PACIFIC OYSTER INDUSTRY IN HONG KONG
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Bromhall (1958) reported upon an experiment using raft culture (*) in Deep Bay and showed that the oysters reached marketable size in two and a half years instead of four. Furukawa (1968) in a review of Japanese oyster culture reports that the raft method of culture has now virtually replaced all other methods of shellfish culture in that country, and that by this method the annual production of oysters has increased enormously, for example in Hiroshima. According to Quayle (1969) in his study of Pacific oyster culture in British Columbia, this method of culture is the most efficient with regard to the intensity of spatfalls and the subsequent growth and survival of the oyster. By this method, the culture of oyster is no longer limited to the shore and can be extended to deeper waters, thereby increasing the area available for culture. Recently conducted experiments undertaken by the Agricultural and Fisheries Department of the Hong Kong Government designed to test the feasibility of extending the oyster industry to the north side of Lantao Island (*) (Fig. 1) have been successful (Mok, 1974). The oysters are able to breed naturally in these waters and the reported growth rate is even faster; the oysters requiring only two years to reach marketable size. Oysters suspended in the water can utilise the whole column of water thereby reducing intraspecific competition. Moreover bottom living predators cannot attack the suspended oysters. In addition the large number of spat collected by this method can be separated from the cultch after one year and cultivated on trays, thereby solving the problem of overcrowding.
Raft culture involves a similar amount of labour as that used in bottom-laying but the more arduous and unpleasant aspects of the work (i.e. the laying of the cultch on the muddy sea bed) are avoided. The strings of cultch to be suspended from the rafts can be prepared on land beforehand. During harvesting the strings of oysters can be hauled up from the raft into a boat, which is much easier than diving or tonging as is practised in Deep Bay. The advantage to such a system are many and obvious and result in larger spatfalls, a faster rate of growth, better quality of the flesh, reduced mortality and easier management. Since the surface waters of Deep Bay are less polluted (Leung et al., 1975), the oysters too would be safer to eat.
The increased intensity of fouling upon the strings is a problem but has been solved, for Pearl oysters at least (Mawatari and Miyau-
PACIFIC OYSTER INDUSTRY IN HONG KONG
147
Bromhall (1958) reported upon an experiment using raft culture T✰✰✯) in Deep Bay and showed that the oysters reached) marketable size in two and a half years instead of four. Furukawa (1968) in a review of Japanese oyster culture reports that the raft method of culture has now virtually replaced all other methods of shellfish culture in that country, and that by this method the annual production of oysters has increased enormously, for example in Hiroshima. According to Quayle (1969) in his study of Pacific oyster culture in British Columbia, this method of culture is the most efficient with regard to the intensity of spatfalls and the sub- sequent growth and survival of the oyster. By this method, the culture of oyster is no longer limited to the shore and can be ex- tended to deeper waters, thereby increasing the area available for culture. Recently conducted experiments undertaken by the Agri- cultural and Fisheries Department of the Hong Kong Government designed to test the feasibility of extending the oyster industry to the north side of Lantao Island (✯✯ 2) (Fig. 1) have been success- ful (Mok, 1974). The oysters are able to breed naturally in these waters and the reported growth rate is even faster; the oysters requiring only two years to reach marketable size. Oysters suspend- ed in the water can utilise the whole column of water thereby reducing intraspecific competition. Moreover bottom living preda- tors cannot attack the suspended oysters. In addition the large number of spat collected by this method can be separated from the cultch after one year and cultivated on trays, thereby solving the problem of overcrowding,
Raft culture involves a similar amount of labour as that used in bottom-laying but the more arduous and unpleasant aspects of the work (i.e. the laying of the cultch on the muddy sea bed) are avoided. The strings of cultch to be suspended from the rafts can be prepared on land beforehand. During harvesting the strings of oysters can be hauled up from the raft into a boat, which is much easier than diving or tonging as is practised in Deep Bay. The ad- vantage to such a system are many and obvious and result in larger spatfalls, a faster rate of growth, better quality of the flesh, reduced mortality and easier management. Since the surface waters of Deep Bay are less polluted (Leung et al., 1975), the oysters too would be safer to eat.
The increased intensity of fouling upon the strings is a problem but has been solved, for Pearl oysters at least (Mawatari and Miyau-
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