6.2.1 Background

On the Pacific coast of North America most oyster production is from intertidal bottom culture and more recently floating culture. Originally juvenile oysters were imported annually from Japan and spread on a grower’s lease for growout.

Juvenile oysters were set on bivalve shell, usually old scallop shell, but this supply of seed ended when it became too expensive. Breeding areas were located along the Pacific coast and used to augment seed imported from Japan and eventually to replace it. Oyster larvae were generally set on bivalve shell, mostly old oyster shell, and allowed to grow on the shell in breeding areas until the juveniles attained a shell length of about 1 cm at which time the cultch with attached juvenile oysters was transported to a grower’s facility. In intertidal bottom culture the seed was spread either directly in growout areas or held on seed ground for upwards of a year and then spread in growout areas. In floating culture the cultch with juveniles could be strung on wires or ropes and suspended from floats or longlines. The method was generally effective for reliably supplying growers with their seed requirements, but there were disadvantages with the system.

The main disadvantage was that failures or insufficient breeding occurred in breeding areas in some years. Consequently growers did not have sufficient seed for growout operations. Cost was another problem. Shell is bulky and heavy and it was expensive to move large quantities of juveniles attached to oyster shell. Another disadvantage was that the seed could generally only be moved during the cooler, wetter months, October and November, and this was frequently inconvenient for a grower who wanted the seed at other times, particularly during spring and early summer. It was also impossible to select for a particular strain or race of oyster in natural breeding areas.
Studies showed that mature Pacific oyster larvae with well developed eye spots could be held out of water in a damp but cool condition (5-10°C) for upwards of a week. Thus it became possible to ship mature Pacific oyster larvae considerable distances, literally anywhere in the world. A grower could purchase mature oyster larvae from a hatchery whenever it was convenient, have them shipped to his/her facility and set them on the preferred type of cultch used in their growout operation. The disadvantages of previous techniques including reliability of a seed supply, cost of handling bulky cultch with attached juveniles and not being able to obtain seed when desired, could be averted. Further, a grower did not have the expense nor time consuming effort to build and operate a bivalve hatchery. The method, now widely used by growers along the North American Pacific coast, provides a convenient and efficient way to ensure a reliable and plentiful supply of oyster seed for culture operations.