The Pacific bluefin tuna (Thunnus orientalis) is a predatory species of tuna found widely in the northern Pacific Ocean, but it is migratory and also recorded as a visitor to the south Pacific.
In the past it was often included in T. thynnus, the 'combined' species then known as the northern bluefin tuna (when treated as separate, T. thynnus is called the Atlantic bluefin tuna). It may reach as much as 3 m (9.8 ft) in length and 450 kg (990 lb) in weight.
Like the closely related Atlantic bluefin and southern bluefin, the Pacific bluefin is a commercially valuable species and several thousand tonnes are caught each year, making it overfished. It is considered threatened by the IUCN and PEW. Monterey Bay Aquarium's Seafood Watch program have placed all bluefin tunas on the "Avoid" list and they are also placed on the "Red List" by Greenpeace and the Blue Ocean Institute.
The Pacific bluefin tuna is primarily found in the North Pacific, ranging from the East Asian coast to the western coast of North America. It is mainly a pelagic species found in temperate oceans, but it also ranges into the tropics and more coastal regions. It typically occurs from the surface to 200 m (660 ft), but has been recorded as deep as 550 m (1,800 ft).
It spawns in the northwestern Philippine Sea (e.g., off Honshu, Okinawa and Taiwan) and in the Sea of Japan. Some of these migrate to the East Pacific and return to the spawning grounds after a few years. It has been recorded more locally as a visitor to the Southern Hemisphere, including off Australia, New Zealand, the Gulf of Papua and French Polynesia.
The species is considered to consist of only one stock.
Pacific bluefin tunas reach maturity at about 5 years of age, the generation length is estimated at 7–9 years and based on two separate sources the longevity is 15 years or 26 years. At maturity it is about 1.5 m (4 ft 11 in) long and weighs about 60 kg (130 lb). Individuals that are 2 m (6 ft 7 in) long are regularly seen, and the maximum reported is 3 m (9.8 ft) in length and 450 kg (990 lb) in weight. Elsewhere, a mass of up to 550 kg (1,210 lb) has been reported for the species. According to the International Game Fish Association, the all-tackle game fish record was a 411.6 kg (907 lb) individual (Donna Pascoe) caught on 19 February 2014 onboard charter boat Gladiator during the National Tournament.
Spawning occurs from April to August, but the exact timing depends on the region: Early in the northwest Philippine Sea (the southern part of its breeding range) and late in the Sea of Japan (the northern part of its breeding range). Large females can carry more eggs than small ones, and between 5 million and 25 million eggs have been reported.
Pacific bluefins eat various small schooling squids and fishes, but have also been recorded taking sessile animals, pelagic red crabs and krill.
Unlike the other bluefins (Atlantic and southern), the Pacific bluefin tuna was not considered threatened initially, resulting in a Least Concern rating in 2011. In 2014, it was found to be threatened and the status was changed to Vulnerable. Overfishing is occurring in the Pacific bluefin, but overall the stock was not yet believed to be in an overfished condition in 2011.
According to stock assessments completed in 2011, 2014 and 2016 by the International Scientific Committee for Tuna and Tuna-Like Species in the North Pacific Ocean (ISC), the present-day population is at just 2.6 percent of its historic levels. The overall fishing mortality rate for this species remains up to three times higher than is sustainable.
In 2010, it was estimated that the complete spawning biomass was 40–60% of the historically observed spawning biomass. In 2000–2004, between 16,000 tonnes and 29,000 tonnes were caught per year.
Its wide range and migratory behavior lead to some problems, since fisheries in the species are managed by several different Regional Fisheries Management Organisations that sometimes give conflicting advice. The IUCN have recommended that the responsibility be moved to a single organisation. Other recommendations include a substantial reduction of fishing of this species, especially juveniles. As much as 90% of the caught Pacific bluefins are juveniles.
Monterey Bay Aquarium's Seafood Watch program have placed all bluefin tunas on the "Avoid" list, and they are also placed on the "Red List" by both Greenpeace and the Blue Ocean Institute.
