Archived – Tougher cage systems the goal of East Coast research

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Most people who have not seen or experienced it themselves really have little idea of just how brutal ocean conditions can be for fish farming on the East Coast of Canada, according to the general manager of a net pen construction, design and repair company in the region.

So GMG Fish Services Ltd., a subsidiary of Cooke Aquaculture, has an ongoing program to work with scientists and researchers to continually improve net pen cage-system designs for the salmon-farming industry. The program is based out of the company's net-pen design and manufacturing facilities in St. George, New Brunswick.

GMG Fish Services GM Alan Cook has experience with fish-farming on both the Canadian West Coast and East Coast, and he says there is truly little comparison between what East Coast farmers have to contend with, and the much more sheltered conditions on the West Coast.

In particular, said Cook, many of the East Coast farm sites are exposed directly to the open Atlantic Ocean, so the "fetch" or distance over which wind and waves can build is considerable.

To counter that, GMG has been working with the Institute of Ocean Technology's Dr. Bruce Colbourne in Newfoundland to come up with ways for net pen mooring attachments to absorb more of the shock from waves and currents.

The research, which is supported by the Industrial Research Assistance Program of the National Research Council, is aimed specifically at coping with extreme conditions in a deep-sea farming setting.

Tests are continuing on aspects such as different mooring-grid depths, the effect of weight rings, and a modified bird-net stand to handle the heightened problems East Coast farmers have not just with cormorants but also with seals.

Cook said that one of the big problems for East Coast fish farmers is that waves that measure three to four meters from crest to trough are not an uncommon feature on the coast.

"Those are significant waves, and you can get them 10-metres high in the open ocean out here," he said, adding that currents of two knots and more are also a comparatively frequent occurrence. Heavy ice loads in winter also have to be taken into account.

So GMG has been working with the institute to improve net-cage systems so they can handle that kind of marine assault, using a scale model of cage systems in the institute's 100-by-30-metre wave-simulation tank.

"We're trying to adjust improvements to the mooring systems, to reduce the shock loading on the moorings from high waves and currents and find ways to control the motion of the bottom panel of the net," he said.

Cook, who recently made a presentation on pen design to a conference on off-shore fish-farming in New Hampshire, said that one way East Coast fish farmers try to control or reduce the motion of the bottom of the net is through using weight rings, but he thinks that few people have much experience with them.

He also noted that there is a considerable difference between the submerged, research sized open-ocean cage systems which have drawn so much attention off the United States, and the industrial-scale cages GMG makes - mostly, to this point, for internal use within Cooke Aquaculture.

"The design and the materials (for the submerged systems) won't allow them to be scaled up to the high-volume output size the industry wants and needs," he said. He said to scale them up to that - from roughly 6,000 to about 10,000 cubic metres - would hike the cost of the materials to about $30-35 a cubic metre, which would be prohibitive.

Submitted by the Institute of Ocean Technology. For more information contact Bruce Colbourne (Email: D.Colbourne@nrc-cnrc.gc.ca)

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