Western and Central Pacific Ocean

In the Western and Central Pacific Ocean (WCPO), purse seiners take the majority of the yellowfin tuna catch (over 60% in recent years); the longline fleet takes about 15% and most of the remainder is taken by the domestic fisheries of Philippines and Indonesia that use a variety of gears. More than half of the total yellowfin catch from the WCPO comes from within the Exclusive Economic Zones (EEZs) of the eight Pacific Island countries that are the members of the Parties to the Nauru Agreement (PNA) (Federated States of Micronesia, Kiribati, Marshall Islands, Nauru, Palau, Papua New Guinea, Solomon Islands and Tuvalu).

Due to the large increase in numbers and size of purse-seine fishing vessels targeting skipjack tuna since the late 1970s, the average annual yellowfin tuna catch in the Western and Central Pacific Convention Area increased from 100,000 tonnes in 1970 to around 500,000 tonnes in recent years. Because small yellowfin and bigeye tuna are difficult to distinguish, yellowfin tuna may not always be reported accurately in catches dominated by skipjack tuna. Reported catches may need to be adjusted by factors up to 15-20% to correct for sampling and reporting bias.

In the WCPO, the number and average size of purse-seine vessels targeting skipjack, yellowfin and bigeye tuna have been increasing. The current industrial purse-seine fleets (nearly 300 vessels) come from the 3 main groups of countries: 1) the historically strong tuna fishing nations, i.e., Japan, Republic of Korea, Taiwan and United States of America; 2) Pacific Island countries that either have their own fleets or register foreign-owned vessels under their flags (Federated States of Micronesia, Kiribati, Marshall Islands, Papua New Guinea, Solomon Islands, Tuvalu and Vanuatu); and 3) newer tuna fishing nations (China, Ecuador, El Salvador, New Zealand and Spain).

In the WCPO, yellowfin tuna caught in purse-seine sets on free schools are often adult fish (> 100 cm fork length - FL), whereas smaller yellowfin tuna are generally caught in sets on FADs and logs. In the domestic surface fisheries of the Philippines and Indonesia, the catch includes many small yellowfin tuna in the size range of 20-50 cm FL. The association of tuna with floating or anchored devices has become a prime issue in tuna fisheries management, most notably for the need to control the catches of bigeye tuna which are an order of magnitude higher than those of bigeye tuna from unassociated sets.

The longline catch of yellowfin tuna is comprised almost entirely of adult fish (>100 cm FL). The catch of adult yellowfin tuna by purse-seine (by weight) is usually higher than that of the longline adult yellowfin tuna catch.

Longline fishing for yellowfin tuna is carried out by 3-6,000 vessels, from China, Federated States of Micronesia, Japan, Republic of Korea, Indonesia, Papua New Guinea, Philippines, Solomon Islands, Taiwan, Vanuatu, and Vietnam. However, because the catch supplies the high-value sashimi tuna market, the value of yellowfin tuna from longline fishing is similar to that of the larger volume from purse-seine fishing. Pole and line fishing, largely in the western part of the WCPO, accounts for about 4% of the total yellowfin catch.

In the WCPO, artisanal gears for yellowfin tuna include handline, small coastal longline and troll. The domestic fleets are diverse and multipurpose, from artisanal and traditional coastal fishery fleets especially in Indonesia and Philippines, and including composite industrial and small-scale fisheries. In Indonesia, Papua New Guinea, Philippines and Vietnam, artisanal fleets of small vessels operate around anchored FADs using handlines and small vertical longline gears. The commercial handline fleets target large yellowfin tuna which comprise the majority of their catch (> 90%).

Collecting accurate catch statistics from fleets using composite fishing gears (FADs and small-scale gear) is very difficult due to the diverse and unregulated nature and the rate of expansion. The Western and Central Pacific Fisheries Commission (WCPFC) are making concerted efforts to collect such data with considerable progress in recent years.

Indian Ocean

In the Indian Ocean (IO), the yellowfin tuna catch is a high proportion (44%) of the total IO tuna catch. IO yellowfin tuna are caught by a wide variety of gears and scales of operations. The long-dominant fishing methods for yellowfin tuna, purse seine (currently just over a third of the catch) and longline (one fifth), are declining in relative importance. Artisanal and semi-industrial gears, especially gill nets (one sixth of yellowfin tuna catch) and miscellaneous types (one fifth) are increasing rapidly as more countries in the IO target yellowfin tuna. Pole and line, one of the minor gear types, takes about 5% of the catch.

In the most productive Western Indian Ocean areas, pirate activity off Somalia, Kenya, Tanzania and Seychelles has depressed longline fishing and to some extent purse seine fishing for several years, but this disruption has now largely ended.

In tropical areas, both surface and longline fisheries occur year-round, but in the higher (subtropical/temperate) latitudes, the longline fisheries are seasonal.

The main fleets catching yellowfin tuna in the IO are from Spain (purse seine), France (purse seine), Sri Lanka (gillnet, longline, pole and line, troll, handline and other various artisanal gears), Maldives (pole and line and, increasingly in recent years, handline), Indonesia (purse seine, longline, handline, gill net, troll, pole and line, liftnet and various other artisanal gears), Iran (gill net, purse seine), Republic of Korea (purse seine, longline), Seychelles (purse seine, longline), Yemen (handline and troll), India (many gears), Comoros (hand and troll lines), and other countries with longline fleets (Japan, Taiwan, China, Philippines, South Africa).

Most of the yellowfin tuna purse-seine catch is taken in the Western Indian Ocean, around Seychelles and off the coast of Somalia and in the Mozambique Channel. Vessels of the European Union distant water fleet (France and Spain) take most of the catch and land the fish in the Seychelles.

In the IO, purse seiners take both small and adult fish (40 – 140 cm FL). Fishing uses two different modes: fishing on floating objects (FADs) that yields large numbers of skipjack tuna along with juvenile yellowfin and bigeye tunas, and fishing on free swimming schools that catches larger yellowfin tuna, with or without other tuna species. The majority of the purse seine catches of yellowfin are sold for canning with a small but increasing amount of yellowfin tuna is preserved deep-frozen on board and sold for the sashimi markets.

The IO longline fishery takes predominately large fish (80 - 160 cm FL), except for catches by Taiwanese longliners (and gillnetters from IO countries) in the Arabian Sea, where smaller fish (60– 100 cm FL), dominate catches. In tropical waters, yellowfin and bigeye tuna are the main longline target species.

While in the past the majority of the yellowfin tuna was caught by deep-freezing longliners for the sashimi market, in recent years the majority of the catches of yellowfin tuna have come from the fresh-tuna longline fleets of Indonesia and Taiwan, which export the catch chilled for the sashimi market or sell it to the fresh market.

In the IO, the artisanal and semi-industrial fisheries take a substantial and increasing component (20-30%) of the yellowfin tuna catch. Among these fisheries, gillnets are the most common method taking much (about 80,000 tonnes) of the juvenile or pre-adult yellowfin tuna. Other gears include pole-and-line, which also takes juvenile yellowfin tuna, and troll and handline. Large catches are landed by fleets from Sri Lanka (gillnet and longline combination), Pakistan and Iran (gillnet), the Maldives (pole-and-line, handline), and Indonesia (longline and various artisanal gears) and India (longline and trolling). A substantial amount of juvenile yellowfin tuna is caught in association with anchored-FADs, especially in Indonesia and, to a lesser extent, Maldives.

The Maldives catch of yellowfin tuna is about 23,000 tonnes annually, caught by two gears: pole-and-line and handline. Pole-and-line fishing catches juveniles.