Fisheries on coral reefs are multispecific and multigear. It can be very productive, but typically, there is little or no effective management (e.g., Carpenter and Alcala, 1977; Alcala, 1991; Cabanban and Biusing, this volume). As a result, around the South China Sea, there is widespread overfishing, destruction of ecosystem, and declining yields (e. g., Chou et al.., 1994; McManus, 1997; Chou, 1997). In the coastal waters of the Philippines area generally overfished to the point of having more than twice as much as fishing pressure as necessary for optimal harvests (McManus, 1995). Many reefs are badly damaged from dynamiting or fish bombing and characterised by low species richness and low biomass of commercially important species (Rubec, 1988). Reefs are dying as a result of fishing with cyanide (Johannes and Riepen, 1995). In Indonesia, destructive fishing (Pet-Soede and Erdmann, 1998) is damaging coral reefs. These effects on the reef are typical of many reefs in the region (McManus, 1997). Thus, proper management is acutely needed.
A number of management techniques have been tried but limited resources, large areas, dispersed landing sites, and poor fishers contribute to the difficulty in enforcement. Conventional methods, when applied to coral reef fisheries management is inappropriate because they require vast information on the biology of stocks and a huge budget for implementation and are difficult to enforce (Alcala and Vande Vusse, 1994; Berkes, 1994; Roberts and Polunin, 1993). A non-conventional method is the establishment of marine reserves - a method that is considered a viable alternative world-wide (Dixon, 1993; Dugan and Davis, 1993). Marine reserves offer protective management which has several benefits (Alcala, 1988), including the protection of spawning stocks, protection of biomass that provide larvae to replenish distant fishing grounds, and protection of juveniles and adults that emigrate to adjacent, unprotected areas. In contrast, marine reserves require minimal information on the biology of stocks and enforcement is relatively easy. However, the effectiveness of this approach depends on the agreement of a functional majority of the resource-users (Alcala and Vande Vusse, 1994; Berkes, 1994).
Despite these benefits from marine parks that were established around the world, very few studies have quantified these benefits for fisheries management (see review below). The Coastal Zone Management Programme at Universiti Malaysia Sarawak (UNIMAS) is researching into the benefits of reserves so that these advantages can be used to convince resource-users that there are real benefits to non-destructive fishing and to protection of areas. In particular, it has conducted a preliminary investigation on the benefit of a protected area, the Layang Layang in the Spratlys, in being a source of larvae that are exported by currents to other reefal areas. The results of this study demonstrate the value of small reefs as sources of larvae for other reefs in the South China Sea.
Marine reserves are important to fisheries management. They maintain biomass of large marine organisms and genetic biodiversity. They provide biomass of individuals to migrate to non-protected areas where they get recruited into the fishery. These benefits are reviewed and discussed below with reference to fisheries and aquaculture.
Large fishes that live on coral reefs such as groupers, snappers, emperors, and wrasses have either disappeared or become very rare due to overfishing in the South China Sea and in many coral reef areas in the Caribbean. These large, solitary, and frequently territorial fishes are at risk from simple artisanal overfishing and intensive capture of fishes for the live-fish trade in Southeast Asia (see related articles in this volume). The live fish trade has swept through most reefs in the South China Sea in an effort to satisfy the Hong Kong driven demand for large rare fish. Incentives are high when wholesale prices (in 1995) vary from $ 30-40 per kg for ordinary groupers, $ 40-60 kg for red-coloured groupers, and $60-90 for Napoleon wrasse (Cheilinus undulatus) or Polka dot Grouper (Cromileptes altivelis). Due to the live-fish trade, these fishes are currently classified as vulnerable although in many areas they are locally extinct although they have very wide ranges. This has prompted the inclusion in early 1996 of some of the largest fish species, Napoleon wrasse and bumphead parrotfish into the IUCN Red List.
The biggest of these fishes can only be conserved and protected effectively from overfishing by the use of protected areas. Protected areas have been proposed by some authors as the only solution to the overfishing problems (Birkeland, 1997; Russ, 1966) and reserves may be the only way to provide critical refuges for large and long-lived species (Huntsman, 1994) and those that undergo sex-change during growth (like the groupers). Sexually mature adult populations will be maintained in reserves and larval export to other reefs will continue to provide a supply of juveniles that can recruit to the fished population (see below).
Marine reserves are equally important in maintaining the genetic biodiversity of wild populations of large fish species. These wild populations are important to aquaculture of tropical marine fishes, which in its infancy, relies on wild-caught broodstock. The most fecund broodstock are the big ones that are genetically selected for fast growth, disease resistance, and large maximum size. These big individuals are fished preferentially for broodstock and are increasingly only available in reserves or in lightly fished areas. In any area, where fishing pressure is heavy enough to remove fish shortly after first spawning, there is actually an active reduction in natural selection for the attributes wanted by aquaculture broodstock. High levels of exploitation of wild population do not allow the genetic advantages of large final size to be expressed. This fisheries selection pressure towards earlier reproduction and smaller maximum size has been demonstrated for populations in the Caribbean and the Grand Banks (Man et al.., 1995).
Marine reserves are important for protecting the spawning stock of natural populations and broodstock for aquaculture. In protecting these populations, the biological attributes of high fecundity and fast-growth, stored in the genotype of big individuals, will be prevented from being lost. High fecundity is proportional to body size; the bigger the fish the greater is the fecundity. However, the fecundity of a big fish is not proportional to the weight of small individuals; a big fish produces almost twice as many eggs as the same weight of small fish. For example, one 12.5-kg large snapper produces the equivalent number of eggs as two hundred thirty three 1-kg snappers (Bohnsack, 1994). Thus, it is an evolutionary advantage that allows fish to grow as fast as possible to the maximum size, which the environment can support.
Similarly, fast growth is important in natural populations and in aquaculture. It limits the time an individual spends at a size that is vulnerable to predation, allowing it to reach a large maximum size and increasing fecundity levels. Having large parents gives the maximum genetic advantage to offspring such as valuable combinations of genes are passed on for rapid growth, large maximum size, disease resistance, and other survival characteristics that enabled the parents to attain large sizes in the hostile environment of the natural reef. Until there is a comprehensive series of reserves that are linked by larval transport, there is a strong argument for the adoption of a maximum size limit for exploitation as a way to protect some of the genetic diversity of the largest fish species.
The other large marine organisms that are heavily overfished and locally extinct are the eight giant clam (Tridacnidae) species which have been overfished for meat and shells throughout their tropical Indo-Pacific distribution (Lukas, 1994). The last 30 years have been particularly severe for the two largest species, due in part to international poaching for their adductor muscle. Low densities, erratic recruitment, and a relatively slow growth rate to reach harvestable size make these populations prone to overfishing. Even on the remote reefs of Layang Layang, population sizes for T. maxima indicate that the population is recovering from heavy fishing pressure in the past. Evidence of fishing pressure on stocks can be seen on most Indo-Pacific islands from the mean size of clams near a village compared with distant parts of the lagoon (Braley, 1989). In many areas, populations of T. squamosa are critically low and T. maxima are locally extinct. Declining giant clam stocks and local extinction's were a major stimulus for research into mariculture methods and there are several commercial farms now in operation.
Marine parks are important in conserving the genetic variability within populations if the population as a whole is to survive. Fished populations are especially at risk from genetic selection pressure; for example, size-selection of gear is a strong selective force for fishes with a small size-at-maturity. Furthermore, genetic variability is directly related to population size and population size at maximum sustainable yield (MSY) is generally only half the size of the unfished population. Populations of many fish and invertebrate species on many reefs in the South China Sea are well below MSY (McManus et al.., 1994) and are therefore at risk from loss of genetic biodiversity. Conservation of populations is thus necessary but it is unknown what minimum population size can maintain adequate genetic diversity and minimise the risks associated with natural disasters or parasites. It is likely though that the minimum population size is likely to vary between species to preserve genetic variability.
It has now been well established that marine reserves commonly support higher densities and larger sizes of heavily fished species than are found outside reserves. The abundances and average sizes of many larger carnivorous fishes are numerous and bigger within protected areas (Polunin and Roberts, 1993). In areas where smaller fishes are also targeted by fishers, species from all trophic levels show similar responses to reduction in fishing pressure. In the 2 years following the set up of the Saba Marine Park in the Netherlands Antilles, there was a 60% increase in overall biomass of commercially important families while the predatory snappers (Lutjanidae) increased by 220%. In comparative studies of coral-reef fish communities of Saba Marine Park and Hol Chan Marine Reserve (Ambergris Caye, Belize) in the Caribbean, 45 % of target species commonly recorded in visual censuses in Belize, and 59% at Saba, showed greater abundance, size or biomass in shallow protected sites (Polunin and Roberts, 1993). The greatest estimated biomasses were observed in locally protected snapper (Lutjanidae) in Belize and Saba, and grunt (Haemulidae) at Saba. In both protected areas, the local stock of visible demersal target fishes was 1.9 to 2.0 times greater in biomass and 2.2 to 3.5 times greater in commercial value than in fished sites. Similarly, in reserves in the central Philippines, fish abundance's and standing stock of highly fished species were significantly higher than in non-reserves and control sites.
In other places, there is evidence that marine reserves that allow limited fishing using traditional methods can still be beneficial. On the Kenyan coast, species richness was highest in marine parks where no fishing or collecting was allowed but the same was not true for fish abundance, or for biomass of commercially important fish (Samoilys, 1988). Some of the highest densities and weights of fish were recorded from the marine reserves where limited fishing using only traditional fishing methods was allowed. Areas with higher fishing intensity had smaller standing crops of fish, but not comparably smaller abundances.
Reserves clearly create a local increase in abundance and size of fishes after the elimination of fishing mortality, which in turn leads to greater egg production per unit of reef and greater export via pelagic dispersal to fishing grounds as well as spillover emigration to local reefs. "Spillover" of individuals across reserve borders has been shown for protected areas in the Philippines where there was a significantly increased fish yield from nearby traditional fishing areas (White, 1989). There are good reasons to expect such spillover from most reserves, and there is limited direct evidence for it (Rowley, 1994). However, the magnitude of any resulting increase in local catches will be difficult to predict and very difficult to measure.
The actual species that spillover will vary with behaviour. Many small coral reef fish are strictly territorial and have small ranges (Barrett, 1995). Territorial ranges approximately 100 by 25-m or less were found in six wrasse, and monocanthid species. The natural habitat boundary of open sand between the reef and adjacent reefs appeared to be an effective deterrent to emigration for these species. Other species notably the nocturnal squirrel and soldier fish as well as the carangids, grunts, and snappers are swim over a wide range and cross sandy areas of lagoon on a regular basis.
In general, field studies from widespread sites around the globe support predictions of increases in abundance and average size of fishes in protected areas but the manner in which reserves enhance larger-scale recruitment to fish stocks is difficult to quantify in the field. A meta-population computer model shows how marine reserves help to conserve reef fish populations and benefit fisheries (Man et al.., 1995). Simulations of the model show that reserves become highly beneficial as the local extinction rate caused by fishing becomes large because they provide a source of recruitment into fished-out patches. The abundance of the exploitable population and the sustainable yield is maximised when half of all patches (reserves + exploited patches) are occupied by the stock. In such circumstances, the introduction of reserves meets the needs both of conservation and of sustainable exploitation of the fishery.
Reserves can also allow coral reef recovery after ecosystem damage by cyanide or dynamite fishing. Reefs in the Philippines which have been protected after habitat destruction show evidence of recolonisation by corals and other sedentary benthic species (White, 1989).
Marine reserves are effective in maintaining high abundance in the reserve and higher yields of outside of the reserve (e. g., Alcala and Russ, 1990; Russ and Alcala, 1996). The proposed mechanism for the increase in yields is by emigration of juveniles and adults from the reserve to the fished site. Russ et al.. (1994) simulated this mechanism in a yield-per-recruit model for Sumilon Island Fishery Sanctuary, central Philippines. Later, circumstantial evidence of the export of biomass was shown from Apo Island, central Philippines from a long-term visual census data set and from data on fishery yields (Russ and Alcala, 1996).
To make marine reserves effective to enhance fishery yields, the location of marine reserves within the South East Asia region needs to be situated using two distinct types of reserves. There is a need for some areas to be located in middle/edge arrangement of biodiversity reserves, linked to biogeographical regions (Hockey and Branch, 1994). Such reserves would achieve conservation of both representativeness (middle) and high diversity areas (edge).
The sizes of biodiversity reserves should be as large as possible, to allow for the maintenance of populations of the largest reef species, and be located in areas where current flow is reasonable, to allow the export products of larvae are as widely dispersed as possible. There is also a need for a second tier of small reserves which cover approximately 20 % of all coral reef areas (McManus, 1995) for the specific purpose of improving and maintaining local yields of exploited species. Second-tier smaller reserves should be designed to maximise their benefit to adjacent areas while minimising their size. Important populations can be maintained in small reserves whose primary function is to supply recruits and spillover of adults to nearby fished reefs. Reserves of this nature would be ideal for giant clams were recommended by several authors be established in each Indo-Pacific lagoon to ensure continued reproductive success of the two most endangered species (Lucas, 1994). The other function of the secondary reserves is as stepping-stones for maintenance of genetic biodiversity. Populations of most marine organisms in minor reserves will be too small to maintain adequate genetic diversity, but having a series of reserves which are all interlinked by larval transport to the larger biodiversity reserves will limit loss of genetic information and will almost eliminate permanent local extinction of species.
There are several functioning examples of second tier reserves; the small island sites of Apo, Negros and Sumilon, Cebu, in the Philippines both have fringing coral reefs and support local fishers (White, 1989). In the province of Negros Oriental, blastfishing has been stopped, cyanide fishing in non-existent, and about 19 preserves are in place and working (CENTRO, pers. comm.). The sites have a community based marine resource management system. With management, the coral reefs are a significant resource, providing economic benefits that accrue to local fishers. These benefits include: (1) increased fish yields from traditional fishing areas; (2) increased fish diversity and abundance within sanctuary areas; (3) slightly improved coral substrate cover resulting from the use of less damaging fishing methods; and (4) increasing tourism.
Empirical evidence for the important role of marine parks as sources of larvae and recruits are limited. We report here a preliminary study of the role of good reefs in exporting larvae to downstream reefs. The study was conducted at Layang Layang, in the Spratlys, one of the reefs being claimed by Malaysia. It is distant from population centres and the only infrastructures on the Island are the Royal Malaysian Navy base and a dive resort. The presence of the Royal Malaysian Navy and the inaccessibility of the atoll result to the reefs not being fished actively and are isolated effectively from all other human influences such as pollution and habitat destruction. Thus, it remains a pristine, undamaged coral atoll with some of the best coral reefs in the world (Mackey et al.., 1997). It also has large spawning populations of many commercially important reef fishes and clams.
Larvae were collected in the waters arriving and leaving Layang Layang during the summer of 1996 (Oakley, unpub. data; Figure 1). Plankton nets with 508 micron-mesh and diameter of 50 cm were towed at 4 stations in the north, in the centre, on the reef, and in the south of the Island. Stations 1 and 4 are approximately 500 m North or South of the plankton stream. Stations 2 and 3 are in the plankton stream. Nets were towed obliquely at 2 knots from 10 m to the surface at 2 knots for 10 minutes. Horizontal tows were also at the same speed and duration. Larvae were preserved in the field and later counted in the laboratory.
The pattern of larval distribution in the waters around Layang Layang clearly demonstrated the export of larvae from the reefs (Figure 1). In the waters arriving on the atoll, there were almost no planktonic larvae of reef-based populations in the water. As the water passed through the reef, larvae of many reef-based species were released in the water, increasing the numbers of larvae in the water, and then carried away. Thus, the departing plankton stream has more larvae and could be clearly identified (Figure 2) although the direction of the stream changed in relation to wind and water currents (Figure 1). The majority of plankton were carried to the North West by the prevailing current although on calm days there was an additional wind driving surface flow to the East (Figure 3). It is possible that the larvae that travelled eastward eventually mixed with the predominant current and were carried back across the reef. This may be one of the mechanisms, which returns larvae to their natal reef. However, these larval export studies are only just beginning and more information will be needed before larval export models can be developed for Layang Layang.
These results from the study on from Layang Layang Reef are empirical evidence on the important role of protected reefs for fisheries although the Reef is not an established marine park. In effect, however, Layang Layang Reef, is a marine park due to the absence of exploitation and minimal developmental activity. The export larvae on the out-going tide and current from the reef provides evidence of the mechanism by which good reefs serve as sources of larvae.
Marine reserves have the potential to play an important role in fisheries management especially in regions where there is heavy overfishing and ecosystem destruction. Enforcement of regulations in the region has proved to be almost impossible, cyanide fishing for the live fish trade (Johannes and Riepen, 1995) and dynamite are both banned but continue to be used on a regular basis. The fishers often know the effects their fishing is having but cannot stop because of the need to provide food and the feeling that the common resource has to be taken before it disappears. Community based management with its own enforcement can eliminate the problem of the common resource and can function as an important step to conserve biodiversity and local areas. Unfortunately, protection of vulnerable species and maintenance of resources is only likely to be successful if networks of reserves are established throughout the region to link larval supply and settlement areas.
Figure 1. Plankton exports during the summer months from Pulau Layang Layang in the Malaysian Spratly Islands. The wind driven surface flow to the E was only visible in calm sea conditions. Both plankton streams were clearly detectable 1km from the reef.
Figure 2. Higher plankton concentrations (organisms per 100 ml) to the West of Pulau Layang Layang in Stations 2 & 3 in the plankton stream and than in Stations 1 & 4 that are approximately 500 m to N or South of it. Samples were from oblique tows in Stations 1, 2, and 4 are approximately 1 km W of reef while Station 3 is approximately 500 m W.
Figure 3. Decreasing plankton concentrations (organisms per 100 ml) with depth to the East of Pulau Layang Layang from horizontal plankton tows. Samples were all taken in the middle of the stream.
Although success with village-based marine reserves (White, 1989; Russ and Alcala, 1994) in the Philippines indicates that local coastal management may be more realistic than that based solely on national regulations, there remain some problems in its implementation depending on the locality and situation. Problems with marine parks in Indonesia and Papua New Guinea show that local systems only work until there is foreign or industrial style fishing competing for the same resource (Johannes and Riepen, 1995). Marine reserves are difficult to establish and manage locally if the reefs in question are remote or out-of-sight of the community (Arquiza and White, 1994).
The planktonic larvae produced within the Spratly islands may be drifted around the South China Sea (McManus, 1994). Using the speed and direction of predicted water currents and from information on planktonic larval life, McManus (1994) calculated that larvae from the Spratly islands could travel to many of the heavily fished coastal reefs of the region. This theory is based on the knowledge that planktonic or pelagic larvae remain in the water column for periods that vary from a few days to a few weeks (Thorson, 1971; Cameron, 1986) for most invertebrates although several commercial lobster species have long planktonic lives (Sims and Ingle, 1966). Coral reef fishes, for example, have a variable duration of planktonic and pelagic phase but some do stay in the plankton for up to 100 days (Leis, 1991; Brothers and Thresher, 1985). However, even for larvae of schooling species, the eggs and early larval stages are almost certainly truly planktonic and a significant proportion of eggs and larval fish are carried away from reefs.
The results of the study from Layang Layang, in the Spratlys, provide empirical evidence or larval export from the Spratlys. Furthermore, it showed that the direction of the larval export could depend on the prevailing monsoonal winds and current that prevail in the South China Sea. It thus supports the hypothesis that the coral reefs in the Spratlys can be sources of recruits for depleted reefs around this marginal sea (Figure 1).
Spratlys as a Marine Park
The Spratlys, a group of islands in the South China Sea, are surrounded by coral reefs that are still in excellent condition (unpub. data). Brunei, China, Malaysia, Philippines, Taiwan, and Vietnam are claiming these islands in whole or in part. It is understood that China occupies currently seven of the Spratly reefs, the Philippines around 12, the Vietnamese no less than 27 reefs, Malaysia 4 reefs, and Taiwan and Brunei one each (Scholes, 1995). The belief that the seabed adjacent to this group of islands and reefs contain oil and gas and the strategic significance of the islands for sealane defence, interdiction, and surveillance (Valencia et al.., 1994) drive the claims to parts of the Spratlys.
Layang-Layang Reef, in the Spratly Islands, can serve as the "source" of larvae and juveniles for reefs with depleted populations of target species. The Reef has populations of common species at densities up to 15 per 100 m2 that is higher than most reefs surveyed by us (unpub. data). Large groupers are still being caught in the vicinity of Layang Layang in the South China Sea. A recent example was an individual, measuring over 3 m long and weighing approximately 230 kg. This individual has the potential of carrying the genetic potential for large size and the potential to produce eggs equivalent to 523 one-kg fish. A fish of this size are naturally rare in shallow depths (40 m and shallower) and was not observed by us but by Filipinos who were known to fish down to 60 m. Layang-Layang is thus worth conserving.
As a whole, the Spratly Islands were considered worthy of conservation (Gomez, 1994; McManus, 1994). It is an ideal biodiversity reserve as it is in the centre of global tropical marine biodiversity. It is ideally situated because no indigenous population live in the region and it is fished except to satisfy the live fish trade. A Marine Park for the Spratly Islands was already proposed earlier for conservation (Gomez, 1994; McManus, 1994). This arrangement requires a moratorium among the claimants in the Spratlys and limits further development while various options to resolve the conflict are being considered in the region. One of the proposed options is a United Nations-sponsored marine protected area with zones and rights assigned in a similar manner to the Great Barrier Reef Marine Park or Antarctica (Gomez, 1994; McManus, 1994).
With a marine park in the Spratlys, regulatory measures on fishing may be implemented to conserve the fishery resources that threatened by overfishing and habitat-destruction. Environmentally destructive fishing methods, currently uses, need to be banned and less destructive methods can be used to harvest the productivity of the Spratly reefs. Indeed, if we could persuade fishers to target medium-sized fishes, we could harvest a far greater biomass (10 to 20 times) for the same effect on the fecundity of the population (Birkeland, pers. comm.). Fishers could catch to the maximum sustainable yield without affecting population genetic potential since most species are recruitment-limited. This is a strong argument for not catching a few large individuals that could produce as many eggs as possible and enhance recruitment. Fortunately, protective management for coral reefs has this and other several advantages. Hopefully it will not be essential to fully understand the variable nature of recruitment and yield relationships before steps can be taken towards establishing a series of protected areas where fish stocks can recover from overfishing and habitat destruction.
Larval export from reserves or unfished reefs like Layang Layang in the Spratlys has the potential to supply recruits to reef fisheries over large regions, like the South China Sea. The success of marine parks for fisheries enhancement will depend upon many factors, including the knowledge of movement patterns and habitat requirements of all life stages (larval, settlement, juvenile, adult, feeding, and breeding) for each targeted species. This is clearly a difficult task when there are over 300 species of fish and invertebrates represented in Southeast Asian fish markets. As a step towards this goal, information on relative rates of production inside and outside reserves (Bohnsack, 1993), and patterns of larval transport and mortality, are being collected by the UNIMAS project to determine whether they may play a role in enhancing or sustaining catches in fished areas. Egg production in reserves and non-reserve areas will be estimated from knowledge of population structures and behaviour of the species concerned. The information from these studies will be useful in designing more effective marine reserves and to demonstrate conclusively the value of reserves on fisheries.
Coral reef areas with high standing stock of targeted species are important in replenishing not reefs open to fishing but also those reefs protected from fishing. Even reefs that are protected from fishing, such as the Saba Marine Park (Netherlands Antilles), has low population densities of groupers, perhaps due to a lack of supply of larvae from unprotected source areas (Roberts, 1995). Clearly, a "source" reef, like Layang Layang, is important in replenishing viable populations even in protected areas.
Marine parks are important and beneficial not only for tourism and education. These parks play an important role in aquaculture and fisheries. In order to retard the impacts of anthropogenic uses of the reefs, particularly exploitation of living resources, more marine parks need to be established to for sustainable fisheries.
We are deeply indebted to the Royal Malaysian Navy, for permission and logistical support to conduct research on Pulau Layang Layang. Sarawak Shell Sdn. Bhd., our long- term supporters of marine conservation at UNIMAS, has contributed financially towards this research on Pulau Layang Layang. Others who have contributed include the Layang Layang Resort, the team members from the University of Aberdeen 1996 Expedition and Esso Malaysia Sdn. Bhd. This work could not have been completed without the support and encouragement of Prof. Ghazally Ismail, Deputy Vice Chancellor Universiti Malaysia Sarawak. This work was partly funded by UNIMAS research grant 89/96(8), for which we are very grateful.
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