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3.1 Federated States of Micronesia (FSM)

3.1.1 Background

FSM comprises of four states which together have a small (less than 100,000 in 1988) but rapidly increasing (3% annual growth) population. The economy is predominantly based on subsistence, the cash economy being largely restricted to government activities, where the minimum wage is about 80c per hour and an average income is US$ 2000 to US$ 3000.

The National Development Plan (1985–1989) identified FSM's marine resources, principally those of its 1.2 million square mile EEZ, as the country's major renewable commercial resource (FFA et al. 1988). Foreign licenced vessels exploit the pelagic and deepwater resource which is mainly tuna. The inshore reefs and lagoons support the subsistence fishery in which “all households are involved” (FFA et al. 1988) and the small domestic commercial market. There is some export of shallow reef fish to Guam, and deep bottom fish to Hawaii. Inshore resources are under increasing pressure from commercial exploitation (FFA et al. 1988).

Each state, through its Marine Resources Division, has control over the fisheries within its 12 mile territorial limit. The National Marine Resources Division is responsible for resources and fisheries within the 12 to 200 mile zone, as well as for coordination between states, and for provision of information and advisory services.

Numerous aquaculture developments have been suggested for Micronesia, ranging from population enhancement of native species, and the introduction of exotics, to the construction of a US $1.3 million National Aquaculture Centre.

Aquaculture activity in Micronesia has included the construction of ponds for mullet, milkfish, rabbitfish and Macrobrachium, trial farming of seaweed, sponge, and pearl oysters, and hatchery rearing of giant clams. Only the farming of the seaweed Eucheuma has been commercially successful.

The green mussel was not mentioned in connection with Micronesia in the 1984 review of Pacific Islands aquaculture (Uwate et al. 1984). It was however, included in a later review along with Trochus, green snail, oysters, milkfish, rabbitfish, mangrove crab, freshwater prawns, seaweed and sponges, as a subject for immediate aquaculture research since it “could become a good source of protein for the people of Micronesia” (Croft 1987). Micronesia is currently considered to have “a ready market in Guam and Saipan for frozen or fresh green mussels and local Micronesians traditionally eat a smaller relative … that is found here” (M. Gawel pers. comm.).

3.1.2 Site Surveys

The inshore waters around the high islands of Pohnpei and Kosrae have the highest potential phytoplankton biomass yields in Micronesia (Cowan and Clayshulte, 1980). This results from the very heavy rainfall carrying nutrients from the land into the near-shore waters. The longer residence time of the water in the larger lagoon around Pohnpei should lead to a greater phytoplankton build-up than would be possible within the narrow fringing reef around Kosrae (Birkeland et al., 1980). The resource atlases for Kosrae and Pohnpei (U.S. Army, 1987), together with the local knowledge of the staff of Marine Resources Divisions, were used to identify sites for subsequent visual inspection. Kosrae (Figure 1)

Most of the island is surrounded by a narrow fringing reef with open oceanic water and exposure conditions unsuitable for growing green mussels. The wider reef flats along the northwest coast between Okat and Walung offer sufficient protection for the establishment of submerged cultivation systems. However, except for the channels through the reef (e.g. the Molsron Okat) and holes in the reef, such as the hole 0.75 km south of the Molsron Okat (Kosrae Coastal Resources Atlas, Map 16) these areas are too shallow for either vertical or horizontal rope cultivation systems. Also, the water clarity in these areas and the prolific coral growth indicated a low productivity oceanic regime unlikely to be sufficiently productive for mussel cultivation.

On the east coast, the inner part of Lelu Harbour, within 0.5 to 1.0 km of the Marine Resources Division headquarters (KCRA, Map 3), has areas with over 5 m water depth suitable for hanging culture. The green turbid nature of the inner harbour water indicates high phytoplankton levels as a result of nutrient input from the adjacent mangrove areas. A hanging culture site in this area would have to be chosen to avoid conflict with navigation rights and minimise risk of pollution from Lelu township.

The coastal region likely to have the highest primary productivity on Kosrae is the Lelu Nefalil - Lelu Utwa lagoon on the south coast (KCRA, Maps 9 & 10). However, it is mostly shallow coral reef with a shallow and narrow entrance limiting water exchange and it is logistically remote. Pohnpei (Figure 2)

Pohnpei is surrounded on all sides by a barrier reef enclosing a wide lagoon, 5 to 10 km wide around the northern and western coasts. The lagoon waters are, typically, the low-productive oceanic type. The only areas likely to be sufficiently productive for green mussels are the mangrove-fringed embayments. Sokehs Harbour was investigated as an example of a mangrove-fringed embayment. The inner reaches of the Harbour appear to offer suitable depth and firm substrate for hanging and seabed cultivation of green mussels, with the natural fauna (presence of Anadara, poor growth of corals) and flora (extensive seagrass beds) indicating relatively turbid and thus high productive water (Pohnpei Coastal Resource Atlas, Map 19). Only a small area of reduced salinity (20 to 25%) was detected close to the mouth of the main stream running into the bay.

3.1.3 Potential for Green Mussels in FSM

The low productivity of the inshore waters around both Pohnpei and Kosrae will limit the opportunities for green mussel cultivation. Except in highly enclosed embayments and areas immediately adjacent to nutrient input sources and/or typical fringing mangrove forests, there is insufficient phytoplankton production to support dense aggregations of filter feeding bivalves in suspended cultivation. Areas of higher productivity, indicated by more turbid, greenish coloured water, do occur all around Pohnpei, and to a lesser extent around Kosrae. Such areas tend to be small and localised, but are typically shallow, with reduced water movement, are liable to salinity fluctuations, are frequently remote and have difficult access.

In many of these higher productivity areas the substrate may also be unsuitable for establishing benthic populations of mussels, since the resource maps indicate the presence of deposit feeders such as beche-de-mer, and also filter feeders that are adapted to cope with high concentrations of suspended solids e.g. Anadara species.

Figure 1

Figure 1. Map of Kosrae, FSM.

Figure 2

Figure 2. Map of Pohnpei, FSM.

3.1.4 Alternatives to Green Mussels

Eucheuma has been farmed at sites around Pohnpei. Some 14 mt of dried weed was exported to Denmark in 1987/88. The market has been estimated at up to 10,000 mt per year at US$ 300 to US$ 400 per mt. Seaweed farming, by government agencies, currently occupies only 15 ha of the 75 ha considered suitable around Pohnpei, with perhaps a further 400 ha of suitable area on other islands (P. Harris, pers. comm.). Other seaweed species may also be suitable for farming in FSM.

Recent trials have also shown that using similar techniques to those used for seaweed, sponge farming could be farmed and made commercially viable (R. Croft, pers. comm.).

Trochus is a commercially important but a heavily over-fished species. The most recent season saw a harvest of 258 mt in 3 days, compared to less than 200 mt over a 3 week season 2 years before. The sustainable yield has been estimated at 100 mt (M. Gawel, pers. comm.).

The Green snail Turbo marmoratus is currently under investigation as a potential species for introduction into Pohnpei and Kosrae (Yamaguchi and Kikutani, 1989).

Black lipped pearl Pinctada margaritifera is an indigenous species in FSM and farming for pearl production has been attempted in Pohnpei (Uwate et al., 1984).

All the species mentioned above have been previously identified as having aquaculture potential for Micronesia. All require further government support in varying degrees if they are to be successful. The support required ranges from extension work; to demonstrate seaweed and sponge farming techniques, to research; on the effects of enhancement of Trochus populations, or the impact of the introduction of green snail, to development; of viable farming techniques for pearl oysters.

All these species are more suited than the green mussel to the predominantly tropical oceanic waters of FSM. They all have the advantage of a non-perishable end product that does not require expensive, and frequently unavailable, freezer storage, and thus can be accumulated slowly, stock piled and collected for marketing at irregular intervals.

A part from the value of their shells, Trochus and green snails can provide edible protein, though the giant clam is a much more traditional and valuable protein source. Giant clam Tridacna spp. rearing is currently being investigated at Lenger Island on Pohnpei, where brood stock have been held and spawned and juveniles on-grown in a shore-based facility. All aspects of out planting of juvenile clams and enhancement of natural populations require further research and monitoring.

Another indigenous shellfish which is already part of the subsistence fishery but may have potential for increased protein production through enhancement or farming techniques is the mangrove or blood cockle Anadara. These species are already cultured in the tropics (Broom, 1985) but research into the biology of local species would be required.

3.2 Papua New Guinea (PNG)

3.2.1 Background

Papua New Guinea is a nation of great natural resources. Agriculture and, more recently, mining have been and continue to be the main contributors to the cash economy that supports the population of 3.5 million. Fisheries are not well developed and contribute insignificantly to either the formal economy (1 % of total export earnings in 1987) or to the subsistence economy, except possibly in coastal areas.

A recent comprehensive review and detailed study of the fisheries sector in PNG (UNDP, 1988) identified the fisheries resources contained in the 2.3 million sq. km of PNG's 200 nautical miles Declared Fisheries Zone, and assessed their potential. Policies, objectives and strategies for fisheries development were proposed. The review stated that “there is no tradition of either aquaculture or mariculture and there are currently no commercial activities in the field”, but commented that “the potential yields from aquaculture are limited only by the availability of suitable sites, suitable species for culture, economic inputs, technical feasibility and management expertise”.

The responsibilities of the various national and provincial agencies in the fisheries sectors are detailed in the UNDP (1988) review; only the observation that there is a lack of trained personnel with the relevant skills for managing the development of aquaculture, needs to be reiterated here.

The review (UNDP, 1988) emphasised the importance of the sedentary resources, such as Trochus, green snail, mother of pearl, beche-de-mer and giant clam, which together constitute the second most valuable fishery export, after prawns. The sedentary resources are particularly important to coastal villages where they may provide the only source of cash income. These sedentary resources include species with aquaculture potential.

Aquaculture activities in Papua New Guinea have concentrated on freshwater fish production, mainly carp and trout in the highland areas, but with some commercial attempts at shellfish farming. PNG aquaculture has been extensively documented 39 keyword references are cited in the PNG Fisheries Bibliography (Lock and Waites, 1985) and frequently reviewed (Von Pel, 1956; Kearney, 1976; Munro, 1976; Bardach, 1977; Kan, 1979, 1983; Delmendo, 1979; Mastaller, 1983).

Despite having a 5-year aquaculture development proposal (UNDP circa, 1980), which was subsequently modified by Kelleher (1981), the history of commercial shellfish aquaculture in PNG has been one of failure.

Experiments and trials with various indigenous edible oyster species led to small harvests in the mid-1960's but no subsequent commercial development occurred.

Two commercial pearl culture ventures operated in PNG in the 1970's; a technologically sophisticated Australian-Japanese enterprise at Port Moresby and a village-level artisanal farming venture, based in the Milne Bay area.

Clam husbandry is the only traditional form of shellfish aquaculture in PNG (Maclean, 1978). Research conducted at the University of Papua New Guinea's Motupore Island Research Station (Munro et al., 1983) and subsequently continued and expanded at ICLARM's Coastal Aquaculture Centre in the Solomon Islands, has provided the basis, yet to be exploited for commercial development, for clam farming in PNG.

Mussels, the only other shellfish mentioned in the Papua New Guinea section of the review of Pacific Islands aquaculture (Uwate et al., 1984), were considered to have “unknown” potential for culture. Kearney (1976) suggested awaiting the outcome of the FAO/UNDP programme on the introduction of Perna viridis into Fiji.

3.2.2 Site Surveys

Statistics derived from the UNDP (1988) reviews provide some indication of the physical potential for coastal aquaculture in Papua New Guinea, namely a coastline of about 10,000 km, including some 600 islands, and a coastal shelf, mostly reef associated, with less than 30 m depth of water, covering about 4 million hectares.

The 3 localities designated for site surveys by Fisheries Division each had some history of aquaculture activity. Milne Bay Area (Figure 3)

The Milne Bay Fishing Authority (MBFA), jointly operated by the national and provincial governments, is currently involved in the utilisation of local sedentary resources which include green snail, giant clam, Trochus, black lipped pearl and beche-de-mer. MBFA suggested an inspection of Sariba Island as an example of the type of coastal environment available in the province for mussel farming.

The northern coastline of Sariba Island has wide coral flats, as well as large mangrove-fringed embayments. The embayments provide extensive sheltered areas of water at reasonable depth (> 5 m), which appears from its deep green colouration to have a high level of primary production. The seabed in the embayments was said to be of “sandy mud” between the coral outcrops, and therefore suitable for moorings. These areas appeared suitable for suspended culture of bivalves.

Both Labu Labu Bay and Wanatonoli Bay offer a choice of sites ranging from areas with maximum shelter and highest productivity; but with the lowest water movement, at the heads of the embayments, to areas with less shelter and clearer water with lower productivity, but with better water circulation, towards the open sea. Optimum mussel cultivation conditions would need to be determined by trials at a number of sites.

The southern coastline of Sariba Island is rocky with a narrow fringing reef and exposed to the southwest trade winds. It is unsuitable for mussel farming.

The success of the pearl oyster farming activities during the 1970's indicates that the primary productivity of the coastal waters, at least in some areas is sufficient for intensive bivalve culture.

The logistics of servicing culture trials, particularly if surface suspended equipment is used, should be a major factor in the choice of sites, considering too the effect of traditional fishing rights and adjacent land use on the potential of the site or commercial aquaculture development. Potential commercial mussel farming operations should be aware of the financial problems which led to the collapse of pearl farming in the Milne Bay area, in order to avoid a similar failure. Fairfax Harbour, Port Moresby (Figure 4)

The site of the Australian - Japanese pearl culture farm, which operated during 1965 to 1970, at Idumava Point was visited. The site is surrounded by a large area of relatively sheltered water, much of which is between the shallow coral reef flats of suitable depth (> 5 m) for suspended culture. The thick green colouration of the water indicates high primary productivity. Much of the upper harbour is fringed with mangroves. Recent heavy rainfall may have contributed to the apparent high productivity of the water.

Data on water temperature and salinity, types of plankton, and oyster growth rates, which were collected during the pearl farming operation (Anon, 1970), would have been useful in evaluating this site for mussel farming. The data is not available, but the results from a concurrent study of edible oysters (Crassostrea spp) in other parts of Port Moresby Harbour indicate surface water temperatures in the range 25 to 30 degrees Celsius and salinities of 33 to 38 ppt (Maclean, 1974). The “excellent condition attained” by the mangrove oysters (C. echinata) during this study suggests adequate primary productivity for mussel farming.

Figure 3

Figure 3. Map of Milne Bay area, PNG.

Figure 4

Figure 4. Map of Port Moresby Harbour, including Fairfax Harbour, PNG.

Several reservations exist with respect to the potential of the Idumava Point site for commercial mussel farming. Firstly, its proximity to a village of about 1500 residents on Tatana Island, which probably discharges its sewage directly into the harbour, is cause for concern. Monitoring of the sanitary quality of the growing waters and/or the public health quality of the shellfish would be necessary, particularly if export of the mussels is contemplated.

Secondly, the status of the traditional land and fishing rights in the area needs to be clarified, to ensure that legal and social issues will not constrain the development of commercial mussel farming. Ownership issues were one of the possible causes of the failure of the pearl culture (K. La'a, pers. comm.). Other contributing factors may have been economics (Uwate et al., 1984), high mortality (Lock, 1982) and oil pollution (Kan, 1979).

Thirdly, and perhaps most importantly, Port Moresby harbour has a history of red tide outbreaks (Maclean, 1973, 1977) and at least one documented case of paralytic shellfish poisoning, traced to consumption of Crassostrea echinata taken from within the harbour (Worth et al., 1975). Maclean (1974) saw red tides (caused by Pyrodinium bahamense) as “the only constraint to (the development of) an oyster industry”. Red tides could be equally constraining on mussel farming, by requiring either a ban on harvesting mussels during and after the red tide season, or the siting of mussel farms in areas not subject to red tides. Lassul Bay Area, East New Britain

Two sites currently being used for experimental mangrove oyster cultivation were visited. The coastline west of Rabaul is mostly too open and exposed for suspended cultivation of bivalves. The clear oceanic water, allowing extensive coral growth, indicates insufficient primary productivity for intensive shellfish aquaculture. The embayments chosen as oyster farming sites are remote, and within them the areas of higher productivity water are limited to the heads of the bays in close proximity to the mangrove fringe. Relatively slow growth of the mangrove oysters on the experimental rafts, lack of any spat catch over the 2 years the experiment has been running, and the paucity of wild shellfish along the mangrove shoreline, together suggest these sites have very limited potential for intensive suspended culture of either oysters or mussels.

3.2.3 Potential for Green Mussels in PNG

PNG has extensive areas of sheltered coastal water hydrologically suitable for suspended cultivation of mussels. Two of the three areas surveyed, Fairfax Harbour in Port Moresby and Sariba Island in Milne Bay, have sufficient area for large numbers of mussel rafts. In the absence of data on primary productivity the carrying capacity of these areas cannot be determined. However, the successful farming of pearl oysters on rafts in Fairfax Harbour indicates sufficient food is available for intensive cultivation of filter feeding shellfish. Experimental trials would be necessary to determine whether the food availability, on a year round basis, is sufficient for green mussel farming. Numerous similar sites probably exist around PNG's extensive mangrove-fringed coastline.

There was little evidence during these surveys that there are areas suitable for the stake method of mussel culture. For this method, well sheltered highly productive shallow (< 10 m) water is required, overlying a muddy or sandy substrate which is sufficiently firm to support bamboo stakes driven into it.

3.2.4 Alternatives to Green Mussels

Several of the sedentary resource species have potential for aquaculture.

Husbandry of giant clams (Tridacna spp., Hippopus spp.) is a tradition in parts of PNG (Maclean, 1978) and is currently being used to conserve stocks following the ban on the export of these “endangered” species (Keni pers. comm.). Work at the University of Papua New Guinea has indicated the suitability of T. gigas for aquaculture (Lock, 1982). Giant clams are biologically more suited to the extensive reef flats and clear oceanic waters which comprise much of the PNG coastal zone.

Edible oysters (Crassostrea spp) have been the subject of numerous farming experiments in various parts of PNG (Uwate et al., 1984) but none have led to commercial production (Lock, 1982) and the introduction of Crassostrea gigas has been suggested for trial (Maclean, 1974). The successful spat catching achieved during some of these experiments should provide the basis for development of oyster farming sites carefully selected on economic and logistic, as well as biological and environmental criteria.

Pearl oyster (Pinctada spp) farming enjoyed a measure of success before failing, probably for financial reasons. Pearl farming produces a non-perishable high value product, which has advantages over a highly perishable edible end product, particularly for village-based artisanal farming operations in remote and isolated parts of the PNG coastline. The fact that “a potential broodstock of 100,000 adult goldlip oysters at the pearl farm in Fairfax Harbour produced no recognisable spat” (Maclean, quoted in Uwate et al., 1984), may warn of the difficulties of establishing natural spatfalls from introduced species.

Trochus and green snail (Turbo marmoratus) also have non-perishable end products and an enhancement/husbandry style of farming for these species on reefs under traditional fishing rights would be compatible with the coastal village lifestyle.

Seaweed, particularly Eucheuma spp (Johnstone, 1976), and sponge are also potential candidates for aquaculture in PNG, for the same reasons as put forward for the other sedentary resources.

3.3 The Solomon Islands (SI)

3.3.1 Background

The Solomon Islands comprise almost 1000 islands spread over some 800,000 sq. km of sea. The population density, at less than 10 per, is the lowest in the Pacific (total population in 1987 was 286,000) but is growing at over 3% per annum. Most of the population live in a rural subsistence economy.

The country's cash economy is heavily dependent on overseas aid but since the establishment of a locally based tuna fishery in 1971, fishing has developed into the major export industry.

Total exports of marine products in 1988 (37,842 mt) were valued at S$ 84.6 million of which only 1.7% by weight and 7.3% by value were “non-fish” products. These included beche-de-mer, Trochus, green snail, pearl oyster, turtle shell and crocodile skin; with Trochus contributing 70% by weight and 61% by value (unpublished Fisheries Division data).

The SI Fisheries Sector Development Programme for 1985 to 1990 (FFA et al. 1988) included in its objectives “the development of both extensive and intensive systems of aquaculture and mariculture were technically and economically viable” including “the initiation and encouragement of aquacultural projects to produce prawns, seaweeds, clams and other products for local and export markets”, as well as investigation of “the basic environmental conditions and basic biological information regarding the success of aquaculture”.

There has been only small scale aquaculture activity in SI involving crocodiles, mangrove and pearl oysters, prawns, tilapia, turtles and giant clams. Gillett's (1987) SI Fisheries Bibliography lists only 8 references on aquaculture, plus one mangrove oyster study and one on clam harvesting.

A 1979 review of aquaculture potential (Swift and Wickins, 1979) recorded no existing aquaculture and no serious nutritional deficiencies needing the introduction of fish as a protein-source, but suggested that “aquaculture could potentially be used to produce a valuable cash crop to the village communities, cash input being an obvious need for the local economies”. However, “this type of aquaculture would have to be concentrated on … high-priced luxury products such as oysters or mussels”. The report concluded that “the economic viability (of industrial scale aquaculture) of production for the export market is in serious doubt”.

Aquaculture in SI currently comprises one private commercial Macrobrachium farm on Guadalcanal, one government experimental Eucheuma farm (almost ready to go commercial) in Western Province, a few tilapia and crocodile ponds, and ICLARM's clam cultivation activities at the Coastal Aquaculture Centre near Honiara.

3.3.2 Site Surveys

Following discussion with Fisheries Division staff in Honiara, Marau Sound was suggested as the only potential mussel farming site on Efate. Transport was not available for a first hand site survey. Instead the seaweed farming experiments on New Georgia Island, Western Province were visited (Figure 5). This also provided opportunities for inspection of the coastal lagoon type of environmental conditions in the Roviana and Vonavona Lagoons. Both have extensive areas of sheltered, shallow water interspersed with islands and coral reef flats. The dense mangrove areas fringing much of the lagoon probably contribute to the green turbid quality of the water. This apparent high primary productivity indicates good potential for suspended culture of filter feeding bivalves. A brief visit was also made to the Coastal Aquaculture Centre (CAC) just outside Honiara where, since 1986 ICLARM has been undertaking scientific research on hatchery and nursery systems for giant clams, T. derasa and Hippopus hippopus but especially on Tridacna gigas. Low technology raceway systems are used for larval and juvenile rearing and considerable emphasis placed on experimental “grow out” at sites throughout the Solomons. ICLARM has considerable expertise in hatchery and rearing techniques, together with facilities for handling and holding shellfish. The CAC seawater system operates as a straight flow-through with no filtration and no storage.

3.3.3 Potential for Green Mussels in SI

The Solomons Islands have areas of sheltered coastal waters with high primary productivity from mangrove-associated nutrient enrichment. Such areas are probably extensive throughout the multitude of islands in SI, but are limited in Efate, which has the only population centre likely to provide a market for farmed mussels. Sedentary resources are typically not yet over-exploited. Complex national and provincial bureaucratic systems and confused land and seabed ownership issues would hinder the development of commercial mussel farming. Subsistence cropping of green mussel populations established from introductions of seed could provide diversification in food supplies for local coastal communities. Other species for which there are already some aquaculture expertise would have better short term potential than the introduction of green mussels.

3.3.4 Alternatives to Green Mussels

The small experimental Eucheuma farm, situated on a huge expanse of coral flat within the barrier reef at the northern end of the Vonavona Lagoon, has established the potential for farming this seaweed. The seaweed is grown on short lengths of polypropylene string attached to monofilament nylon which is strung between wires held by metal stakes firmly hammered into the coral substrate. Growth from 200 g to the harvest size of 2 kg takes 10 weeks. Farming seaweed is labour intensive, low technology and compatible with village life styles and with traditional reef ownership rights. Each farm can produce its own “seed” stock and the end product is easily handled and non-perishable. Following a survey of potential Eucheuma farming areas, Why (1985) similarly concluded that “income generating activity of seaweed farming would appear compatible with the fishing and gardening activities widely practised by Solomon Islanders”.

Figure 5

Figure 5. Map of New Georgia Island, SI

Giant clam (Tridacna gigas) research at CAC has progressed to the stage of village-operated nurseries in which hatchery reared juveniles are provided for trial cultivation in ocean nursery cages at sites throughout the Solomon Islands (ICLARM, 1989). CAC is also investigating the use of intertidal ponds for ongrowing. The confirmation of giant clam farming as an economically viable operation would provide a boost to other aquaculture activities in the region.

3.4 Vanuatu

3.4.1 Background

Vanuatu's population of under 150,000 mainly live in coastal villages on about 15 of its 80 islands. Much of the rurally based economy operates at a subsistence level. Fishing, within the nations 450,000 sq. km EEZ, is under-developed. Total marine product exports, mostly green snail shell, were valued at only 12 million vatu in 1986 (although re-export of frozen tuna was worth 419 million vatu) compared to imports, mostly canned and processed fish, of 270 million vatu (Fisheries Department, 1987).

The Fisheries Development Plan for 1987–92 (FFA et al., 1988) noted that the resource of inshore reefs and lagoons (448 sq. km) and mangroves (25 sq. km) is small but supplies around 2400 mt of fish and shellfish, mostly for subsistence.

Aquaculture was not specifically addressed in the first part of the Development Plan (DPI) although it was included in DP2 in the context of “pilot trials to test the feasibility of the artificial culture of aquatic organisms and the reseeding of over exploited areas of reef” (FFA et al., 1988).

Aquaculture figures prominently in the “Review of possible research activities with regard to fisheries in Vanuatu” (Grandperrin and Schaan, 1987), in which it was suggested that trials should be aimed at “over-exploited species which are considered as luxury articles either in their natural state or as a processed product”. Trochus, green snail, coconut crab, giant clam, Macrobrachium rosenbergii and possibly green mussel as a new introduction were identified as potential aquaculture species. A research centre was also proposed with the two objectives of mariculture and technology transfer.

Aquaculture activity in Vanuatu has mainly involved edible oysters, with some interest in prawns, rabbit fish and tilapia (Uwate et al., 1984). The Vanuatu Fisheries Bibliography (Gillett and Kenneth, 1987) includes 36 aquaculture references, 22 of which are concerned with oyster culture. Oyster culture was undertaken during the 1970's by a private enterprise, using imported Crassostrea gigas spat. Overseas aid projects in aquaculture have included experimental rearing of Trochus niloticus for reseeding and larval rearing (along with life history studies) of the coconut crab Birgus latro.

There is currently no aquaculture activity in Vanuatu, although the Fisheries Department does have an aquaculture officer with practical experience in New Zealand mussel farming techniques.

3.4.2 Site Surveys

The Erakor and Eratap lagoons were the only sites close to Port Vila considered by Fisheries Department staff to have mussel aquaculture potential. Erakor Lagoon (Figure 6)

The Erakor Lagoon is made up of two basins separated by a narrow and shallow channel. The lagoon has been investigated in recent years and various physical and environmental measurements were recorded (Yuen, 1980; Nerland, 1985; Naidu and Morrison, 1988). Site surveys of both the upper (Emten) and lower (Ekasuvat) basins confirmed some of these published data and observations, with respect to mussel aquaculture potential. Nerland (1985) estimated the surface area and average depth of each of the basins; Ekasuvat 178 ha, 10.7 m; Emten 219 ha, 6.4 m. Depth soundings using a weighted line during our surveys indicated that a large proportion of each basin was extremely shallow (less than 5 m), with perhaps only 35% of Ekasuvat having 5 to 12 m depth and perhaps only 25% of Emten (towards its northern shore) having 5 to 10 m depth.

A “high nutrient level in the lagoon water”, recorded by Nerland (1985), was also indicated during this survey. The water in the Emten basin had a noticeably green and turbid quality and was very still. Ekasuvat basin had much greater clarity and more water movement. Naidu and Morrison (1988) also cited the “nutrient rich water” as a factor contributing to the visible red tide in the lagoon. The apparent abundance of fish and shellfish (local fishermen, pers. comm.), and the evident abundance of starfish and holothurians seen in the shallows, were further indications of the high productivity of the lagoon.

The narrow southern entrance to the lagoon and the presence of coral reefs both in the entrance and immediately outside, must restrict the flow of water into the lagoon. Water exchange between the upper and lower basins is further restricted by the narrow connection between the tow. This is apparent in the average current measurements for the entrance channels and the residence times of water in the two basins as recorded by Nerland (1985) -Ekasuvat 0.4 to 0.7 m per sec., 19 days; Emten 0.1 to 0.5 m per sec., 91 days. Water movement in the parts of the basins with deeper water would be significantly lower than in the entrance channels.

The western shoreline of Ekasuvat basin has extensive residential and hotel development providing numerous potential sources of pollution. Emten basin is less developed with a few houses, a restaurant and a riding school. Eratap Lagoon (Figure 6)

This much smaller lagoon (about 25% the size of Ekasuvat) appeared to have similar characteristics to the Erakor Lagoon including a narrow entrance channel, extensive areas of shallow reef flats, and probably limited water movement. It is more sheltered from prevailing winds than the larger lagoon.

3.4.3 Potential for Green Mussels in Vanuatu

The sites surveyed have areas with appropriate water depth for suspended mussel cultivation. The area available in the Eratap Lagoon is very restricted but sufficient for a few longlines or rafts, providing part-time occupation for local landowners as a source of income and/or food. Erakor Lagoon has perhaps 120 ha of 5 to 10 m depth water and therefore potential for numerous longline systems (the typical New Zealand style 8-longline farm occupies only 3 ha). The high primary productivity, as indicated by the colour and turbidity of the water, suggests sufficient food for filter feeding bivalves (and rock oysters were abundant in the Ekasuvat basin).

The water quality of the Erakor Lagoon, however, poses a major constraint on its potential for aquaculture of filter feeding bivalves. The two recent publications (Nerland, 1985; Naidu and Morrison, 1988) both draw attention to pollution related to septic tank seepages in the lagoon. High faecal coliforms (14 to 152 per 100 ml in the water) and elevated levels of dissolved phosphates and nitrates have been reported (Naidu and Morrison, 1988) as well as depressed dissolved oxygen levels (Yuen, 1980). Water quality has probably not improved since these reports (M. Chambers, pers. comm.) and there is the added danger of red tide blooms possibly resulting from localised eutrophication conditions. Cyclones constitute an added potential constraint on suspended culture systems even in the relatively sheltered situation of these lagoons.

Figure 6. Map of Port Vila area, Vanuatu, showing Erakor and Eratap lagoons.

3.4.4 Alternatives to Green Mussels

The Trochus hatchery project achieved successful spawnings but is now in abeyance. Trochus is fully exploited and reseeding/enhancement would benefit this fishery. This project should be reactivated in the light of recent progress in other countries in Trochus and green snail rearing studies.

The other non-perishable end product species such as green snail, mother-of-pearl, seaweed and sponge are more appropriate aquaculture candidates than the food species.

Mangrove oyster and the local mussel species (Brachidontes sp. and Modiolus sp) could be used to assess intensive farming techniques, in preference to introducing a new species in the form of the tropical green mussel.

Giant clam rearing and outplanting expertise from other tropical countries could be utilised in Vanuatu.

Small local markets, traditional fishing rights and infrastructure difficulties are impediments to any technologically sophisticated marine farming activity in Vanuatu.

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