Over 450 pages of text were required to publish a comprehensive review of aquaculture activities in Pacific Islands up to 1983 (Uwate et al., 1984). The large size of the review is indicative of the wide variety of species and the diversity of environmental situations that have been the focus of aquaculture activity in this region. Much of this activity was instigated by the positive recommendations as a result of general assessments of aquaculture potential throughout the Pacific (Glude, 1971, 1972, 1982; Villaluz, 1972; Doumenge, 1973; Brewer & Corbin, 1982) as well as from detailed species or site-specific recommendations for individual countries (Uwate et al., 1984).
The 1988 report of a Joint Fisheries Strategy Mission which looked at opportunities for fisheries development in the South Pacific suggested that the increasing attention being paid to aquaculture programmes in the region was so because “island governments see aquaculture as a means of generating cash income at the village level and as an alternative to the capture fisheries, particularly in those areas where the lagoon resources are overfished” (FFA et al., 1988). The report, however, cautioned that “despite the large number of active and planned projects in the region, few are economically viable at present and it is unlikely that many will develop beyond the experimental stage”.
The green mussel (Perna spp.) has frequently been identified as a potential organism for aquaculture in the Pacific Islands (Uwate et al., 1984). The governments of the Federated States of Micronesia, Papua New Guinea, the Solomon Islands and Vanuatu requested assistance from FAO's South Pacific Aquaculture Development Project in assessing each country's potential for the development of green mussel farming. As a result, during March and April 1989, Mr R. W. Hickman, a fisheries scientist in the Aquaculture Section of the New Zealand Ministry of Agriculture and Fisheries, with over 15 years involvement in mussel farming in New Zealand, visited the four Pacific nations to make the assessment.
The general terms of reference provided by FAO for this consultancy were:
To make a preliminary feasibility study of green mussel farming by site assessment in the Federated States of Micronesia, Papua New Guinea, Solomon Islands and Vanuatu;
to advise on appropriate farming techniques, further requirements and subsequent steps needed to begin mussel farming;
to produce a study report.
Specific terms of reference prepared by the Governments of Papua New Guinea (PNG) and the Solomon Islands (SI) were:
PNG: - to visit the Port Moresby headquarters of the Department of Fisheries and Marine Resources and discuss the biological, environmental and economic implications of green mussel farming in Papua New Guinea, particularly in the Milne Bay Province;
- to make field visits to sites designated by the Department and collect information pertaining to the feasibility study;
- to produce a report detailing activities and findings at the end of the visit.
SI: - to meet with officials of the Fisheries Division, Ministry of Natural Resources and discuss in broad terms the possibilities for the development of green mussel farming in the Solomon Islands, considering potential sources of seed and grow-out areas, appropriate culture techniques, harvesting matters and markets;
- to meet with staff of SIG/ICLARM Coastal Aquaculture Centre and appraise possibilities of mussel farming fitting it in with the overall work programme of the Center;
- to travel if necessary to a couple of potential sites for mussel farming within the country and hold discussions with appropriate provincial authorities;
- to produce a brief report for Fisheries Division on the results of the visit, with particular reference to the viability of pursuing the matter further.
The Federated States of Micronesia requested the feasibility study for the states of Pohnpei and Kosrae only. Vanuatu did not prepare specific terms of reference but “the Second Lagoon near Port Vila” was identified for study.
The visits to Micronesia took place on the 5th to 13th March 1989, and to Papua New Guinea, the Solomon Islands and Vanuatu on the 29th March to 22nd April 1989. A detailed schedule of travel (Appendix I) and persons consulted (Appendix II) during the study are included in this report, which was prepared for submission to Mr Hideyuki Tanaka, Regional Aquaculturist, South Pacific Aquaculture Development Project, Suva.
Mussels are farmed extensively throughout the world. Four countries; Spain, China, Denmark and Holland each have an annual production of about 100,000 mt with Spain and China using suspended cultivation techniques and Denmark and Holland using seabed cultivation. However, the vast majority of the world's annual production of 800,000 mt comes from the farming of blue mussels Mytilus edulis and M. galloprovincialis with only 10% being derived from the green mussels Perna viridis (= Mytilus smaragdinus) and P. canaliculus (FAO, 1988a).
The two green mussel-species have separate distributions. Perna canaliculus is restricted to the temperate waters around New Zealand, whereas P. viridis occurs widely in tropical waters throughout the Indo-Pacific region from the Persian Gulf to southern Japan and through Malaysia, Indonesia and the Philippines (Siddall, 1980). A closely related brown mussel Perna perna is found around the African continent and in the northern half of South America.
Green mussels are farmed commercially in Thailand, the Philippines and New Zealand. India has a mussel fishery based on wild stocks of green mussels. Subsistence cropping of green mussels is common in those countries where they occur naturally. New Zealand is the only country that exports significant quantities of green mussels (FAO, 1988b).
The green mussel is not endemic in the tropical islands of the Pacific. It has been introduced to several countries, at various times, specifically for aquaculture purposes. Perna viridis from the Philippines was first introduced into New Caledonia in 1972 and Fiji in 1975, as well as into Tonga in 1978 (following a 1976 introduction from Malaysia). Mussels were transferred from New Caledonia to French Polynesia in 1978 for the development of larval rearing techniques (Uwate et al., 1984). The AQUACOP hatchery in Tahiti subsequently provided Perna viridis seed for mussel farming trials in Fiji and Samoa as well as in French Polynesia.
All these attempts at farming have produced small crops of mussels but as noted by Waugh (1986) “the benefits of (the) projects have rarely been sufficient to make them commercially viable”. Recent assessments of the potential for green mussel farming in both Fiji (Hickman, 1987) and Western Samoa (Tanaka et al., 1988) have cast doubt on its economic viability.
Waugh (1986) listed a number of factors which have contributed to the very limited success of aquaculture in the South Pacific. The factors include the small size of the island populations, their isolation from the larger markets, poor transport and communication systems, and lack of infrastructure and refrigeration facilities, but “most importantly, the cultural and social characteristics of the islanders, and their traditional background have not proved conductive to aquaculture development in general”.
It has been assumed throughout this study that any mussel farming development in these four Pacific nations would be based on introductions of the tropical green mussel Perna viridis, since the temperate species P. canaliculus is unlikely to tolerate the high water temperatures in these tropical regions.
Several aspects of the biology, ecology and culture of green mussels which were recently and comprehensively reviewed (Vakily, in press) are pertinent for any assessment of mussel farming in the Pacific Islands and provide criteria for evaluating its potential.
The tropical green mussel Perna viridis occurs typically in estuarine or coastal waters that are rich in plankton, warm (26 to 32 degrees Celsius) and of high salinity (27 to 33 ppt). Mussels can tolerate short periods of exposure to extreme temperatures and salinity, and to high turbidity of suspended sediments.
Mussels require a firm substrate for larval settlement and for subsequent byssal attachment throughout their juvenile and adult life. The current flow of water must be adequate to provide sufficient food for growth, to prevent build up of faecal and pseudofaecal material, and to disperse the larvae during their 3 to 4 weeks free-swimming phase.
Mussels are subject to predation by starfish, crustaceans and fish throughout their whole life. It is possible too that carnivorous molluscs and annelids predate on spat and juveniles. Few parasites and diseases of green mussels are yet to be reported.
Mussels are filter feeders feeding predominantly on phytoplankton and occasionally on detrital suspended matter. High levels of inorganic suspended matter reduce the mussel's feeding ability by “diluting” the amount of nutritionally useful material that it is able to filter. As filter feeders, mussels are vulnerable to organic and chemical pollution and to natural phytoplankton blooms such as red tides.
There are essentially three methods of farming green mussels:
On-bottom culture:
This requires either a firm seabed area on which the juvenile mussels themselves can be laid to grow to harvestable size (following collection from another site where over-abundant settlement has occurred), or a suitable material like mussel or oyster shells can be spread to provide settlement surface for catching the mussel spat in situ. This system of culture, however, leaves the mussels exposed to their major predators, starfish and crabs, and vulnerable to siltation.
Stick (or stake) culture:
This is used to raise the mussels off the bottom. Lengths of bamboo or mangrove are staked into the seabed, typically muddy sand, in an area where a natural settlement of mussels can be obtained. Various arrangements of stakes, single or connected, can be used for different degrees of exposure or water movement. Stick culture produces faster growth and lower mortality than on-bottom culture.
Suspended culture:
This uses rafts or floats to support ropes on which the mussel settlement occurs, and growth to harvestable size takes place. Suspended culture can also be achieved by hanging the culture ropes from horizontal frames supported by posts set into the seabed. Suspended culture provides much greater control over predation and mussel density as well as optimising feeding conditions.
In all methods of culture, mussels are grown in high density and adequate food supply is a critical factor. The amount of food available to the mussels is dependent on the standing stock of phytoplankton, the rate of primary production and the rate of replenishment of the nutrients or phytoplankton by water flow into the mussel culture area. Plankton concentrations of 104 cells per ml (AQUACOP and de Gaillande, 1979) or 17 to 40 micrograms of chlorophyll al (Cheong, 1982), net primary production of 27 to 100 micrograms of carbon per cubic meter per hr (Glude, 1984) and currents of 0.2 to 0.4 m per sec (Cheong, 1982) have been suggested as suitable for the culture of Perna viridis.
The three culture methods require differing degrees of expertise and capital investment but all require a reliable supply of spat to initiate and maintain mussel farming. Commercial mussel farming relies on natural spat catching, which in turn is dependent on the reproductive capacity of wild mussel populations. Hatchery spat production of Perna viridis (Coeroli et al., 1984) has provided seed stock only for experimental farming in areas lacking natural populations.
Evaluation of mussel farming potential involves biological, environmental and socio-economic criteria as well as an assessment of realistic alternative species and aquaculture developments.
For green mussel farming, where actual farming techniques are well established, availability of spat or seed, mortality and/or predation throughout the growth period, and quality or condition of the harvestable product are the principal biological criteria.
High primary productivity in coastal waters sheltered from oceanic waves and tropical storms are environmental requirements.
Socio-economic criteria include tenure, security and traditional fishing rights to the potential farming areas, as well as the marketing opportunities and constraints for both domestic and export outlets. Labour and equipment costs are fundamental to the economic viability of the various farming methods. Infrastructure aspects such as transport, freezing and processing capacity, together with government support by way of policy, advisory services and financial assistance are fundamental to the development of an industry.
Tradition and culture need to be considered in the evaluation of green mussel as opposed to alternative species, as does the role of a new protein food source in the diet, in subsistence or cash-cropping, or in the economy at local, national or international levels.
