|OverviewLonglining is a passive type of fishing technique making use of lines with baited hooks as fishing gear.
Species EnvironmentLongline are used mainly to catch large bigeye tuna
albacore tuna and yellowfin tuna in tropical waters as well as northern bluefin tuna and southern bluefin tuna, swordfish, marlins in temperate waters.Fishing GearThe longline used for tuna fishing is made up of units (sometimes known as "baskets"), each of which consists of a main horizontal line about 250 to 800 m long with 4 to 15 branch-lines, each with a wire leader and a hook. The depth where the hooks are set in the water column is a crucial element, this depth in which the longline is settled can be regulated mainly by modifying the intervals of the main line between float lines and partially by adjusting the length of float-line and/or the speed of shooting, to a lesser extent, by modifying the length of the branch-lines.Vessel OverviewIndustrial tuna longliners are usually large vessel with length ranging between 30 and 70 m. The basic requirements of a tuna longliner, industrial type, are: adequate speed to reach far away fishing grounds, enough autonomy (fuel, water, accommodation of crew, etc.), capacity for operating in the high sea (sometimes very rough seas at cold temperature), facility for very efficient freezing storage (to attain extremely cold temperature under 45°C) to keep the highly valued tuna for months together, suitable deck arrangement and equipment, protection of crew from rough weather and sea conditions, machineries for shooting and hauling up longlines quickly and proper storage facilities for keeping the fishing gears and accessories. These large specialised vessels can stay away from their home ports for 10-24 months.Fishery Production SystemsPossible exploitation forms using tuna longlining are: industrial and semi-industrial.Handling ModeIf the vessel's cruise is less than a month, the tuna can, in principle, be stocked directly in isolated fish hold. However, nowadays the large commercial tuna longline vessels use to stay at sea for months (sometimes up to almost a whole year). In such situation, the catch has to be frozen (in perfect conditions for maintaining top quality for the product). Hence it is necessary to extract blood, pre-cool, freeze and install fish in a store at a temperature of -40°C to -60°C. It is very essential to freeze the fish meat to such a low temperature so as to retain the quality and colour of the meat for a very long period.Fishing EnvironmentTuna longlining is carried out in open waters including in the high sea. The hooks fish in sub-surface areas and at depths of about 100 to 300 meters (maximum depths of 175 m for the conventional longlines and of 300 m for the deep longlines).Fishing OperationsTuna longlining is a passive type of fishing technique making use of lines with baited hooks as fishing gear. Midwater longlining allow catches of fish in midwater and near surface (while casting and retrieving). Midwater longlining for tuna (which would be originated from Japan) is now a widely used method for catching tunas in the depth range from the subsurface up to 300 m (the most common method with purse seining, the later being more appropriate when tuna are grouped in large schools and, normally, not deeper than one hundred meter). A typical set consists of 200 or more units or "baskets" connected together, with a buoy at each connection, and a total of about 3 000 hooks. The details of the fishing operations, manoeuvres, given below are included only as example since they reflect specific conditions: vessel size and equipment, crew and fishery conditions.|
|1. Baiting longlinesThe baiting of hooks may be manual or made by (baiting machine). Traditional bait is sauries. Depending on the target species, squid and various species of fish (e.g. mackerel) are used for bait. In the manual baiting operation, the crew member responsible for attaching the bait to the hook, does so by piercing the bait by the hook at the time of casting the branch line just before being connected (clipped on) to the main line by another member. The baiting machine is usually located aft of the line storage rails. The bait is fed into the machine via a spiked conveyor belt. It is essential that the bait be firm as it helps to ensure a good hooking rate. Before the line is set the bait is removed from the freezer and thawed partially before use. Baiting machine are usually designed to bait 10-20 000 hooks a day.|
|2. Setting longlinesA typical set consists of 200 or more "units/baskets" connected together, with a buoy at each connection, and a total of about 3 000 hooks. Generally branch lines are stored separately and attached to the main line while casting the line, each hook being baited just before leaving the vessel's deck. The vessel steams at between 9.5 knots and 11.5 knots. The longline is paid out from the aft storage wells on the upper deck through a series of PVC pipes and a hydraulic line feeder, situated on the lower deck amidships, at a rate of about 450 m per minute (27 km per hour). The depth of the mainline can be varied mostly by the distance between which the buoys are attached to, and also by changing the speed of the feeder and the speed of the vessel. The rate at which branchlines (snoods) and buoylines are attached to the mainline, and therefore the space between snoods, is controlled from the wheelhouse. Radio buoys are used for locating the line at the start of the haul or in the event of a broken line. Between 2 500 and 3 000 hooks are set over a total distance of about 100 km, taking about five or six hours to complete each set. At least five crew members are required for the setting. After the last radio buoy is set, the crew retire for about four hours before the start of the hauling operation. In general the starting time for hauling the lines depends upon the number of baskets set.|
|3. Hauling longlinesHauling usually takes at least a full day (11 hours and more) and requires a line hauler and a dozen crew members or more. The last radio buoy set is usually the first to be hauled on board. It is located with the help of the radio direction finder or by radar, and is hauled on board and detached from the mainline. The mainline is threaded over roller guides and through the hydraulic mainline hauler. The speed of recovery is controlled by a crew member. The mainline coils under its own tension from the hauler onto a conveyor belt which carries it across the deck from starboard to port side. Any tangles in the mainlines are removed as it moves along on the conveyor belt. The vessel steams along the mainline at an average speed of about 6 knots, with the line retrieved over the starboard side at a rate of between 150 and 250 m per minute. Branchlines are unclipped off the mainline as they come over the side of the vessel or after they go through the line hauler. The snoods are coiled, either by hand or with an automatic coiler, and are tied off around the hook with a loop of the line near the clip, then packed into bundles of about 20 or into baskets. These bundles or baskets and the buoys are placed at intervals onto a conveyor belt on the port side of the vessel. This takes them to the crew member who is packing the mainline into the aft wells and they are then stacked at the stern ready for the next set.|
|4. Landing catchWhen a large fish is detected on a line, the vessel slows and may turn to starboard to follow the fish. When the fish is brought alongside the vessel, a gaff or a harpoon is used to land it, preferably avoiding spearing the fish in the meat part. Once landed, the monofilament line is cut so the hooks remains in the mouth until dressing. This practice reduce the time a tuna may spend on deck in a stressful situation, and makes handing of the catch much easier.|
Fishery AreaTuna support a very important commercial longline fishing throughout the tropical and temperate oceanic waters of the world. Particularly, Northern Eastern Pacific; Southern Eastern Pacific; Western Central and South Pacific; Eastern Indian; Western Central Indian Ocean; Eastern Atlantic; Western Atlantic; Central Western Atlantic, Western Mediterranean (Tirrenian, Ligurian, St. Sicily); Western Mediterranean (Aegean, Marmarra).Fishery OverviewA large fleet of industrial tuna vessels is operating with midwater longlines in the Indian Ocean and in the central and southern Atlantic and Pacific Oceans. The fishing method was perfected by the Japanese in the 1930s, but its use did not spread outside Japan until after Second World War.Fishery OverviewThe Japanese longline fleet mainly target yellowfin tuna and albacore until about 1970 to supply the growing US canning industry. Then the fleet gradually switched to bigeye tuna, which currently accounts more than 60% of the catch. The shift was driven by economic and market forces. Tuna longlining is a fishing technique used all round the world by the following fleets: Taiwan, Republic of Korea, Indonesia, France, USA, Canada, Province of China, Chile, Spain, Philippines, China, Belize Honduras, Panama, India, Iran, Sri Lanka, Maldives, Netherlands Antilles, Seychelles, Lybia, Portugal, Liberia, Ghana, Namibia, Senegal, South Africa, Ecuador, Morocco, Ireland, Brazil, Venezuela, Uruguay, Italy, Malta, Tunisia, Croatia, Cyprus, Greece, Turkey.IssuesDiscard Tuna longlines have possible environmental side-effects (even if less than many other fishing methods), particularly in terms of unwanted catch (incidental catch) of non-target species or juveniles, endangered species such as sharks, turtles and seabirds (especially albatrosses and petrels), (see IPOA's Seabirds and Sharks).
|5. Fish handling on boardA live catch lifted on the deck must be killed on the spot, because it is very dangerous for the crew to work beside the live catch that goes on jumping madly on the deck as well as to keep the quality of the meat in a good condition. With tuna, the caudal fin is removed immediately with a saw, all the fishes are disposed of to the freezing chambers but only after gutting (removal of gills and guts). All the catch are washed and put in the pre-cooler room.|