Tray Culture Systems
One of the most productive methods of off-bottom culture of single oysters is by means of trays suspended from rafts or long lines. These systems are also widely used for rearing juvenile clams up to the point where they must be seeded on a beach.
Over the past twenty years several types of trays have been used in British Columbia and one of the major objectives has been to achieve high levels of efficiency in large scale production systems. Trays require a strictly planned approach to oyster culture because they are relatively labour intensive and cannot be ignored or neglected for any length of time. The pay back is faster growth and good quality products when these systems are well-managed. Properly grown tray-raised oysters are ideal for the half shell market, where they may be sold to restaurants or fast frozen in the half shell and sold in retail outlets. They are a particularly attractive animal to market because they are deeply cupped with a large amount of meat. Delicate fluting of the shells makes an attractive presentation in the restaurant or supermarket. To produce the kind of oyster that can command a high price requires strict control over the culture process.
Nestier and McNichol Trays
Several tray designs have been used in British Columbia for oyster production. Adequate water flow through the tray is critical to obtain maximum growth rates for the oysters. Poor flows mean less nutrients. The Nestier tray, below, was designed so that oysters could be spread in a single layer in the tray, and trays fit into one another to create a tray stack, essentially a multi-storey oyster dwelling.
It is sometimes difficult to achieve adequate water flow through these trays which means full growth potential of the oysters may not be realized. Nestier trays are usually tied into stacks using some kind of strapping material which must be undone when grading or harvesting oysters. If the stacks are to be hung from rafts or long lines., special rigging must be devised to keep the stacks hanging vertically in the water. These trays are also used as nursery rearing chambers for clams and singly oysters. Fiberglass window screen material is glued on the inside surface of the tray.
Another second type is the McNichol tray. These are donut-shaped trays ribbed on the inside to form three growing chambers. These trays can also be stacked by inserting a large diameter (6″) piece of PVC pipe through the tray centers and holding the stack together by inserting pins through the pipe at the top and the bottom. This must be dismantled to access tray stacks for grading and harvest. These can be suspended from rafts and long lines. by means of the center pipe and will hang vertically in the water.
The desire to increase capacity and efficiency has lead to the development of two new tray designs in BC:
Dark Sea and High Flow trays.
These trays are based on the principle that single oysters will grow optimally in single discrete layers. As long as densities in the trays are controlled, oysters should not cluster and grow onto each other. With adequate spacing, the oysters grow rounded and deep-cupped.
The dimensions of the trays are about two feet by two feet by 3 inches (8cm) deep. The mesh of the trays is wide enough to allow good water flows. The tray is divided into four sections by Elevated diagonal ribs across the bottom of the tray divides it into four sections. Cut-corners help prevent piling of oysters. The trays are stacked over a central spindle and are held in place by posts in each of the cut-corners. The stack is secured and hung by the spindle from long lines. or rafts. Attachment at the the center ensures the stack hangs vertically.
A second tray design was introduced in 1997. It is a tray intended for high density production of single oysters. The trays are much deeper than previous designs allowing them to hold large volumes of stock. Each tray might be stocked with ten dozen oysters at small or extra small harvest size. The trays are open to allow maximum water flow around the oysters to promote very high growth rates. Handling efficiency was a primary consideration in the design.
They are intended to be used primarily on raft systems, where tray stacks can be readily hauled up and dismantled for grading or harvesting. Dismantling the stacks is done by pulling up the center cross-piece and popping the line out of each corner clamp on the trays. A dome will cover the top tray of each stack.