Vónin’s new sorting system for pelagic fishery is designed to improve profitability and consists of a four-sided net tunnel with a flexible grid fitted inside. This sorts larger fishes from, for example, blue whiting and herring. The larger fish that do not pass through the grid, escape through an opening in the bottom.

The tunnel is manufactured from nylon netting and has a sorting section that is 20 metres long and is arranged between the belly and the bag. The sorting grid itself is held together by strong Dyneema twine and since the twine does not stretch at all, the grid maintains its original size. The distance in of the grid opening depends on a customer needs. The grid is manufactured to the shape of the tunnel and is attached to its sides. The tubes have superb flow characteristics and are fully stretched while towing. The grid is mounted at an angle of 45-60° and underneath it there is a chafing mat, attached under the opening where the larger fish escape.

Advantages

The greatest advantage with this grid, compared with the usual steel and plastic grids, is that the sorting grid does not need to be handled carefully while recovering the gear on board, as the sorting section is reeled on to the net drum along with the trawl, without suffering any damage.

This advantageous type of grid, which is used worldwide in the fish farming industry, has now, for the first time, been tested and used as a sorting grid on pelagic trawlers while fishing blue whiting.

This flexible sorting grid was invented and developed for the fish farming industry a few years ago by Johnson Seafarms Ltd, of the Shetlands. In 2005, the Faroese trawl manufacturer Vónin re-developed the flexipanel for use as a sorting system for pelagic fishing.

At sea trials

Vónin, together with the Faroese Fisheries Laboratory, collected the data by joining the pelagic vessel trawlers Christian í Grótinum and Næraberg from Klaksvík, Faroe Islands on the fishing grounds.

In this research an underwater camera was used, which was attached in front of the grid. Also the trawlers were fishing with and without a sorting grid, to see what amount of by-catch was going through to the cod-end.

The steel grid had a good water flow while towing, however, this grid is easily bent and the space between the grid sections becomes unevenly distributed. The steel grid is not flexible to handle easily on deck.

On the other hand, the plastic grid is very light and the grid sections bend rather than break. However, as the water flow is not good, a lot of fish circulated in front of the grid and in the tunnel side.

The new flexible sorting grid had good water flow characteristics and was very flexible while being towed. Moreover, the grid was very flexible to handle on deck.

As highlighted, the sorting section has been on trial on board pelagic vessels, and complies with all demands set for pelagic fishery.

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