I have received several requests for more information on the Australian Adjustable Longline System (ALS) for oyster growout. Experienced oyster growers are justifiably fascinated by the potential of this system. It was designed, tested and implemented by three oyster growers from South Australia. It resulted from studying the problems of the traditional rack and bag system, which is very common in Europe and some areas of North America.
The primary disadvantage with rack systems on inter tidal zones is that they allow for a period when the animals are out of the water. The lack of food and increased stress during low tide contributes to a slower growth cycle. To overcome this it makes sense to operate in sub-tidal zones when using bottom fixed gear. But the problem here is bio-fouling of the gear and the oysters within.
The innovative solution devised by the South Australian growers is a longline system that's deployed in the subtidal zone, with 2' to 4' of water at low tide. Once you look at all the features of this system, it's easy to see that Mother Nature is doing about 85 percent of the work.
The system is made up of a special Veclock longline to which growout bags are attached. The longline is supported by a grid of poles which are fixed in the bottom. The grid is set up in a design that allows easy access for deployment and harvest, using specially built flat bottom outboard motor barges. Two people can install 300 meters of longline in about six hours.
Cylindrical open mesh baskets are hung from the longline using special clips. The growout baskets are able to swing back and forth freely in any wave action. This swinging motion provides the benefit of tumbling the oysters. Tumbling causes a pruning effect, which gives a very symmetrical shape to the animals and helps cup the shell for the half-shell market.
The tumbling action also allows for another benefit. Oysters grown in protected gear that are constantly in the water column normally have a thin, more brittle shell that creates problems when the oyster is opened. To fix the problem, growers using trays or lantern nets below rafts or longlines have to relay the animals onto the beach for two to six weeks. There the oysters acclimate and toughen the shell so they are acceptable to the market. The problem however, is that this adds extra labour cost. With the Australian system, the tumbling action replicates the natural environment of wave action and predation-prone areas, which causes the animals' shell to toughen - all without extra labour.
The real plus of the system, though, is spelled out in its name, Adjustable Longline. Four or five special plastic clips are attached along the length of each pole of the grid. Thus the placement of the longline can be raised or lowered depending on your needs.
With the longline at the bottom clips, the baskets are in the water all the time at low tide. If it's on one of the middle clips, the baskets would be at the surface at low tide. And if it's on the top clip, the baskets are out of the water at low tide. What this means is that now you have a biofouling control method.
In the spring of the year (fall in the Southern Hemisphere) when the water temperature is low and the angle of the sun causes deflection of direct sunlight off the water, bio fouling is at its least. You'd use the lowest clips then, so the growout baskets were always in the water for maximum food availability to the oysters.
As the summer months approach and the water warms due to the increased angle of the sun, which causes deeper light penetration, biofouling increases. By having the baskets in the mid position, wave action and partial exposure to the sun will help clean the bio fouling.
In the late summer when bio fouling is at its peak, the baskets are at the top position and out of the water at low tide. Sunlight then decomposes the biofouling, which is dispersed by wave action during the rest of the tidal cycle.
To adjust the longline height takes one hour or less. When you consider you many have to do this only four to five times during the growout cycle, that's a very low labour cost.

Cost Analysis

Seed is put in the baskets after nursery stage or using fine mesh baskets inserts, which allow deployment shortly after hatchery stage. Special plastic wire, which is part of the clip hangers, is also used to hold the folded basket ends closed. This allows for quick and easy loading and unloading of the baskets.

In some locations, existing pier pilings could be used instead of installing the gird of posts. Use of common sense to evaluate the site with respect to water quality and expected output returns.

The average cost of a 300 meter, 300 basket system including locally sourced poles and labour is around $4,000.

If you stock oysters at 150 per basket and you receive an average of 25 cents per oyster, farmgate price, this would produce 300 x 150 x 25 cents or $11,250 gross income. The first cycle gross profit figure is $7,250. Of course, expenses have to be deducted, but you can see the potential for a good net profit too.

With a gear life expectancy of approximately seven to ten years and using an area of a lease that due to labour cost would normally not be used, some growers will find the system a welcome bonus to their operation. The system is currently available for spring delivery from a number of aquaculture suppliers in the US and Canada.

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Contact Don Bishop at:
Fukui North America

110-B Bonnechere St.W.
Eganville, Ontario K0J 1T0
CANADA
Email: don@bishopaquatic.com or call 613-639-3474

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