Fisheries techniques

Page - June 17, 2008
Some fishing techniques have a devastating impact on the other marine life that shares the oceans with the fish being caught. They not only damage marine habitats, but also catch and kill large numbers of other marine creatures, including endangered sharks, turtles, dolphins, sea lions, and seabirds. The most sustainable techniques do not impact on the seabed habitats, and aim to catch only those fish that are the target of the fishery.

Pots and traps

Pots and traps

Pots, traps or ‘creels’ include a variety of designs that take the form of cages or baskets with one or more openings or entrances, with or without bait. They are usually set on the seabed, either singly or in rows, and are connected by ropes (buoy lines) to buoys on the surface to show their position. Animals enter through a one-way opening and then can’t escape.

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Hook-and-line

Hook-and-line

Hook-and-line is a general term used for a range of fishing methods that employ short fishing lines with hooks in one form or another (as opposed to long-lines). It includes hand-lines, hand-reels, powered reels, rod/pole-and-line, drop lines, and troll lines, all using bait or lures in various ways to attract target species.

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Pelagic long-lines

Pelagic long-lines

Long-lines consist of short lines (called snoods) carrying baited hooks, attached at regular intervals to a longer main line that is laid on the bottom or suspended horizontally with the help of surface floats. Main lines can be over 150 km long and can carry several thousand hooks.

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Bottom long-lines

Bottom long-lines

Long-lines consist of short lines (called snoods) carrying hooks, attached at regular intervals to a longer main line that is laid on, or close to, the seabed. Main lines are up to 150 km long and can carry several thousand hooks.

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Pelagic gillnets

Pelagic gillnets

Pelagic gillnets or ‘set nets’ are fine-filament nets that are kept at or below the surface by numerous floats and weights and held in position by anchors. If a fish’s head goes through the net but its body can’t follow, it is ‘gilled’ or entangled in the netting when it tries to get out. Gillnets are used either alone or in large numbers placed in a row.

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Bottom gillnets

Bottom gillnets

Bottom gillnets or ‘set nets’ are fine-filament nets, the lower edge of which touch the seabed, and are held in place by numerous floats, weights and anchors. If a fish’s head goes through the net but its body can’t follow, it is ‘gilled’ or entangled in the netting when it tries to get out.

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Purse seines

Purse seines

Fish are encircled by a large ‘wall’ of net, which is then brought together to retain the fish by using a line at the bottom that enables the net to be closed like a purse.

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Pelagic trawls

Pelagic trawls

The front net sections are often made of very large meshes or ropes, which herd the fish towards the back of the funnel-shaped net. Pelagic trawls may be towed by one or two (pair trawl) boats.

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Danish seines

Danish seines

A fishing net, similar to a small trawl net, with a conical net bag with two relatively long wings. Two long heavy ropes, one attached to each wing, are used to encircle a large area of the seabed to herd the fish into the net and then to haul the net in.

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Demersal otter trawls

Demersal otter trawls

A type of bottom trawl that has two rectangular 'doors' or 'otterboards' to keep the mouth of the funnel-shaped net open horizontally while the net is being towed. A vertical opening is maintained by weights on the bottom and floats on the top.

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Beam trawls

Beam trawls

A type of bottom trawl in which the horizontal opening of the net is provided by a heavy beam mounted at each end on guides or skids that travel along the seabed. On sandy or muddy bottoms, a series of ‘tickler’ chains are strung between the skids ahead of the net to stir up the fish from the seabed and chase them into the net.

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Dredges

Dredges

Similar to a beam trawl, a dredge consists of a rugged triangular steel frame and tooth-bearing bar, behind which a mat of linked steel rings is secured. A heavy netting cover joins the sides and back of this mat to form a bag in which the catch is retained.

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