Present from Torres Strait to eastern Tasmania as far as 43°S, and from southwestern Australia at about 128°E to Northern Territory waters at about 136°E.

Stock structure: Yellowfin tuna are presumed to form separate stocks in each of the major oceans. Limited mixing may occur between the Pacific and Indian oceans through Indonesia, and there is probably some mixing between the major fisheries regions in the eastern Pacific and western Pacific oceans (Ref. 30313). Yellowfin tuna appear to form local groups off south-eastern Australia, and there is limited evidence of mixing with yellowfin tuna of other western Pacific areas (Ref. 30312). Stock structure of Western Australia yellowfin tuna has not been investigated.

Commercial fishery: Yellowfin tuna support substantial commercial fisheries in the warm waters of the eastern and western Pacific oceans and western Indian Ocean (Ref. 30310). Yellowfin tuna are commonly caught off south-eastern Australia where sea surface temperatures are between 18°C and 22°C.

Fishing with drifting longlines accounts for most of the commercial catch of yellowfin tuna in Australian waters.

As part of their global fishing operations, the Japanese fish for yellowfin tuna with longlines off eastern Australia, but further offshore and over more northerly waters than the Australian longline fishery. Japanese vessels are usually 200-300 t (40-45 m) in size. On average, each Japanese longliner spends 1 or 2 months in the Australian Fishing Zone during its 6-18 month fishing campaign. Some also fish off north-western Australia and in the vicinity of the Cocos-Keeling and Christmas islands.

The Japanese commenced longlining off eastern and western Australia during the early 1950s. However, since the declaration of the Australian Fishing Zone in 1979, Australian Government restrictions on access have modified Japanese fishing patterns in Australian waters. Now, fishing patterns in the Australian Fishing Zone are variable: some vessels fish off the east coast between 25°S and 34°S in July to October; others operate in more northerly waters between October and January. Most Japanese vessels leave the Australian Fishing Zone by January, having fished as far as north Queensland waters. A few remain there until February or March. In some years, during full moons in October-December, yellowfin tuna and bigeye tuna are caught by pole-and-line and handline in warm (>25°C) waters off north Queensland (Ref. 30309, 30314).

Yellowfin tuna caught by the Japanese are frozen and sold as ‘sashimi’ (raw fish) in Japan. They target adult yellowfin (30 kg average dressed weight), bigeye tuna, broadbill swordfish (Xiphias gladius) and striped marlin (Tetrapturus audax). Albacore (Thunnus alalunga), black marlin (Makaira indica) and blue marlin (M. mazara) are also taken. Off north-western Australia, Japanese longliners fish for yellowfin tuna, bigeye tuna and striped marlin during summer.

Australian fishers catch yellowfin tuna mainly off south-eastern Australia, where they have fished with longlines for tunas since the 1950s. The Australian longline fleet grew rapidly with the successful air-freighting of yellowfin tuna to Japan in 1984. Vessels range from 25 t to 150 t (10-28 m) in size. The fishery targets adult yellowfin tuna (25 kg average dressed weight) and bigeye tuna.

Broadbill swordfish and albacore are the main bycatch of the Australian longline fishery. The domestic longline season commences off southern Queensland and northern New South Wales in August and spreads southwards following the warm East Australian Current along the coast. Sporadic catches are reported from north-eastern Tasmania in February and March. Catches are reported from the far south coast of New South Wales as late as May or June. A few vessels occasionally longline for yellowfin tuna off north Queensland during October-January. In Western Australia, there is almost no fishing by Australians for yellowfin tuna.

The longlines consist of a main line and a series of branch lines with baited hooks. Longlines set by Australians are generally shorter than those used by the Japanese operating further offshore. Both Japanese and Australians target yellowfin tuna, setting lines to fish at 50-150 m depth. Deeper sets to 250 m - which target bigeye tuna - are occasionally made.

During the late 1980s, most yellowfin tuna caught by Australian longline fishers were sold fresh at sashimi markets in Japan. However, a few years before 1990, the Australian sashimi market has accounted for an increasing proportion of the catch and by 1990 almost half of the Australian yellowfin catch was sold at domestic markets.

The price for yellowfin tuna on sashimi markets is variable. Fish sold on the fresh-chilled sashimi market in Japan receive higher prices. Yellowfin tuna from waters south of 25°S are of particularly high quality and fetch much better prices than those caught in warmer waters.

Yellowfin tuna are also caught by other fishing methods in Australia. These tuna are a bycatch of Australian vessels using pole-and-line and purse seine to target skipjack tuna. Most of the yellowfin tuna caught by these methods are taken off southern New South Wales, and canned in Australia. Other fishing methods for this species include trolling, handlining and droplining.

The annual Australian yellowfin tuna catch of around 3000 t is dwarfed when compared with the catch taken in the tropical western Pacific. The South Pacific Commission (Ref. 30315) estimated that over 300,000 t of yellowfin tuna were caught in that region in 1990. Over 200,000 t of this were landed by purse seine, with longlining and poling accounting for most of the remainder.

Recreational fishery: Yellowfin tuna are prized by gamefishers in Australia and are the prime target of gamefishing on the south coast of New South Wales - 1 of the few locations where they can be caught from the shore. More commonly, though, these tuna are caught by trolling lures or baits. Baits include small skipjack tuna, pilchards and mackerel (Scombridae). Yellowfin tuna are also caught from drifting boats by anglers using dead or live bait such as nannygai or redfish (Centroberyx species) along with berley.

Anglers fish in the same areas as Australian longliners, but generally closer to shore. They take a wide size range of yellowfin tuna, but often tag and release those smaller than 20 kg. The Game Fishing Association of Australia’s record for yellowfin tuna up to 1993 was, 102 kg. Angler clubs in eastern Australia reported landing almost 2,887 yellowfin tuna in 1988-89, with a further 2,233 tagged and released (Ref. 30284).

Resource status: Longline catch rates of yellowfin tuna in western Pacific declined by about 50% between 1952 and 1982, then were fairly stable during the remainder of the 1980s. Preliminary assessment of the yellowfin tuna in the western Pacific based on a long time-series of longline data suggested a maximum sustainable yield for the longline fishery of 68,000-112,000 t in the area west of 180°E (Ref. 30313). However, since the mid 1980s, large-scale purse seining, targeting yellowfin tuna of a smaller average size, has grown to be the major fishing method in the region. Yellowfin tuna catches in the western Pacific exceeded 300,000 t by 1990 (Ref. 30315). Early 1990s analyses of tag-recapture results suggest that the purse seine catch of yellowfin tuna could be increased to 500,000 t without causing a significant decline in their abundance.

For many years, catches from the Australian Fishing Zone have varied around current levels, so are probably sustainable with the present fishing pattern and levels of effort. Links between yellowfin tuna in the eastern Australian Fishing Zone and those of the wider western Pacific Ocean are uncertain. As a result, the impact of the steadily expanding western Pacific yellowfin catches is also uncertain. Also Ref. 2334, 13465.