Most, if not all, marine resources like gastropods are indiscriminately harvested and over-exploited around the world. They are used for subsistence reasons and commercially for industrial purposes. For example, gastropods are utilized as food: they are a good source of protein and protein-rich products. They are usually served as soup in many Japanese, Korean and Chinese restaurants. For industrial purposes such as shell craft production, gastropod shells are made into lampshades and fashion accessories like buttons, and the mother of pearl flakes from powdered scrap resulting from the button manufacture have found many applications in the formulation of lacquers and shampoo (Nash, 1981). Clearly, to continue such widespread use, it is important that this resource be utilized in a sustainable manner to ensure its presence for future generations.
Green snail, Turbo marmoratus, belongs to the family Turbinidae. It is the largest herbivorous gastropod and inhabits the shallow coral reef region. The measured shell height may exceed 20 cm, and its body weight may reach over 3 kg. Its natural area of distribution ranges from Western Indian Ocean localities like Kenya, Tanzania, and the Seychelles, to the Western Pacific and Southeast Asian countries like Vanuatu, Solomon Islands, Papua New Guinea, Indonesia, Malaysia, Philippines, and upward to the Ryukyus. (Yamaguchi, 1988).
Green snails, because of their highly valuable nacreous shell, have been exploited extensively for inlay and many handicrafts. Their meat provides a rich source of protein and is used both in exotic seafood dishes and as a food source used by local people. Because of its great value the species has been extensively over-fished, and is now rare or extinct in many areas where it was once abundant.
Until recently very little research had been done on this species. The first trial of green snail seed production was carried out successfully by Dr. Yamaguchi, University of Ryukyu, in 1988. The Japanese have pioneered the study of green snail seed production at two fish farming centers: Okinawa Prefectural Fisheries Research Laboratory, Yaeyama branch located in Ishigaki Island, and Kagoshima Prefectural Fish Farming Center located in Kagoshima. Successful mass seed production of green snails has been undertaken at the Okinawa Prefectural Sea Farming Center since 1989 (Murakoshi, et al., 1993), and seed releases for sustenance of the green snail resources have been carried out in some parts of the Ryukyu archipelago within the last ten years.
Transplantation of green snails around the Pacific region has been very limited. The only successful transplantation recorded was carried out in the French Polynesia area in 1966, using green snails imported from Vanuatu (Yen, 1991). Another transplantation attempt was made in New Caledonia with green snails from Vanuatu; however this transplantation was either unsuccessful or the results are unknown (Yamaguchi and Kikutani, 1989).
In August 1993, a total of 50 green snails were introduced to Tonga from Vanuatu (Fa'anunu and Sone, 1994). Twenty were released at Vaini and 21 were released at 'Euaiki Island. Nine died before release. The following year, 320 snails were transported from Japan to Tonga (Fa'anunu and Kikutani, 1995). Successful seed production and rearing methods in Tonga have resulted in some snails being released in suitable sites around Tongatapu Island and Vava'u Islands.
One of the heavily exploited gastropod resources for the last decade is the top shell, Trochus niloticus. It has been harvested in large quantities particularly, in South Pacific area. Due to the many uses of this marine animal, the demand for it has increased considerably in the last two decades, which has resulted in over harvesting. As a consequence, the natural population of the top shell T. niloticus is dwindling and is dangerously near extinction. It is now imperative to draw up appropriate conservation measures and management schemes in order to sustain the remaining natural stock of the topshell T. niloticus.
To sustain the availability of the trochus supply, management strategies must be formulated and implemented. Prior to this, basic information on their ecology and reproduction biology etc. must be generated to form the basis of such schemes. These techniques could be used later to enhance the population growth of Trochus niloticus. (The transplantation process of trochus is described in Subsection 2.2.2)
Abalones, which belong to the Haliotis family, are the most valuable marine gastropods from an Epicurean point of view. When mention is made of edible gastropods, one usually think first of the land snail so esteemed by French gourmets. Abalone is a herbivorous marine gastropod that inhabits coastal reef zones.
There are approximately 75 species recorded in the world, and about 20 of these species are relatively large in size, and are highly valuable. They are generally captured by commercial fishery. Important abalone fisheries exist only in Japan, Australia, New Zealand, Mexico and the coast of United States.
In the tropical areas three important species have been reported, namely the Haliotis asinina, H. ovina, and H. diversicolor. Abalones are slow moving inhabitants of rocky intertidal areas and are easy prey for people fishing. Because of this, their numbers have declined in all the countries mentioned. It is somewhat surprising, considering the scarcity of abalone and the high price they command, that abalone culture has been undertaken only in Japan, California and Taiwan.
They are relatively small compared to the commercial species traded on the international market. Presently there is no commercial fishery for them in the Pacific Islands since the wild stocks are not a familiar food item for the Pacific people. However, when their large-scale production becomes possible, a potential demand for these species may be created in both domestic and international markets. This has been the case with the small-size abalone species H. diversicolor, which is highly appreciated in Asian countries like Japan, China and Korea (Singhagraiwan and Doi, 1993).