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

Fishing Techniques Tuna Drifting Gillnet

Main Components

Aquatic species

Target Species Tuna

Skipjack tuna Albacore Yellowfin tuna Swordfish Atlantic bluefin tuna

Target Species Big pelagics

Gear types: Drift gillnets Drift gillnets

Drift gillnets consist of a string of gillnets in general drifting with the current near the surface or in mid-water.

Vessel types: Gillnetters Gill netter

Gillnets can be operated from boats and canoes on inland waters and inshore, decked small vessels in coastal waters and from medium sized vessels fishing offshore.

Characteristics

Species Environment Drifting gillnets are used to catch albacore tuna and other tuna species and are also used to catch swordfish (in the Mediterranean Sea off African coast and off Baja California). 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 from the water in the process. FAO Fisheries and Aquaculture Department Fishing Gear The drifting gillnet is a wall of fine, large-meshed synthetic netting with a line of corks at the top and a series of leads or a steel chain at the bottom to maintain it vertical in midwater, in general, not far below the surface. It is normally set at dusk and hauled at dawn. The length of drifting gillnets deployed by fishermen targeting tuna or other large pelagic fish such as swordfish are commonly several kilometers whereas the height ranges from 20 to 30 m.

Vessel Overview Gillnetters are, in general, medium-size, ranging from around 10 m to more than 20 m long vessels. Their wheelhouse may be aft but, more often forward to leave enough space for storing very long nets. The shooting is, in general, from the stern and the hauling by the side. On the smallest boat there can be some hauling by hand but, in general these vessels setting and hauling operations are performed by hydraulic net hauler or net drum.

Handling Mode Wet-fish or frozen fish. Fish may be kept for a few hours on the deck with cover sprayed with sea water to lessen dehydration; more often, the fish is iced in fish hold; on modern fishing units, even rather small one, the tuna will be frozen, either full fish or in filets.

Fishery Production Systems The main exploitation forms using tuna drifting gillnets areartisanal or semi- industrial fisheries.

Fishing Environment The drifting gillnets are, normally, used for catching small schools of tuna and tuna-like fishes swimming not far from the surface; it is worth mentioning that the bigger individuals are usually found swimming in deeper waters.

Fishing Operations The tuna drift gillnet is a passive fishing gear, fish passing by is captured by gilling or entangling in the vertical net webbing. The gear is very popular among the small-scale fishermen since it is simply constructed and very effective in catching tuna.

1. Setting The boat searches for a good fishing area, first. At the fishing ground, the current and wind directions are determined through the movement of the boat when left a drift or a line. The net is usually set diagonally across the current. Several fishermen are involved in setting the net, at least, one takes care of paying out the floats and upper part of the net, and another is in charge of the middle and the lower portion of the net. During the shooting, the boat is steered as it goes with the current as the net is layed- out. When all the pieces of nets attached one to the other panels have been shot, the end of the last one can be connected to the boat and both will drift together. Such gillnets are often left fishing during a whole night. However, in the meantime, patrolling is sometimes done every two three hours to determine if there is catch. Indication of fishes gilled is through submerged or tilting the floats. When there is fish at a certain point of the net, the floats at this point and the portion of the net are hauled to get the catch and ungill the fish; after, the gillnet is put back into place in the water.

2. Hauling Hauling the gillnets often starts at dawn. The first light marker or buoy is hauled first and followed by the net. The net is on board most of the vessels haul with the help of a net hauler or power block, one crew member on the headrope and another on the lead/footrope. Fishes caught are ungilled, taken to the shaded area if there is much sun and, if it is very hot, seawater may usefully be sprayed on the fish. On board large size vessels equipped with a main storage freezer and where some advanced processing of the tuna is planned, several crew members are normally paying careful attention to the fish, the optimum quality of which is normally making great difference in term of value. The nets are cleaned and the gillnets are carefully arranged again (floats and headrope on one side, leaded footrope on the other, buoys and buoyline in a specific park or rack), in general, on the aft part of the boat in preparation for the next setting.

Fishery Overview This fishing technique is used, among other, by the following fishing fleets: Sri Lanka, India, Philippines, India, Indonesia, China, Belize, Honduras, Japan, Panama, Rep. of Korea, Taiwan, Maldives, Belize, France, Netherlands Antilles, Seychelles, Spain, Italy. Drifting gillnets are used to catch different species of tunas in the South east Asia, Western and Central Indian, Western Mediterranean (Tirrenian, Ligurian, St. Sicily).

FAO Fisheries and Aquaculture Department Seasonality Tuna drifting gillnets is a seasonal fishing technique following the migration patterns of target species.

Issues

Discard The use of drifting gillnets on the high seas (specially in the western Pacific Ocean for tuna) was discontinued after 1992 because, in certain areas and under some circumstances, they may catch large amounts of marine mammals, sea turtles and, occasionally, sea birds. Regulation was taken prohibiting the use of drifting gillnets at large-scale/industrial level (which means kilometers of gillnets in one string); in the Northeast Atlantic, the use of drifting gillnets is authorized only until 2002 and with a length of the net limited to no more than 2.5 km . However, drifting gillnets are still widely used, and very popular, in many coastal and small to medium-scale fisheries in developing countries, particularly in Southeast Asia.

FAO Fisheries and Aquaculture Department