In the 1960’s Pacific oyster (Crassostrea gigas) hatcheries were established in the UK. These were set up to rear Pacific oyster spat for relaying in commercial farms. The industry had been experimenting for some time with various species of oyster and had chosen the Pacific oyster because it does not spawn regularly in our cool waters, it is robust and grows to a saleable size in about 36 months. The Pacific oyster has proved very successful, it grows well and is robust enough to be handled by shellfish farmers.
The Pacific oyster is farmed in the Rivers Teign, Exe, Dart, Avon, Yealm and Salcombe-Kinsbridge Estuary in Devon. The spat is bought in during the early part of the year, when they are about the size of a five pence piece, and placed into mesh bags, with about 500/600 per bag. Because the oyster is a filter feeder the bags are placed on racks in the intertidal zone, the closer the better to allow the oysters to be submerged and thus feeding for as long as possible. The bags are left on the estuary only being turned over and shaken occasionally to prevent the oysters from growing together, or though the mesh.
After 6-8 months they are brought off the racks and graded according to size and replaced into larger meshed bags. The number per bag is also reduced. The oysters are then placed back onto the racks to continue growing. The spat grows at different rates, this can be due to climatic factors or availability of food, also some individuals just grow faster than others. The faster growing individuals reach a market size of 80-100g in 18 months whilst others take up to 30 months.
Another method for growing Pacific oysters, also used in the Teign Estuary, is the PARC system. The spat are placed on the river bed and left to grow to marketable size. The oysters grown in this system are more liable to predation both from humans and animals. Due to the filter feeding of the oysters and the need to keep them submerged for as long as possible, the oysters can only be worked on during spring tides in most areas, therefore the fishermen only work on the rivers every other week and only for the limited time of the low water period.
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