Japan’s Fisheries Assessments
Reveal Two Different Seas

Japan did not publish one fisheries verdict on September 2. It published ten different stories about ten different biological populations—and the sharpest contrast is within a single species. In the Pacific stock of Japanese sardine, 2025 spawning biomass fell to 72% of the level associated with maximum sustainable yield while fishing pressure rose to 4.43 times Fmsy. In the Tsushima Current stock, spawning biomass was above its MSY target and fishing pressure was just 37% of Fmsy.

That divergence is the essential lesson in the Fisheries Agency’s latest release. The assessment covers eight species but ten stocks: Japanese jack mackerel and Japanese sardine are each split into two major stocks, alongside Pacific Japanese anchovy, red seabream in the western Sea of Japan and East China Sea, Pacific splendid alfonsino, Pacific round herring, maruaji in the western Sea of Japan and East China Sea, and a group of scads in the East China Sea. They are part of a national assessment program that now covers 192 species.

Why “ten stocks” matters more than “eight species”

Fisheries management works with biological populations, not supermarket labels. The Fisheries Agency explicitly notes that animals of the same species can have different spawning grounds, distributions and migration routes. That is why Japanese jack mackerel and Japanese sardine are assessed separately in Pacific and Tsushima Current units.

The sardine numbers make the principle concrete. The Pacific stock had 1.035 million tonnes of spawning biomass in 2025 against an SBmsy target of 1.432 million tonnes. Catch was 911,000 tonnes, while the model’s MSY is 470,000 tonnes. The Tsushima Current stock, by contrast, had 1.149 million tonnes of spawning biomass against a target of 1.089 million tonnes, with 149,000 tonnes caught. A national statement such as “Japan’s sardines are healthy” or “Japan’s sardines are depleted” would erase the most important information.

The Pacific sardine number that changes the conversation

The Pacific Japanese sardine assessment is difficult to dismiss as routine annual noise. Catch in 2025 reached 911,000 tonnes. The model’s MSY is 470,000 tonnes. A one-year catch above MSY is not, by itself, proof of overfishing—MSY is a long-run equilibrium concept and annual sustainable catches vary with recruitment and age structure. But the Kobe plot combines that catch with two more troubling signals.

Spawning biomass was 72% of SBmsy, and fishing pressure was 4.43 times Fmsy. The assessment says the stock expanded after 2010 and rose above SBmsy from 2019, but has recently turned downward as fishing pressure increased. Under the reference harvest scenario, the 2027 ABC is 162,000 tonnes and projected spawning biomass is 494,000 tonnes. The probability of being above the target by 2036 is 30%. Under a reference case that continues current fishing pressure, the probability is zero.

Those projections are not predictions of what regulators will actually permit. They are a way of showing the biological consequences of different fishing-intensity choices. The distance between 911,000 tonnes caught in 2025 and the 162,000-tonne 2027 ABC under the modeled scenario is precisely why managers, fleets and coastal communities will scrutinize the next policy steps.

The Tsushima sardine stock tells the opposite story

The Tsushima Current stock sat on the other side of both reference points in 2025. Spawning biomass was 1.149 million tonnes, 1.05 times SBmsy, while fishing pressure was 0.37 times Fmsy. The standardized spawning index jumped sharply in 2025 and purse-seine CPUE in Nagasaki remained high.

Under the assessment’s beta=0.8 scenario, the 2027 ABC is 527,000 tonnes, with projected spawning biomass of 1.579 million tonnes and a 57% probability of remaining above the target in 2036. That does not mean fleets are being told to harvest 527,000 tonnes. It means the stock’s modeled biological capacity is currently very different from that of its Pacific counterpart.

Anchovy is recovering, but recruitment still deserves attention

The Pacific Japanese anchovy stock is another case where a favorable headline needs context. Biomass in 2025 was estimated at 377,000 tonnes and spawning biomass at 165,000 tonnes. The latter was 1.47 times SBmsy, while fishing pressure was just 0.25 times Fmsy. Biomass and spawning biomass have increased since 2019.

Yet the research-vessel recruitment index has remained low since 2015, aside from relatively strong readings in 2021 and 2024. The assessment’s 2027 ABC is 112,000 tonnes. Managers therefore have to track not only how many adult fish are present now, but whether enough young fish are entering the population to sustain that abundance.

Japanese jack mackerel: both stocks are still short of the biomass target

The Pacific Japanese jack mackerel stock was estimated at 64,000 tonnes of total biomass in 2025, up from 36,000 tonnes in 2021. Spawning biomass, however, was only 25,000 tonnes—48% of the 52,000-tonne SBmsy target. Fishing pressure was 1.12 times Fmsy. The assessment’s 2027 ABC is 26,000 tonnes, with a 55% probability of exceeding the target in 2036 under the beta=0.9 scenario.

The Tsushima Current stock spans the East China Sea into the Sea of Japan and is assessed using Japanese and Korean catches. Combined catch was 80,000 tonnes in 2025, total biomass 304,000 tonnes and spawning biomass 158,000 tonnes. That spawning biomass was 58% of the 273,000-tonne target. Fishing pressure, however, had fallen to 65% of Fmsy. The 2027 ABC is 142,000 tonnes.

Both stocks are below their spawning-biomass targets, but the fishing-pressure signal is different. That is exactly the kind of nuance lost when “mackerel” is used casually to describe the release.

Round herring is the quiet red flag

The biggest species in tonnage tends to dominate the news, but Pacific round herring carries another strong warning. Catch peaked at 49,000 tonnes in 2015 and fell to 21,000 tonnes in 2025. Its resource index has declined since 2016 and stood at 0.86 in 2025.

This stock uses a different assessment framework, translating a set of abundance indicators into a percentile-like resource level. The 2025 level was 28.7%, well below both the proposed 80% target and proposed 56% limit. Both the basic rule and a fluctuation-smoothing rule produce a 2027 ABC estimate of 17,000 tonnes.

The word proposed is essential. Several stocks in this release—including round herring, splendid alfonsino and the data-limited scad stocks—carry reference points or harvest rules presented as proposals agreed or developed through research meetings. They should not be reported as already-final legal limits.

Red seabream shows how stock enhancement complicates the math

The western Sea of Japan and East China Sea red-seabream assessment is unusual because Japan’s long history of hatchery releases is built into its projection. Spawning biomass in 2025 was 13,100 tonnes. Rather than simply using the full SBmsy of 39,300 tonnes, the assessment applies a provisional reference point—SB84%msy of 13,100 tonnes—linked to the 1-to-6-year-old portion of the stock.

The forecast then adds hatchery-derived recruitment to natural reproduction. It assumes the 2021–2025 average of 320,000 hatchery-origin recruits per year continues. Under the beta=1.0 scenario, the 2027 average catch is 5,560 tonnes and the probability of exceeding the provisional target in 2035 is 45%; the assessment says that probability rises above 50% when beta is 0.99 or lower.

The point is not that stocking solves stock management. It is that a forecast can only be understood if its assumptions about human intervention are made explicit. Japan’s red-seabream program is a reminder that “wild stock” and “fishery production” are not always cleanly separable categories.

Splendid alfonsino: when oceanography changes catchability

Pacific splendid alfonsino had 29,700 tonnes of spawning biomass in 2025, 1.22 times the proposed SBmsy target, and fishing pressure at 0.66 times Fmsy. On those measures the stock appears comparatively strong. But the report spends unusual attention on the Kuroshio.

From 2017 through 2025, the Kuroshio Large Meander altered fishing conditions around the Kanto coast and Izu Islands. Standardized CPUE—which attempts to strip out environmental effects on catchability—often sat above raw CPUE during the meander. After the meander ended in April 2025, that relationship changed in some districts. In plain terms: if currents make fish easier or harder for boats to encounter, catch per unit effort can change even when the underlying stock does not change by the same amount.

This is the frontier of modern stock assessment. Climate and ocean variability do not replace fishing pressure as a management issue; they make it harder to measure the biological signal cleanly.

When age-structured MSY models are not possible

Japan does not have the same quality of age, recruitment and biomass data for every fishery. For maruaji and the East China Sea muroaji/scad group, the 2026 assessment applies what the Fisheries Agency calls “Rule 2,” using catch and standardized CPUE rather than a full age-structured MSY model.

Maruaji was at an 82.9% resource level in 2025, slightly above the proposed 80% target, producing a 2027 ABC estimate of 3,811 tonnes. The muroaji/scad group was at 73.3%, below the proposed 80% target but above the proposed 56% limit, producing a 3,374-tonne estimate.

This is not a lesser form of science so much as a different response to uncertainty. The mistake would be to print a Rule 2 percentage next to an SB/SBmsy ratio and pretend they measure exactly the same thing. They do not.

From the 1997 TAC system to an MSY-centered Fisheries Act

Japan’s current framework has a long institutional history. After ratifying the United Nations Convention on the Law of the Sea, Japan enacted its former marine-resource management law in 1996 and began the TAC system in January 1997. The original designated species included saury, Alaska pollock, Japanese jack mackerel, Japanese sardine, mackerels and snow crab; Japanese flying squid was added in 1998.

The deeper shift came with the 2018 overhaul of the Fisheries Act, implemented in December 2020. The new framework places scientific stock assessment at the center of management, sets targets around the stock level capable of producing MSY, and uses TAC management as the basic quantitative tool for designated resources. Kobe plots—spawning biomass relative to SBmsy on one axis, fishing pressure relative to Fmsy on the other—became a much more direct language for asking whether a stock is where managers want it to be.

At the same time, Japan radically expanded what it assesses. The national program covered 50 species in FY2018, 67 in FY2019, 119 in FY2020 and 192 by FY2021. The current system is therefore not only about refining advice for the biggest offshore fisheries. It is an attempt to put a much broader slice of coastal and regional fisheries inside a common scientific framework.

Sardine history is a warning against straight-line thinking

Japanese sardine has repeatedly shown that pelagic stocks can transform on scales larger than ordinary management cycles. The Pacific stock became enormous in the 1980s and then collapsed after recruitment deteriorated around the late 1980s and early 1990s. Fisheries research has long connected those changes with broad atmosphere-ocean ecosystem shifts as well as fishing.

The 2026 assessment still carries that history inside its model. For the Pacific stock it distinguishes a high-recruitment regime in 1976–1987 from a normal-recruitment regime beginning in 1988; current reference points and projections are based on the latter. The stock is therefore not assumed to reproduce as efficiently as it did during the extraordinary sardine boom of the 1980s.

That does not make harvest control less important. It makes it more important. Managers cannot set the Kuroshio, ocean temperature or basin-scale food webs. Fishing mortality is one of the large pressures they can actually change.

ABC is advice; TAC is a management decision

Numbers such as 162,000 tonnes for Pacific sardine or 527,000 tonnes for the Tsushima stock are easy to mistake for announced quotas. They are not. ABC is produced from the stock assessment and a specified harvest scenario. TAC is established through the management system for designated stocks, informed by scientific advice but also through the formal process that defines management objectives and harvest scenarios.

The distinction is even more important for stocks whose documents use terms such as “proposed target reference point,” “proposed harvest-control rule” or “ABC estimate.” Japan is still expanding and standardizing management across fisheries with very different data quality and fleet structures. A scientific assessment can be precise about what it knows without pretending the policy decision has already been made.

What the numbers do—and do not—mean for seafood buyers

A stock assessment is not a short-term price forecast. A lower resource level does not mechanically mean higher supermarket prices next week, and a stock above target does not guarantee cheaper fish. Landings depend on where schools move, weather, fuel, labor, port capacity, cold storage, imports and demand. The assessment is about preserving biological production over time.

For fishing communities, however, the stakes are immediate. Reducing fishing pressure can cut landings and income in the short run. Delaying action until a stock collapses can create a far longer economic shock. That tension is why modern fisheries policy cannot be reduced to biology alone; it has to connect biology to allocation, transition support, monitoring and the lived economics of fleets and ports.

Japan’s sea is not one report card

The September release resists a simple headline. Pacific sardine is below target with unusually high fishing pressure. Tsushima sardine is above target. Pacific anchovy is above target with low fishing pressure. Round herring is below a proposed limit. Red seabream depends partly on assumptions about hatchery releases. Two scad assessments use a data-limited rule because the information required for a full age-structured model is not available.

That complexity is not a weakness of the assessment. It is the reality the assessment is designed to expose. A fishery is a biological population in a changing ocean, harvested by real fleets, observed through imperfect data and governed through institutions that must make choices before uncertainty disappears.

Japan learned in the sardine collapse that a sea that looks inexhaustible can change within a generation. The 2026 numbers do not say history is repeating. They do provide something Japan did not always have: a much broader, more explicit system for seeing the change while there is still time to decide what to do about it.