Scallops

Scallop farming has only recently been developed in BC. Although the potential for a large viable culture industry is significant, the production of farmed scallops remains relatively small. There are several species of native wild scallops that are occassionally harvested on a very small scale: the Weathervane Scallop (Patinopecten caurinus), Rock Scallop (Crassadoma gigantea), Pink Scallop (Chlamys rubida), and the Spiny Scallop (Chlamys hastata). However, the natural abundance of these species is insufficient to support either a commercial fishery or seed collection for culture. Although the potential for hatchery production for these species has been realized, the growth rates of these native species is slow and presents a barrier to feasible culture operations. The Japanese Scallop (Patinopecten yessoensis) was adopted for culture in BC and seed are hatchery produced for grow-out operations in Georgia Strait and the west coast of Vancouver Island. Recently a superior hybrid of the Weathervane and Japanese scallop has been developed for culture in British Columbia by Island Scallops Ltd.

Seed
Unlike Japan or the Atlantic coast, the culture of scallops on the Pacific coast relies entirely upon hatchery production of seed. Seed production methods were first investigated in the 1980’s by researchers at the Pacific Biological Station in Nanaimo. Commercial production of seed was subsequently developed at Island Scallops Ltd.

Scallop broodstock are conditioned in tanks by manipulating water temperature, photoperiod and feeding so that they spawn at a predictable time. The larvae are reared in a tank and fed algae until they are ready to set (21-28 days). At this stage they are about 250 microns and have a distinct eyespot and foot.

Setting is done either in the hatchery or growers may be equipped with setting tanks on site to do their own remote setting. Seed collectors are put in the tanks to which the setting larvae attach. The seed collectors are usually spat bags filled with a collecting material (e.g. kinran). Growers can then take these seed bags, usually filled with about 1000 seed per bag, and transfer them to the growing site for nursery rearing. This would usually be done in April or May.

Nursery and Intermediate Culture Stages
Scallops are well known to have relatively low tolerances for temperature and salinity fluctuations. During the early post-set stage, the juvenile scallops are particularly prone to mortalities. Gill are not yet fully developed so they do not filter feed yet. They use the foot to probe around in the detritus and transfer food to the mouth by cilia. When the spat are transferred to an ocean nursery site it is important to put them deep enough to be free of temperature and salinity fluctuations yet making sure they have access to plankton in the water. The spat bags containing the scallop spat are transferred directly from the hatchery to the nursery site and fastened onto downlines attached to a longline. Eight bags may be attached to each downline at one meter intervals and downlines are spaced one meter apart on the longline. The scallops grow in these bags until mid-summer when they reach a size of 1.0-1.5cm and they detach from the collecting material.

Scallops are graded by sieving through a screen and transferred to pearl nets, which consist of a plastic coated frame surrounded by plastic mesh, usually 6mm mesh size.

It is critical to stock the pearl nets at sufficiently low densities. Scallops do not tolerate crowding well and will damage eachother if they are too densely stocked. Commonly called “biting disease”, scallops will clap their shells to move or expel material and, clipping other scallops in the act if they are too crowded causing damage to the mantle and usually mortalities. A density of not more than 60 1.0-1.5cm scallops per net is recommended, based on the size to which the scallops will grow in the pearl net when they are sorted the second time (3.0-3.5cm). At this density, an additional sort before transfer to to lantern nets is not necessary unless biofouling becomes a problem. This will reduce labour and handling stress on the scallops. Once they are stocked, pearl nets are fastened one on top of the other and the line of approximately 15 nets is then tied to the longline, again deep enough to avoid temperature and salinity fluctuations, usually 5-15 meters below the surface. Length of time in the pearl nets depends on the rate of growth of the scallops, but under good conditions they may reach the 3cm size by September.

Growout
Once they have reached the 3cm size, the scallops are removed from the pearl nets, graded and either ear hung or put into lantern nets. Stocking density is again critical for lantern nets. Depending on the diameter of the net, scallop density should be calculated on the basis of size at harvest (8-10cm) such that no more than half the surface area is covered by the scallops. Lantern nets usually have 10 tiers and hung individually on the longline.