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Tinned tuna – a quick guide to fishing methods

Posted by Greenpeace UK - 12th August 2008

Purse seined tuna

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. Hook and line fishing is more selective than other types of fishing in terms of species and size, and provides high quality fish. The method can be used on spawning fish as they normally only bite after completion of spawning. Lines are set for a relatively short time so that any unwanted species can often be returned live to the sea.

Hand-lines use lines and baited hooks from a stationary or moving boat. Because hauling is slow, mechanised systems have been developed to allow more lines to be worked by a smaller crew.

Pole-and-line, or ‘bait-boat’ fishing, attracts surface-schooling fish to the vessel, where they are driven into a ‘feeding frenzy’ by the throwing of live or dead bait into the water and the spraying of water onto the sea surface to simulate the escape of small prey. Lines are used to hook the fish, which are then pulled on board by manual or powered devices.

Trolling uses lines fitted with baits or lures that are trailed near the surface or at a certain depth by a vessel. Several lines are usually towed at the same time.

Fish Aggregating Devices: in the natural environment, marine life is attracted to floating objects like broken trees. FADs are designed to replicate the effect of such natural fish aggregators, except that they can be sophisticated steel structures, anchored to the sea floor and fitted with electronic monitoring equipment that can transmit detailed information to fishing vessels by radio, including water temperature and quantity of fish in the vicinity.

Purse seining involves fish being 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. This method can be highly specific, with little bycatch, when targeting adult schools of one species, but at worst when set on fish aggregation devices or FADs, the resulting bycatch of juvenile tuna and other marine life is high.

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 100 km long and can carry several thousand hooks. Long-lines catch many endangered sharks, turtles, marine mammals and seabirds. Bycatch can be reduced in a variety of ways including circle hooks to prevent catching turtles, and setting deeper lines to reduce catches of turtles, sharks and marine mammals. Techniques such as setting lines quickly and at a greater depth, using bird scarers, and setting at night can reduce the number of seabirds that get caught on hooks and drown when diving for bait.

Article Tagged as: Tuna