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Rafting is a common method of culturing oysters in many parts of the world, but has not yet become popular with Hong Kong farmers, despite the significant reduction in growth periods found in experiments conducted in Deep Bay and off Lantau Island (Bromhall, 1958; Mok, 1974b). There are currently some 200 rafts in Deep Bay off Shekou; 30 are operated by the Nantou oystermen and the remainder by the Shajing based oystermen. Two types of raft are used; one about 84 m2 in area, and the other 110 m2. The rafts are constructed from bamboo and expanded polystyrene floats and three rafts are moored by two anchors. Baskets, made from nylon or polypropylene rope with a 30 mm mesh, are attached to the rafts, such that the oysters are always above the sea bed and covered by about 1 m of water. Each basket holds 40 marketable size oysters, the equivalent of 1 kg of wet weight flesh. The advantages of the rafting system are the reduced growth period (about 21/2 years) and consequently enhanced productivity. Oysters are taken from the traditional cultches at about 11/2 years of age and placed in the baskets for growth and fattening over about a further year. The problem of oyster shells cutting through the basket ropes does not seem to be too serious, but clearly greater capital investment is required in the rafting technique compared to bottom-laying.
Oyster bed productivity
The productivity of an oyster bed is difficult to ascertain in view of the different cultch and spacings adopted, and because access to the beds and visibility is so poor. Mok (1974a) reports in his experiments that the density of 5 year old oysters was 89/m2 with an average of 9.2 oysters per cultch. The average wet weight of the soft parts of a marketable size oyster is about 25 g (Binnie & Partners, 1984). The biomass or standing crop would therefore be about 2.2 kg/m2 and, assuming a five year growth period, the production of oyster flesh would thus be 0.45 kg/m2 year. This production is a net figure, since no allowance is made for non-productive areas of the oyster bed (e.g., access paths).
Hong Kong oyster farmers indicated that 10,000 cultches with a range of marketable size oysters on each cultch of between 5 and 15, would take up an area of about 743 m2. Assuming 10 oysters
175
Rafting is a common method of culturing oysters in many parts of the world, but has not yet become popular with Hong Kong farmers, despite the significant reduction in growth periods found in experiments conducted in Deep Bay and off Lantau Island (Bromhall, 1958; Mok, 1974b). There are currently some 200 rafts in Deep Bay off Shekou; 30 are operated by the Nantou oystermen and the remainder by the Shajing based oystermen. Two types of raft are used; one about 84 m2 in area, and the other 110 m2. The rafts are constructed from bamboo and expanded polystyrene floats and three rafts are moored by two anchors. Baskets, made from nylon or polypropylene rope with a 30 mm mesh, are at- tached to the rafts, such that the oysters are always above the sea bed and covered by about 1 m of water. Each basket holds 40 marketable size oysters, the equivalent of 1 kg of wet weight flesh. The advantages of the rafting system are the reduced growth peri- od (about 21⁄2 years) and consequently enhanced productivity. Oysters are taken from the traditional cultches at about 11⁄2 years of age and placed in the baskets for growth and fattening over about a further year. The problem of oyster shells cutting through the basket ropes does not seem to be too serious, but clearly greater capital investment is required in the rafting technique compared to bottom-laying.
Oyster bed productivity
The productivity of an oyster bed is difficult to ascertain in view of the different cultch and spacings adopted, and because access to the beds and visibility is so poor. Mok (1974a) reports in his experiments that the density of 5 year old oysters was 89/m2 with an average of 9.2 oysters per cultch. The average wet weight of the soft parts of a marketable size oyster is about 25 g (Binnie & Partners, 1984). The biomass or standing crop would therefore be about 2.2 kg/m2 and, assuming a five year growth period, the production of oyster flesh would thus be 0.45 kg/m2 year. This production is a net figure, since no allowance is made for non- productive areas of the oyster bed (eg access paths).
Hong Kong oyster farmers indicated that 10,000 cultches with a range of marketable size oysters on each cultch of between 5 and 15, would take up an area of about 743 m2. Assuming 10 oysters
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