The present location of the trochus hatchery is unsuitable because of the polluted water in Port Vila Bay. It is therefore essential that an alternative site be chosen.
Factors to consider when choosing a new site include the following:
seawater quality;
availability of flat land near the shore on which to place the tanks, pumps and buildings;
ability to lease the land from the owners; and
availability of electricity.
A site remote from industrial and urban effluent is essential if a high-quality seawater supply is to be assured. Water movement (tides or currents) should be sufficient to exchange rapidly the water around the intake line. The site should therefore be a relatively exposed one, and should not be enclosed by islands the way the present one in Port Vila is (Fig. 1).
The shoreline adjacent the site should drop off rapidly, not be gently shelving. There are two reasons for this: firstly, the intake line need not extend far into the sea to reach good quality water or be below the level of low water spring (LWS) tides; and secondly, sediment levels are less in places with a narrow intertidal area. The shorter the intake line, the less strain on the pumps, and the smaller the reduction in flow rates caused by frictional drag in the line.
An old Macrobrachium (freshwater shrimp) farm near Mélé, near Port Vila was examined as a possible alternative site. This farm is no longer operational. The first two of the above criteria are satisfied by this site. Since this land was leased previously for Macrobrachium culture, it seems likely that it would be available for trochus culture, although this would need to be confirmed.
There are also some large circular concrete tanks in place, as well as concrete buildings. The tanks appear to be useable without a great deal of maintenance.
A disadvantage of this site is the lack of an electricity supply; installation of an electrical generator would be necessary. Unless it were possible to employ a competent mechanical engineer or diesel engine mechanic to service the generator, an alternative site supplied with electricity from the national power grid would be preferred.
Other possible sites, such as on the island of Espiritu Santo, were not examined because of lack of time. However, it is recommended that sites on Espiritu Santo be examined for their suitability.
Trochus culture in Vanuatu will have a greater chance of success if it is adopted after the basic problems listed in Section 3 (particularly survival rates after outplanting) have been solved in a place where the necessary infrastructure (trained personnel and an established aquarium facility) already exists.
Substantial progress in trochus culture has been made in Okinawa, Japan (M. Yamaguchi, personal communication, January 1989). Significant advances have also been made at the Micronesian Mariculture Demonstration Center (MMDC) in Palau (Heslinga 1981; Heslinga and Hillmann 1981).
It is recommended that the aquaculturist appointed to run the Vanuatu hatchery undergo training in the techniques of trochus culture and ranching in Okinawa. Modification of these techniques may then be made, if necessary, to suit Vanuatu conditions. Details of hatchery design may also be learned there, as well as at the MMDC in Palau.
Ranching of trochus cannot seriously be considered as a tool for managing the wild fishery until it has been shown that it is an effective means of enhancing the wild stocks. Management of the wild fishery must therefore be based on sound conservation practices, such as strict adherence to appropriate size limit regulations, and perhaps restrictions on the total annual catch. There is the danger that re-seeding will be used as an excuse to harvest the wild stocks without regard for conservation. This must not be allowed to happen.
It is useful to review briefly the effectiveness of ranching to enhance natural stocks of sedentary but mobile species, as well as its economic feasibility. Only abalone (Haliotis species) is considered here, because of its developmental and ecological similarities with trochus, and because of the major advances that have been made in this area with this animal.
Most advances in abalone ranching have been made in the United States and, especially, Japan, where a great deal of effort is put into ensuring high survival rates in the sea after outplanting. Selected invertebrates (starfish, octopus and urchins) are harvested prior to the planting of abalone seed to reduce losses from predation and competition (Kan-no 1975). Temporary transplantation cages are also used to reduce early mortality from predation, and to allow acclimation of the outplanted seed to the natural benthic environment (Saito 1979, 1981; Miyamoto et al. 1982). The Japanese re-seeding programmes are heavily subsidized by the government, and are yet to be proven profitable. Yamaguchi (1988) has also discussed the application of protective shelters for ranching of tropical marine benthic animals.
In the United States, the Japanese method of cage protection of outplanted juvenile abalone has also been tested for enhancing survival rates (Ebert and Ebert 1986, 1988). Again, the economic viability of this is still to be demonstrated (Hooker and Morse 1985). Attention is being given increasingly to the outplanting of very small juvenile abalone (Hooker and Morse 1985) because, although mortality rates of these are higher, the much greater numbers that can be outplanted, coupled with the much lower cost of producing smaller seed, suggests that this approach may be more cost effective.
Some effort should be made to consider, and hopefully avoid, the conflicts between villages which may arise as a result of property rights to parts of the fishing grounds or reef being held by individuals, families or clans. These rights exist in many Pacific island cultures (Johannes 1988), and have been the cause of a number of disputes when fish were taken for cash rather than subsistence.
The risk of territorial disputes occurring over trochus is real: Johannes (1988) quotes a witness in Papua New Guinea court case: “Before in customary times we had no trouble… But when trochus became a business the disputes over the controllers of the reef started”.
These problems apply to aquaculture as much as to fishing. Johnston (1977; cited in Johannes 1988) raised the question of the relationship between aquaculture and property rights. Johannes extended Johnston's theorizing to the arena of the Pacific islands: “One can…imagine [conflicts] within a subdivided [reef tenure system] where one clan or family happens to own the fishing rights to the best location for an aquaculture development”.
This scenario may readily be applied to trochus ranching when the reef area owned by one village may be better suited to ranching than areas owned by other villages - for example, because of greater area of juvenile habitat.
There is the risk that this may contribute to the breakdown of the traditional reef tenure system. Johannes (1988) has argued that the traditional reef tenure system, when linked to a traditional reef conservation ethic, may greatly assist in the management of easily-depleted resources.
