For mussel farming to be biologically feasible, four basic criteria must be met:
a reliable source of spat must be available;
phytoplankton production must be sufficient to sustain rapid growth of mussels in high densities
mortality from disease and predation must be low;
the mussel meat must be of high quality and free from pollution.
Numerous socio-economic factors; covering site tenure and security, labour and equipment costs, market capacity, essential support and infrastructure facilities and others, will affect the viability of mussel farming, even when the biological criteria are satisfied.
Spat:
The tropical green mussel Perna viridis is not endemic to Micronesia, Papua New Guinea, the Solomon Islands or Vanuatu. The supply of spat for green mussel farming in these countries therefore involves the introduction of a new species. Some of the risks inherent to such an introduction can be minimised by importing only hatchery-reared seed. IFREMER in Tahiti is the only source of hatchery seed in the South Pacific region. However, since it is likely that large quantities of seed will need to be imported over several years to successfully establish mussel farming, all the factors discussed in FAO's “Codes of practice and manual of procedures for consideration of introductions and transfers of marine and freshwater organisms” (EIFAC Occasional Publication No. 23), should be analysed for each nation, having particular regard to the ecological impact of green mussels.
Productivity:
Tropical coastal waters typically have low primary productivity. In these Pacific island nations, high productivity occurs only in sheltered embayments in association with mangroves. It is yet to be determined, even in these areas, whether the primary productivity is sufficient, on a continuing basis, to support the high density populations necessary for commercial mussel farming.
Mortality:
Although disease has not been a problem in mussel farming, losses from predation can constitute a serious threat to farming viability. Vulnerability to predation is dependent on the method of farming, whether on-bottom or off-bottom. The mangrove crab, Scylla serrata, is a potential predator throughout the mussel's entire life cycle, while several of the browsing fish species could predate particularly on the seed mussels. Predation is likely to be a site-specific problem.
Quality:
Tropical mussels typically do not attain the high condition found in temperate species. The condition or meat yield of mussels varies seasonally, principally in relation to the reproductive cycle. Tropical mussels tend to spawn irregularly throughout the year. Poor condition after spawning and variation in condition between individuals will lead to quality control problems at harvesting. Sporadic spawning also mitigates against successful catching of wild spat. Mussels are highly susceptible to pollution, and in the high productivity areas most suited to mussel culture in the tropics, red tides and their associated shellfish poisoning constitute a major impediment to shellfish farming.
Socio-economic factors likely to constrain the development of mussel farming in these Pacific island nations include the resolution of traditional custom rights to coastal areas and the influence of such rights on tenure, security and ownership of farm sites, farm equipment and farm production. Mussel farming should be a market-driven activity, to meet defined local or export demand, and based on a production cost structure appropriate to the market capacity and the market value of the end product. This must take into account the cost, availability and expertise of local labour, as well as such marketing aspects as food preferences, transport facilities and processing capabilities, which determine the acceptability of the product in the market place. Proximity of the farming activity to the market is important for a perishable food product such as green mussel, particularly in the high temperatures of the tropics and when storage and transport facilities are limited.
Finally, the potential for green mussel farming in these Pacific nations must be weighed against alternative options for fisheries developments, including the utilization of indigenous mussel species or the development of aquaculture activities using other organisms. Giant clam, seaweed, sponge, Trochus and green snail are more suited to the oceanic coral reef environment that predominates around these islands. Oysters and cockles may be more suited to the turbid conditions and high silt loadings that typify the high productivity of the mangrove-associated coastal waters. Enhancement style husbandry for clam, Trochus or green snail is more in keeping with traditional Pacific coastal lifestyles. Non-perishable end products have distinct advantages if the aquaculture development is directed at generating income and employment opportunities rather than food production.
Green mussels could provide a much needed additional source of fresh protein for local consumption but would have to be grown as a subsistence crop using minimum production-cost methodology. This would necessitate the establishment of self-sustaining populations of green mussels (derived from initial introductions of hatchery-reared seed) to provide a source of spat.
Sites suitable for suspended cultivation for the production of cash crops are available but experimental trials would be required to determine basic data on growth, mortality, predation and meat quality.
Open access to all submerged coastal areas, as found in Pohnpei and Kosrae, should facilitate the setting up of mussel farms, but could preclude security and tenure.
FSM has the expertise within the state fisheries divisions and the Community College to undertake the introduction of green mussels and the monitoring and preliminary trials necessary to define mussel farming parameters.
Seaweed and sponge farming trials and production within FSM, and recent innovations in hatchery techniques for Trochus and green snail elsewhere, show that these species have a much greater potential for generating income than green mussel farming.
Papua New Guinea has extensive areas of coastal water with potential for farming green mussels which are, however, generally remote from the population centers. Experimental trials using imported hatchery-reared seed are needed to confirm the biological suitability of typical areas, but logistics, infrastructure, lack of aquacultural expertise and particularly the red tide hazard are serious constraints.
Clear definition of traditional fishing rights is a necessary pre-requisite to mussel farming development.
The Motupore Island Research Station (of the University of Papua New Guinea) would be an appropriate organization to undertake a green mussel introduction programme, in cooperation with the Fisheries Division.
With large under-exploited coastal fisheries resources, Papua New Guinea has only limited incentive to develop aquaculture, particularly aquaculture based on an introduced species. Clam farming, in which the Motupore Research Station already has some experience, and Trochus or green snail husbandry have greater short term aquaculture potential than green mussel.
The Solomon Islands have in the Solomon Islands Government (SIG)/ICLARM Coastal Aquaculture Centre, a facility and body of scientific expertise appropriate to undertake the introduction of a new species, using imported seed, or even to introduce the technology for hatchery production of green mussel seed, as a regional resource for the western Pacific. However, the Solomon Islands appear to have minimal interest or incentive in developing green mussel farming. Potentially suitable areas exist but they are remote from the principal market, in the capital Honiara, and even this market is small.
Aquaculture promotion efforts would be better directed at commercial realization of the experimentally successful Eucheuma farming and ICLARM's giant clam farming activities.
Vanuatu imports small quantities of New Zealand green mussels principally for the restaurant and hotel market in Port Vila. Mussel farming is seen to have potential for import substitution. The small size of this market (probably less than 10 metric tonnes (mt) per annum) and the dubious sanitary quality of the potential mussel farming areas close to Port Vila, suggest that the development of mussel culture based on this established market would be inadvisable.
Vanuatu has the facilities and scientific expertise to undertake the introduction of tropical green mussels, using hatchery-reared seed, to further diversify the fauna available for subsistence cropping.
Continuation of the Trochus hatchery work for enhancement of this over-exploited resource would have more immediate benefit than attempting to introduce green mussels.
The FAO South Pacific Aquaculture Development Project (SPADP) should facilitate the introduction of green mussels Perna viridis into Micronesia, with the aim of establishing self-sustaining populations.
A two to three year research project should be developed, using overseas scientific expertise, for experimental introductions and monitoring, to be implemented by the national and state fisheries organizations in Pohnpei and Kosrae and the Community College of Micronesia. The development of the project should include a through analysis of the apparent success of establishing natural spatfalls of green mussels in Western Samoa (reported by Tanaka et al., 1988).
The research project should include both on-bottom and off-bottom techniques to provide data for realistic assessment of farming potential.
SPADP should facilitate experiments to determine the biological suitability of the green mussel Perna viridis for farming in Papua New Guinea, by supplying seed and farming expertise to a suitable local organisation such as the Milne Bay Fishing Authority.
The Coastal Aquaculture Centre in the Solomon Islands should be encouraged and supported to develop low technology rearing methods for green mussels Perna viridis.
SPADP should facilitate the introduction of green mussel Perna viridis into Vanuatu by supplying seed to the Fisheries Department for experiments in suspended and bottom culture.
The fisheries organisations in Micronesia, Papua New Guinea, the Solomon Islands and Vanuatu should make firm commitments to the development of their aquaculture potential, primarily for indigenous species, by increasing their aquaculture expertise.
Any development of green mussel farming in these Pacific Island nations should be clearly aimed at domestic consumption, either at a subsistence or a cash-crop economic level.
