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fattened. Oysters are also placed directly on the sea bed, particularly close to the shore. This practice seems to provide an accessible "store" for marketing purposes.
The choice between tile or post seems to be one of personal preference or perhaps supply so far as Hong Kong oyster farmers are concerned. The posts have about 0.01 m2 available for spat collection compared to 0.02 m2 with the tile. These areas are an average estimated from inspection. The posts do not need to be raised so often as a result of deposited sediment, which may account for their predominance in parts of the Chinese oyster beds. Cultches are replanted about 2-3 times a year (see plate 6), but storms and typhoons often cause an increase in siltation. In the event that the oyster beds are covered following a storm, the cultches have to be lifted within 72 hours and perhaps less if mortality is to be avoided. Suspended solids concentration following a storm with 18 m/s wind speed increase to 2000 g/m3 (Binnie & Partners, 1984) compared to a normal range of 1 to 164 g/m3.
In deeper waters two techniques are currently in use, the traditional sea bed practice using concrete blocks or stones, or the rafting technique.
Loads of concrete blocks or stones are dumped annually into deeper waters and no further attention is paid to these until harvest. An undefined area in Deep Bay is controlled by the Shajing group of oyster farmers using this somewhat random method. Oysters may be gathered by any farmer paying a small daily fee of RMB$5 to the Shajing group. This virtually common area of deep-water bed may explain the overlap of beds shown in figure 1. A more organised system is carried out by the Nantou group of oystermen with the cultches rearranged after dumping, either by using long tongs or by diving. As visibility is poor and the beds are permanently submerged, rearrangement has to be by touch.
Rock cultches still make up about a third of the total oyster beds. In intertidal areas the rock cultches are less densely packed than the concrete type with rows 1.2 to 1.6 m apart, spaced at 0.45 to 1.0 m intervals.
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