Oyster Culture TechniquesThe four most common oyster culture techniques in the Pacific Northwest are:
Beach culture is the simplest and most common method of growing oysters in the Pacific Northwest. Generally, oyster spat is purchased from a hatchery and spread onto a farms beach in the intertidal zone. Spat can be purchased at different levels of development, with the more mature product costing the most. Once spread onto the beach, spat are vulnerable to natural predators like crabs, starfish, birds, and oyster drill snails as their shells are still very thin. To overcome this, some farms will cover the spat with netting or put them into fenced pens. Beach culture produces the slowest growing oysters, as they are subject to wind, wave, and tidal abuse that tend to wear away their fragile new shells. They end up being the thickest shelled oysters, and usually the easiest to open, because of this slow growth. They tend to be grayish in appearance, as the sun bleaches the color out of their shells over time.
Bag culture is also common. Large mesh bags containing oyster spat are attached to lines that are in turn staked to the beach in the intertidal zone. The oysters are considerably more protected than those that are beach cultured, as the mesh bags keep many predators at bay and will also protect the oysters from some of the weather abuse that slows their growth. In addition, it will block a significant amount of the sunlight that bleaches the color out of their shells. Predictably, the shells of bag cultured oysters are thinner than those of beach cultured oysters, and their appearance is more liable to include some combination of blues, purples, tans, browns, and whites, depending on the mineral content of the water in which they are grown. These oysters will mature more quickly than those that are beach grown, however, this method is more labor intensive. In order to produce oysters that get the increased growth rate and that are well shaped, the bags must be thinned out regularly as the product grows in size, and they must be flipped over numerous times to keep any prevailing winds or currents from piling the oysters into one end. Oysters left piled together will grow much more slowly, and worse, they will grow poorly shaped… long thin (snaky) shells, shells without much cup, or shells with their hinges wrapped around underneath them.
Many farms now utilize a combination of these two methods, starting spat in bags and then transferring them to the beach as they get a little bigger and heavier. By allowing oyster spat to start in bags on the beach, a farm can increase their survival rate significantly. By allowing them to finish directly on the beach, they allow the oysters time to develop harder shells and stronger adductor mussels, while saving themselves the time and expense of dealing with the bags as the oysters start to increase in size.
Suspended culture involves hanging nets or trays containing spat from some means of flotation system. Rafts, buoys, and long lines supported by a series of buoys are common means of achieving this. Oysters grown this way are not in the intertidal zone at all, but are in the water all the time, rising and falling with the tide. They are well protected from most predators, and get no exposure to the bleaching effects of the sun that would otherwise dull their appearance. Suspended culture oysters grow the most quickly, as they are feeding 24 hours per day, seven days per week. This is a real plus for an oyster farm, since they are turning their investment in spat back into cash very quickly, but it involves a compromise. This growing method produces shells that are thinner than either of the other techniques mentioned, and one must be careful not to chip their fragile edges. In addition, it produces oysters that have weak adductor muscles. Oysters use their adductor muscles to keep their shells tightly closed when they are out of the water. Without the daily exercise that Mother Nature provides intertidal oysters, the muscles of suspended culture oysters are comparatively weak. They will tend to open up and dry out more quickly than oysters cultured intertidally, but most farms growing suspended culture oysters attempt to overcome this by packing their oysters in boxes cup side down. By doing this, they minimize water loss when the muscles do relax, as the liquid in the deep bottom cup is trapped. Farmers utilizing this technique must, like those using the bag technique, keep their trays or nets thinned out, as high densities create poorly shaped oysters.
Dike culture involves building low rock or cement walls around pools to keep the water in when the tide goes out. Diking portions of the intertidal zone ensures that the oysters are always covered by water. This allows them to feed continuously while protecting them from freezing in the winter and from getting too hot in the summer. Dikes are used primarily in the culture of Olympia oysters.