MPA is to enhance local fisheries by spillover any or all penalties applicable under the law. This study in addition to conserving spawning biomass, then it was conducted in 2003−04 at three MPA sites (Achang must be designed and situated so that net movement Reef Flat Marine Preserve, Piti Bomb Holes Marine of fishes from the MPA to fished areas can take place. Preserve, and Tumon Bay Marine Preserve—hereafter In most tropical island nations, enhancement of local referred to as Achang, Piti, and Tumon, respectively) on fisheries by adult spillover may be critical for contin- the western and southern coasts of Guam, Micronesia ued support of the preserve system by the local fishing (Fig. 1). All three sites consist of shallow reef flats that community (Russ and Alcala, 1999; Galal et al., 2002). lead seaward to a reef crest and then drop off to a reef In general, arguments for larval spillover carry little slope. The two remaining marine preserves, Sasa Bay weight with fishermen because dispersal may not occur and Pati Point, were not surveyed. Sasa Bay is a man- on spatiotemporal or “visual” scales that are meaning- grove swamp with no coral reefs within its boundaries, ful to them (Russ and Alcala, 1996; Russ, 2002; Abesa- and Pati Point is located within a restricted military mis et al., 2006). This situation is doubtless the case area (Anderson Air Force Base). in Guam, where little is known about the movement of The Achang preserve is the largest of the three pre- fishes on coral reefs. serves (4.8 km2). It includes a wide variety of habitats: One characteristic of heavily exploited reefs is the mangroves, seagrass, sand, coral, and three channels very low abundance (in some cases virtual absence) of that cut through the fringing reef from the outer reef large carnivorous fishes, particularly groupers (Ser- slope to the reef flat. The largest of these, Manell Chan- ranidae) and snappers (Lutjanidae) (Russ, 1991, 2002; nel, separates Achang reef flat from Cocos Lagoon, to Medley et al., 1993). In Guam, grouper biomass is no- the west of Achang Reef Flat. To the west, the reef flat ticeably lower than at the less heavily populated islands narrows and is interrupted by a rocky headland. Refer- in Micronesia (e.g., Palau). Much research has therefore ence fished sites for the Achang Preserve were located been directed at determining the effects of implement- in Cocos Lagoon. Seasonal traditional fishing is permit- ing MPAs on populations of large predatory fishes (e.g., ted in the Achang Preserve for juvenile streamlined Russ and Alcala, 1996, 2004). In Micronesia, however, spinefoot (Siganus argenteus), juvenile fusiliers (Pter- herbivorous fishes, particularly surgeonfishes and uni- caesio tile), and big eye scad (Selar crumenophthalmus) cornfishes (Acanthuridae) and parrotfishes (Scaridae) under special permit. are equally important to local fisheries, and in many The Piti preserve covers 3.6 km2 and consists of a areas they have dominated the catch (Amesbury et al., broad reef flat (1.4 km2) in Piti Bay bordered by Tepun- 1986). Thus, it is important to understand the effects gan Channel to the west. The fringing reef is continu- of MPAs on herbivorous and carnivorous fishes. ous from Piti Bay eastward to the fished sites at Asan To address whether MPAs in Guam can increase fish Bay. The reef flat includes unique features known as biomass and provide spillover to adjacent reef areas, “bomb holes,” which provide sheltered areas of deeper biomass of five important reef fish species inside three water. The deepest of these sinkholes were 9−10 m deep MPAs in Guam and on adjacent exploited reefs was and were densely populated by a variety of hard and determined by using underwater visual census. Net soft coral species. They host rich soft coral communities movements of both herbivorous and carnivorous reef and fish and invertebrate assemblages not often found fish across MPA boundaries were determined by using within the reef margin. The main sinkhole is occupied mark-recapture experiments. by an 11-m in diameter underwater observatory that was completed in 1996. It is also frequented by com- mercial scuba divers during diving tours (up to 200 Materials and methods divers a day). Fish feeding is a common practice around the observatory; therefore, our survey sites were located Study sites away from the sinkholes in order to minimize possible confounding effects of fish feeding and diver presence. In May of 1997, the Guam Department of Aquatic and The Tumon preserve lies adjacent to the central tour- Wildlife Resources (DAWR) established a network of five ist district on Guam. It is 4.5 km2 in total area and con- MPAs, termed “marine preserves,” around the island, sists of extensive reef flats (2.7 km2), a gently sloping which accounted for 11.8% of Guam’s shoreline and fore reef slope, and a broad shelf habitat.

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