It is the king of sushi, one of the most expensive fish in the world - and dwindling so rapidly that some fear it could vanish from restaurant menus within a generation.
Yet there is little alarm in Japan, the country that consumes about 80 per cent of the world’s bluefin tuna.
Japanese fisheries experts blame cosy ties between regulators and fishermen and a complacent media for failing to raise public awareness.
"Nobody really knows the bad state bluefin tuna is in," veteran sushi chef Kazuo Nagayama said from his snug, top-end sushi bar in Tokyo’s Shimbashi district, a popular area for after-work socialising.
"I don’t think it’ll disappear, but we might not be able to catch any. It’s obvious we need to set quotas."
Catching bluefin tuna, called "hon-maguro", is a lucrative business. A single full-grown specimen can sell for 2 million yen ($20,832) at Tokyo’s sprawling Tsukiji fish market. Japanese fishermen are vying with Korean, Taiwanese and Mexican counterparts for a piece of a $A900 million a year wholesale market.
Fish dealers at Tsukiji market say the number of bluefin sold at early morning auctions has fallen over the past 10 to 15 years, but most are confident the supply will never run out. Sushi bars and supermarkets still readily sell the fish, which is considered a special treat that families might splurge on once every month or two. There’s no government campaign to encourage people to rein in their appetites for the iconic Japanese food.
"I have seen some reports on TV about their numbers falling, but I really haven’t thought about cutting back on eating hon-maguro," said Sumire Baba, a Tokyo homemaker. "I guess I’m optimistic they’ll recover."
A scientific assessment released in January found that Pacific bluefin spawning stocks - a key measure of adults that can reproduce - have plummeted by about three-quarters over the past 15 years to match historic lows last seen in the early 1980s.
It estimated that the species has dwindled to just 3.6 per cent of its original population, and that more than 90 per cent of fish caught were juveniles between the ages of 0 and 3, before they reach reproductive maturity.
The report, compiled by the International Scientific Committee for Tuna and Tuna-like Species in the Northern Pacific and based on data through 2010, received only scant coverage in the Japanese press.
News reports earlier this year about the record 155.4 million yen ($A1.62 million) auction sale of a Pacific bluefin at the Tsukiji market focused mostly on the exorbitant price and the buyer - the owner of a sushi chain - with little context about the species’ falling numbers.
The drop follows similar plunges in the other two bluefin species, the Atlantic and the southern, which are now protected by catch quotas that experts say need to be applied to their Pacific cousins as well.
Without stricter caps, "there is a high likelihood that Pacific bluefin will become less available to Japanese consumers," said Masayuki Komatsu, a former senior Fisheries Agency official. Japan faces two choices, he said: immediately impose catch quotas or "stop eating the bluefin to protect it".
Overfishing of the Atlantic bluefin, much of it shipped to Japan, got so bad that an export ban was proposed in 2010 at a meeting of the 175-nation Convention on International Trade in Endangered Species (CITES). The proposal was rejected, and Atlantic bluefin stocks recovered slightly last year after quotas were imposed, although environmental groups say the population remains fragile.
Toshio Katsukawa, a fisheries professor at Mie University in western Japan, says the fishing industry has been allowed to pursue indiscriminate fishing for years.
"This is undermining Japan’s own national interests," he said. "We have an international responsibility in this matter. It’s a problem if we are not able to responsibly catch and consume these fish."
That may have been a valid criticism in the past, acknowledged Masanori Miyahara, the deputy director-general of the Japan Fisheries Agency. But over the past five or six years "our policy has changed," he said in an interview in his Tokyo office. "Now we are in the driver’s seat."
"Previously, there was almost no control over the bluefin catch because so many fishermen were catching them. The JFA just gave up," Miyahara said. "But now we are in a position of control. We are serious about fishing management."
He noted that limits imposed in 2011 on domestic fishermen using large, encircling "purse seine" nets - which scoop up vast amounts of fish, including many young ones - during the summer spawning season in the Sea of Japan have reduced the catch of juveniles by more than a quarter.
Japan also has joined 2011 "effort limits" - such as limiting the number of vessels - called for by the Western and Central Pacific Fisheries Commission, the regional fisheries body that monitors the western two-thirds of the Pacific Ocean. The commission will meet in Tokyo in September to consider whether to strengthen catch restrictions.
Japan also has placed caps on the number of tuna farms, which take young tuna caught at sea and raise them in coastal waters, and is registering its 13,000 independent fishermen to better monitor their catch, Miyahara said.
But conservation groups say the measures are full of loopholes and not well enforced, while Japanese fishermen complain that South Korean boats are not similarly constrained.
While Japanese consumers are very sensitive about food safety and quality, awareness about resource management is still not very prevalent. Major retailer Aeon Co has a line-up of 50 products with a special blue label from the Marine Stewardship Council, which certifies sustainable marine foods.
However, MSC-labelled products account for only three per cent of Aeon’s total fish sales.
"Eating fish is a fundamental part of Japanese culture," said Kozo Ishii, the program director for MSC in Japan. "That fish is readily available is taken for granted."
A handful of US and European sushi restaurants have removed bluefin from their menus, but Nagayama, the sushi chef, hasn’t heard of that happening in Japan.
He tries to minimise the amount of the fish he uses, but says he needs to have it on hand because customers request it. A single piece of pink "o-toro" fatty tuna goes for Y2000 yen ($A21) at his shop, although customers visiting "conveyor belt" sushi shops can grab much lower quality bluefin for 100 yen, or just over a dollar.
"We’re a top-end sushi bar, so we need to have it," said the 71-year-old sushi chef, who has written three books about fish. "If we don’t, we can’t really do business."