Japan Has Too Much Bluefin Tuna—and Fishermen Must Throw It Back

A net full of treasure, and a decision to open it

In May, set-net fisherman Tadasuke Nakamura found hundreds of Pacific bluefin tuna packed into a net off Hakodate, Hokkaido. It looked like the haul every fishing community hopes to see. Nakamura let many of the fish go.

The choice was economic as well as legal. Japan’s bluefin catch is limited by size class and allocated among fisheries and prefectures. Landing the spring bonanza could exhaust the operation’s share before colder months, when the tuna carry more fat and command higher prices. A fish in the net was valuable; the same fish released alive preserved the chance to fish later.

The pattern was not confined to Hokkaido. In Fukui, fisherman Toshiharu Uratani said his operation used its half-year allowance for large tuna in the first three months. Fisheries Agency data cited by Reuters showed April coastal landings of tuna at least 30 kilograms were almost double the previous April.

Sado released more tuna than it landed

Off Sado Island in Niigata Prefecture, crews estimated by late May that they had released more than 500 tonnes of bluefin. The region had already consumed about 90% of its allocation during what fishermen described as an extraordinary spring run. Captain Masaru Yamamoto of the Utsukaifu fishing cooperative told FNN that recent releases exceeded landings.

A set net is not a hook baited for one species. A leader net intercepts fish moving along the coast and guides them into chambers. The gear waits for the ocean to arrive. It may contain yellowtail, sea bream, pufferfish, squid and tuna at the same time. If a mass of bluefin must be released, crews can have to lower or open part of the net; commercially intended fish escape with it. Large tuna can also damage the gear.

Shizuoka showed how quickly the constraint can arrive. The prefecture’s set-net sector reached about 95% of its large-tuna allocation less than three weeks after its April management year began, prompting a halt. These are vivid regional events, but they must not be mistaken for a census of the Pacific. They show that tuna availability and quota capacity were badly mismatched at particular coasts and times.

“Throw it back” means a live release—when it works

The headline can sound as if crews dump dead tuna. The intended practice is the opposite: open the net while the fish are alive and avoid handling. A tuna released from a crowded net is not automatically a survivor, however. Stress, abrasion, crowding, water temperature, time in the gear and the release method all matter. Released biomass should not be casually equated with saved biomass.

Japanese researchers and net makers have developed an Emergency Release Window, or ER window, that can be opened in the fish chamber. A selection panel may allow smaller tuna through while retaining larger fish. Trials reported by Tokyo University of Marine Science and Technology found survival above 80% for small bluefin released without being scooped or touched. In the same work, most fish handled with large or water-filled dip nets died.

That result explains the practical priority: identify tuna early, preserve swimming space and release before hauling compresses the school. Sonar and cameras can warn crews what has entered; modified chambers, submerged sections and powered winches can create an escape route. But a trial on small fish is not a universal mortality estimate for every mass release in 2026. Independent monitoring of post-release survival remains essential.

One fish, two weight classes, many ledgers

Pacific bluefin in the WCPFC area are managed in two categories: under 30 kg and 30 kg or more. The division is biological policy, not a culinary grade. Fishing a young animal removes not only that fish but its possibility of reaching the spawning population. The 2024 assessment credited much of the recovery to sustained reductions in fishing mortality on ages zero to three.

For 2025 and 2026, the WCPFC measure increased the western and central Pacific limit by 10% for small fish and 50% for large fish. Japan’s resulting shares are 4,407 tonnes of small fish and 8,421 tonnes of large fish. Those numbers are then distributed through domestic management: minister-managed fisheries, prefectural coastal fisheries, national reserve and transfers. Ministerial categories generally run January through December; prefectural categories run April through the following March.

How the “black diamond” reached its low point

Pacific bluefin, Thunnus orientalis, are born in the western Pacific. Most remain there, while some juveniles cross to the eastern Pacific, feed off North America for one to four years and return west to spawn. They mature at roughly five years, can live to about 26, and may reach three meters and 450 kilograms. That combination—long travel, late maturity and high value—makes national management alone inadequate.

Bluefin have been part of Japanese coastal fisheries for centuries, but twentieth-century refrigeration, aircraft, long-distance transport, purse seines, sonar and the global sushi market increased the speed and reach of harvest. Fishing pressure fell heavily on young fish before they reproduced. The assessment record shows spawning biomass collapsing to about 2% of the modeled unfished level in 2009–10, roughly 12,000 tonnes in 2010.

“Unfished biomass” is a model benchmark, not a claim that exactly that quantity once swam in a pristine ocean. But the direction was unmistakable. In 2016 the spawning stock was estimated at only about 21,000 tonnes, or 3.3% of the benchmark. Scientists warned that a stock capable of crossing an ocean had become dangerously small.

2015: Japan accepted a hard brake on juveniles

WCPFC members agreed in 2014 to constrain western Pacific catches from 2015. The core rule cut catches of fish under 30 kg to half the 2002–04 average and held large-fish catches around the earlier baseline. Japan’s initial limits were 4,007 tonnes for small fish and 4,882 tonnes for large fish. Offshore fisheries were divided by gear; coastal fisheries were first managed in six blocks and later mainly by prefecture.

The system was initially a domestic voluntary program implementing an international commitment. In 2018 Japan placed Pacific bluefin under the statutory total allowable catch system—January for offshore sectors and July for coastal sectors in that transition year. What had been restraint became enforceable quota accounting.

The rebuilding plan set two waypoints. The first was 6.3% of unfished spawning biomass, corresponding to the historical median used at the time. The second was 20%, to be reached by 2034. As catches of juveniles fell and stronger year classes matured, the stock crossed the first target and then surpassed the second in 2021—about a decade early.

A twelvefold recovery, with no permission to forget

The ISC’s 2024 assessment estimated 2022 spawning biomass at about 144,000 tonnes, 23.2% of the unfished benchmark and roughly twelve times the 2010 trough. NOAA called it the largest biomass recorded in the assessment series. The WCPFC summarizes the stock as neither overfished nor undergoing overfishing under the applicable reference points.

This is an unusual conservation story because the sacrifice is visible on both sides. Earlier restrictions hurt fishing communities, especially those encountering tuna unintentionally. Yet those restrictions are a central reason so many large fish now reach Japanese coasts. The quota paradox is not evidence that management failed. It is evidence that successful rebuilding has created a new management problem.

Nor does recovery mean invulnerability. The estimate has uncertainty. Recruitment can vary. Catch outside management assumptions, including unrecorded discard mortality, could alter projections. The stock crosses two regional commissions and many jurisdictions. A valuable, slow-maturing predator can be driven down again faster than international policy can be rebuilt.

Why 2026 feels different from the assessment year

The latest full assessment describes the stock through 2022. Fishermen are describing their nets in 2026. A scientific assessment necessarily lags, while daily catch data arrive immediately. The mismatch does not make either perspective false.

Three processes may be overlapping. First, there are simply more adult bluefin than at the 2010 low. Second, the age structure has changed: protecting juveniles allows more fish to cross the 30 kg boundary. Third, currents, prey and temperature can change where and when the stock becomes available to coastal gear. Reuters reported expert views that changing migration patterns linked partly to ocean warming may be contributing to the 2026 concentration.

That climate explanation remains a hypothesis for this particular surge, not an attribution result. A tuna at Hakodate does not prove warming put it there. Tagging, size composition, temperature, current and prey data are needed to separate abundance from redistribution. Management needs both kinds of information: the slow, stock-wide assessment and the fast map of where unavoidable encounters are occurring.

The July talks failed to turn recovery into a rule

Japan entered the July 8–11 joint WCPFC–IATTC working group in Nagasaki supporting a management procedure that would use an agreed formula rather than renegotiate every quota increase. Under the option Japan endorsed, the western and central Pacific large-fish allowance would rise 25% for 2027 while the small-fish allowance would fall 6%. The reduction for smaller fish was meant to preserve the rebuilding gains while shifting harvest toward older tuna.

The group did not reach consensus. The official chair’s summary records disputes over the long-term harvest control rule, how fishing impact should be balanced between western and eastern Pacific fleets, conversion between small- and large-fish quotas, carryovers and sport fishing. Japan said one member insisted on moving the modeled west–east impact balance from the current 82:18 to 75:25; Japanese officials and local reporting identified Mexico. Mexico and the United States argued for a more equitable east–west balance and favored a different rule.

This distinction matters: the meeting did not conclude that a 25% increase was biologically impossible. It failed to agree on the management procedure and on how its opportunities and risks would be distributed. Without consensus, the chairs warned, current measures could remain in place. Further commission decisions are due in the annual process later in 2026.

Fairness inside Japan is as difficult as fairness across the Pacific

A quota can be biologically sound at ocean scale and still distribute pain unevenly. Purse-seine vessels target schools and can plan effort around an allocation. Set-net crews are passive recipients of whatever follows the coast. A prefecture with a sudden run can be forced to release fish while another allocation remains unused elsewhere. A spring landing can crowd out a higher-value winter fish.

Japan has reserves, transfers and quota-conversion rules to soften those edges. The Fisheries Agency said the 2025 large-fish increase was allocated with special consideration for coastal operators carrying heavy release burdens. Individual quotas were introduced for major purse-seine and tuna fisheries in 2022 and for some drift-net fisheries in 2023. These tools make responsibility clearer, but they do not make a fixed net selective.

A durable system needs transparent in-season transfers, rapid reporting, an emergency reserve for unavoidable coastal bycatch, and allocation rules that reward low mortality rather than merely recorded landings. It should also disclose release quantity and survival by method. Otherwise, a tonne opened from a net can disappear from both the market ledger and the conservation ledger.

What a smarter response would look like

The WCPFC’s management strategy evaluation shows why no single formula satisfies everyone. Rules that produce higher catch may bring more frequent quota changes or less biomass buffer; conservative rules protect against uncertainty but prolong releases and lost income. A ±25% cap smooths sudden changes but can also make policy slow to follow a rapidly growing stock.

The answer is not to discard science when nets fill, or to ignore fishermen until the next assessment. It is adaptive management: pre-agreed rules, current data, selective technology, accountable transfers and a margin for uncertainty. Recovery should make management more sophisticated, not more complacent.

From collapse to crowding: the bluefin timeline

There are not “too many” tuna. There are too few flexible rules

The 2026 images invert a decade of conservation messaging: a fisherman looks at a net thick with bluefin and calls the prized fish an obstacle. It would be easy to conclude that the quota has become absurd. It would be equally easy to say the release is simply the necessary price of conservation. Both answers are incomplete.

Pacific bluefin really did recover. Coastal crews really are absorbing costs that an annual, fragmented allocation system handles poorly. Climate and migration may be redistributing encounters. Release technology can reduce harm but cannot make all discarded opportunity disappear. International science can set a safe envelope, but politics decides how it is divided.

The lesson of the 2010 low is not that quotas must never rise. It is that fishing opportunity should rise through rules capable of falling again. The lesson of Sado’s 500-tonne release is not that every fish should be landed. It is that management must count unavoidable encounters, survival, mixed catches and seasonal value—not only tuna carried across the dock.

Opening the net can be an act of stewardship. Being forced to open it repeatedly because policy cannot move quota in time is a design failure. Japan’s bluefin boom is therefore both a conservation victory and a warning: saving a stock is only the first half of sustainable fishing. The second is learning how to share its return.