The Pacific bluefin tuna (Thunnus orientalis) is a species of tuna primarily found in the North Pacific, ranging from the East Asian coast to the western coast of North America. It is a notable resident of the marine ecosystem, primarily navigating the northern – and occasionally southern – Pacific Ocean. This species of tuna is widely recognized for its distinct physical attributes, incredible endurance, and significant value to the global seafood market.
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Characteristics
The Pacific bluefin tuna is a large fish species, with a maximum reported length of 3 metres and a maximum reported weight of 550 kg. Individuals longer than 2 metres are regularly seen.
The skin varies in shades from metallic blue to silvery white, providing ideal camouflage.
Their bodies are characterized by an elongated, torpedo-like appearance, with a sleek and streamlined body structure designed for fast, efficient movement. The bluefin is celebrated for its swiftness, as it can readily hit speeds of up to 75 kilometers per hour, making it one of the speediest occupants of the ocean.
Distribution and habitat
The Pacific bluefin tuna is chiefly found in the North Pacific, from the East Asian coast to the western coast of North America, but this is a migratory species and it is occasionally encountern further south than this.
While it is mainly a pelagic species inhabiting temperate waters, it also ventures into coastal regions and subtropical and tropical waters. The typical dept range for the Pacific bluefin tuna is from the surface to circa 200 metres below, but individuals have been recorded as deep down as 550 metres.
Diet
The Pacific bluefin tuna mostly eats small schooling fish and squids, but can also go for other things, including krill, crabs, and attached (sessile) animals.
Life and Breeding
Pacific bluefin tuna are migratory species that undertake vast trans-Pacific voyages. Young tunas often circulate around the eastern Pacific, particularly along the coasts of California and Mexico, before traveling across the ocean to mature in the seas surrounding Japan.
The Pacific bluefin tuna’s reproductive pattern involves migration. Adult bluefin tuna typically move to the Sea of Japan to spawn between the spring and summer months. Afterward, they embark on the long journey back to the eastern Pacific.
This species normaly reaches sexual maturity around the age of 5 and is then around 1.5 metres long and weighs around 60 kg. The larger the female is, the more eggs she can carry, and up to 25 million eggs have been found in really large specimens.
Spawning takes place from April to August, with the exact timing varying from one region to the next. In the southern range of its breeding area, such as the northwest Philippine Sea, breeding tends to happen early, e.g. April and May. In the Sea of Japan to the north, breeding takes place late in the season.
This is a warm blooded fish
Most fish species are ectothermic (“cold-blooded”) but tuna species and mackerel sharks are warm-blooded and can regulate their body temperature. To maintain the desired temperature, they rely on a system where heat in the warm vein blood is transferred to the colder arterial blood instead of being lost at the gills. Compared to other fish, these fishes lose much less heat through their gills.
A closer inspection reveals that the tunas have special near their muscles consisting of minute parallel veins and arteries that supply and drain the muscles. These organs are called retia mirabilia. When the warm blood in the veins moves towards the gills to pick up new oxygen, it comes near the cooler arterial blood and the heat is transferred.
Tunas in warm waters do not need to elevate their body temperature by more than a few degrees compared to their surroundings, while tunas in colder conditions can need to raise it by as much as 20 degrees C.
Sale and Consumption of Pacific Bluefin Tuna
The Pacific bluefin tuna is a prized catch in commercial and sport fishing. It is highly desired for its tender meat, particularly in Japanese cuisine where it’s the star ingredient in many sushi and sashimi dishes. Roughly 80% of the Pacific and Atlantic bluefin tunas that are consumed end up being eaten in Japan.
In early January 2019, a new record was set when a 278-kilogram Pacific bluefin caught off Oma in northern Japan sold for a staggering 333.6 million yen (3.1 million USD) in Tokyo’s renowned Tsukiji fish market. Tunas made available for the first time in a new year are considered good luck and therefore fetch an especially high price.
Environmental Impact and Conservation Status
The Pacific bluefin tuna, with its incredible characteristics and indispensable role in marine ecosystems, is a species deserving our attention and respect. The future of this remarkable creature, however, rests with our collective commitment to conservation and sustainable fishing practices.
Bluefin tuna is a crucial part of the aquatic ecosystem, helping maintain a balance among different species. This species is particularly significant due to its position at the top of the food chain. The Pacific bluefin consumes a substantial amount of smaller fish, cephalopods, and crustaceans, thus regulating these populations.
The Pacific bluefin tuna is currently classified as vulnerable by the International Union for Conservation of Nature (IUCN). As recently as 2011, it was listed by the IUCN as Least Concern. In 2014, it’s status was changed to Vulnerable, and it is now listed as Near threatened.
The situation is not all bleak, however. According to the 2022 stock assessments by the International Scientific Committee for Tuna and Tuna-Like Species in the North Pacific Ocean (ISC), the Pacific bluefin tuna population increased from a low point of about 2 percent of historic levels in 2010 to about 10 percent in 2020.
Various organizations worldwide, such as the World Wildlife Fund (WWF) and the Monterey Bay Aquarium’s Seafood Watch program, are taking critical steps towards protecting and conserving this unique species.
Note: It is important to keep in mind, when looking at older numbers, that the Atlantic bluefin tuna and the Pacific bluefin tuna have commonly been considered the same species in the past. It can therefore be difficult to find estimations regarding only the Pacific bluefin tuna.
Farming tuna
Japan is the leading researcher when it comes to tuna farming. As early as 1979, Kinki University (Kinki daigaku) successfully farmer already-hatched bluefin tuna, but it would take until 2002 before they found a way to breed them in captivity. In Japan, farm-raised tuna is now called Kindai tuna, after the university (Kinki daigaku).