FAO Fisheries & Aquaculture

Food and Agriculture Organization of the United Nations Fisheries and for a world without hunger Aquaculture Department

Fishing Techniques Tuna Trolling Lines

Main Components

Aquatic species

Target Species Tuna market species

Skipjack tuna Albacore Yellowfin tuna Bigeye tuna Swordfish Atlantic bluefin tuna

Target Species Large pelagics

Gear types: Trolling lines Trolling lines

A trolling line consists of a line with natural or artificial baited hooks and is trailed by a vessel near the surface or at a certain depth .

Vessel types: Trollers Troller

Trollers range from small open boats and canoes up to large refrigerated vessels of 25 or 30 meters length.

Characteristics Tuna trolling linesDrawing of tuna trolling lines fishing operation.

FAO Fisheries and Aquaculture Department Species Environment This method is appropriate to catch pelagic fish not too far from the surface and is particularly profitable for the captures of species having high individual value, and where high quality is necessary. Also it requires relatively little investments on gears and vessels and requires fewer fishermen. Trolling lines are used to catch albacore tuna in temperate waters and several tuna and tuna-like species in tropical waters. Albacore and small size tuna normally cruise or travel below the surface in depths of 20 m or more, but will begin to feed when they find a school of small baitfish or other prey. The prey animals normally get driven to the sea surface, where they are also attacked by seabirds. The tuna continue feeding, often for just a few minutes but sometimes for longer, attacking their prey from below, often leaping form the water in the process.

Fishing Gear Fishing by trolling means towing, close to the surface or in midwater, one or more lines with hooks with an attractive bait or lure behind a moving boat. In small-scale fisheries one line only is towed from a canoe/small boat powered with an outboard engine (it is worth mentioning, but it is rare, that, in tropical areas, two small boats can associate for carrying out trolling for tuna in towing between them a line with multiple hooks, longline type; this is "pair trolling"). Within other fisheries, several lines (up to around fifteen to twenty) are towed at the same time from two or more outriggers arranged to hinge outboard from vertical position (when in the port or sailing) to oblique position for fishing. The mainlines are, in general, from synthetic fiber with, as a last part, a short leader, often from fine steel wire (to resist to the teeth of fish) or monfilament line. At the extremity there is a hook, simple, double or triple, in general, barbless, with bait or lure (made from artificial or natural material); to attract fish and induce them to accept the bait, special lures have been designed which either fascinate by their bright colour or so imitate a sick fish by tumbling and whirling movements as to make the predator think it an easy prey. The lines are often, simply, coiled on the deck but on board bigger, modern, trollers each line is stored, shot and retrieve with the help of a small individual line drum; when ten or more lines are used at the same time, there is therefore a series of line drums or sets of trolling gurdies. These may be placed abaft the house or between davits mounted each side of the vessel to support blocks for providing a satisfactory run of the trolling wires to the gurdy spools.

Vessel Overview A part from small-scale trolling from canoe with one or two lines, today's trollers are usually vessels which length ranges between 17 and 30 m and which are characterized by the two poles (or outriggers) spreading almost horizontally on each sides of the vessel when fishing or brought back on a vertical position, when the vessel is resting in port or running towards the fishing grounds. Vessels are normally with a wheelhouse forward arrangement, allowing a clear well or working deck aft. More and more trollers now use hydraulically-powered (Spanish fleet) or mechanically-powered (US fleet) gurdy to bring the fish onboard. When circumstances are favorable, trolling lines can also be operated in sail powered boats. In general, about 6 knots appear to be the optimum velocity for capturing tuna and related species.

Handling Mode Icing. Trolled fish suffer virtually no damage during capture process (except for occasional attacks by predators such as sharks or seals) and can therefore be delivered in excellent condition if the processing on board, if any, and the storage conditions are correct (from the catch to the landing).

Fishery Production Systems Possible exploitation forms using tuna trolling line are: artisanal and semi-industrial

Fishing Environment Trolling lines are used mainly to catch albacore tuna temperate waters (Atlantic and Pacific Oceans) and, for several other tuna and tuna-like species, in tropical waters. Commercial trolling for tunas is usually performed on sea surface and sub-surface where tuna schools are abundant.

Fishing Operations Trolling is a fishing method in which lures or baits are towed behind a moving vessel. A boat drags a set of 5-21 hooked lures through the water at slow to moderate speed (2-10 knots). Tuna attack FAO Fisheries and Aquaculture Department the lures, thinking that they are smaller prey species, and get hooked. One of the most significant development of tuna fisheries in recent years is the widespread use of FADs (Fish Aggregation Devices) to attract and hold surface schooling tunas in a given area. Trolling lines can fish either using FADs either on free schooling. Two main fishing sequences can be distinguished using this fishing technique:

1. Trolling On board a large troller (around twenty meters in length) equipped with outriggers, from 10 to 20 feather jigs with barbless hooks will be towed at the same time. In such cases, the fishing lines are of different lengths and are also spread out along each pole/outrigger to help prevent them from getting tangled up with each other. For the lines attached to the pole, a cord called "inhauled" runs from the line to the boat, so that the fishermen can pull the fishing line to the boat. It is also worth mentioning that for increasing chances to meet target fish as well as to prevent lines from tangling up with the next other, a few lines have more lead than others and are therefore towed at different depths in the water column. Surface trolling speed of about 6 knots appear to be the optimum velocity for capturing tuna and related species, changing the speed of boats, the depth of the hook can be adjusted. Once the line hit the fish, it is detached from the outrigger and comes to the tail of the boat in order to retrieve it in a easier way.

Hooking

2. Hooking When a tuna is hooked, the line is hauled by a fisherman by hand or by a hydraulically-powered or mechanically-powered gurdy. Once to the boat, the fisherman swings the tuna out of the water. The hook is removed from the tuna's mouth and tossed overboard to serve again.

Fishery Overview Tuna trolling lines is a fishing technique used all around the word, particularly from the following fleets: Spain, France, Portugal, Philippines, Japan, Taiwan, New Zeland and USA. Other less important fleets are: Ireland, Morocco, Ghana, Namibia, Panama, Rep. of Korea, Senegal, South Africa and Ecuador.

Fishery Area Trolling lines are used to catch different species of tunas, including: albacore tuna within the Northeast Atlantic, off west of Ireland, Bay of Biscay and around the Azores in the Eastern Atlantic. The method is also greatly in use in the East and South Pacific, including off the west coast of New Zeland and off the west coast of the USA (where trolling is also common for fishing salmon). Regarding tropical fisheries, trolling for tuna or tuna-like species is rather common in Southeast Asia and many other place in the Central Pacific, as well as in many parts of the Caribbean and the Gulf of Mexico.

Seasonality Tuna trolling lines is, in most cases, a seasonal fishing technique following the migration patterns of target species, in particular, in temperate areas. For the fleets of French and Spanish trollers fishing albacore (Thunnus alalunga; in French "germon") the fishing season between West Ireland and the Azores is between May and September with fishing areas constantly moving (as well as the fleets involved!). Tuna normally appears for trolling fisheries in New Zeland waters for the period between November to April (Austral summer and autumn) only.

Issues

Discard Non-targeted fish is seldom captured; it is a very selective fishing method.

FAO Fisheries and Aquaculture Department FAO Fisheries and Aquaculture Department