One Sardine Stock Is Flashing Red. Another Is Above Target.

Japan’s newest fisheries assessments do not support a simple national story of “more fish” or “fewer fish.” The strongest contrast is within a single species. The Pacific stock of Japanese sardine ended 2025 with spawning biomass at 72% of the level associated with maximum sustainable yield and estimated fishing pressure at 4.43 times Fmsy. The Tsushima Current sardine stock, meanwhile, sat just above its spawning-biomass target with fishing pressure at only 37% of Fmsy.

The Pacific sardine stock is the clearest warning

The Pacific Japanese sardine stock had been one of the great comeback stories of Japan’s seas. Biomass rose after 2009 and exceeded five million tonnes in 2022. But recruitment—the number of young fish entering the stock—has declined since 2023. Total biomass fell to 1.694 million tonnes in 2025, while spawning biomass fell to 1.035 million tonnes.

The MSY spawning-biomass target, SBmsy, is 1.432 million tonnes. The 2025 stock therefore stood at 0.72 SBmsy. More strikingly, the assessment estimates fishing pressure at 4.43 times Fmsy. On the Kobe plot, the stock has moved back into the combination managers most want to avoid: below-target spawning biomass with above-reference fishing pressure.

There is an additional forward-looking signal. The spawning index increased strongly after 2010 but has fallen since 2023; the provisional 2026 value dropped to levels last seen during the weak 2000s. Several recruitment and age-one indices have also weakened over the past two or three years.

This does not mean the stock is on the edge of extinction. It means the population has moved away from the biomass-and-fishing combination designed to produce sustainable long-run yield, after several years in which spawning biomass had been above target.

West of Japan, the same species tells a different story

The Tsushima Current sardine stock, spread through the East China Sea and Sea of Japan, is in a very different position. Biomass has risen since 2020 and reached 2.096 million tonnes in 2025. Spawning biomass was 1.149 million tonnes, just above the SBmsy target of 1.089 million tonnes.

Fishing pressure was only 0.37 Fmsy. The stock therefore occupies the desirable side of the Kobe plot: biomass above target and fishing pressure below reference. Recruitment fell to 15.6 billion age-zero fish in 2025, so the trajectory is not guaranteed, but its immediate management position is far less stressed than the Pacific stock.

Both fish may reach Japanese markets under the same common name. Biologically and managerially, they are different populations responding to different oceanography and fisheries.

Japanese jack mackerel is below target on both sides of the country

The Pacific stock of Japanese jack mackerel had 64,000 tonnes of total biomass and 25,000 tonnes of spawning biomass in 2025. Its SBmsy target is 52,000 tonnes, leaving spawning biomass at 0.48 of target. Fishing pressure was slightly above Fmsy at 1.12.

There are nevertheless signs of rebuilding. Recruitment improved in 2023 and the 2025 estimate, 750 million age-zero fish, was similar to 2023. Total biomass has recovered from 36,000 tonnes in 2021 to 64,000 tonnes in 2025. The problem is that the adult spawning base remains only about half the target.

The Tsushima Current jack-mackerel stock is much larger—304,000 tonnes of biomass in 2025—but spawning biomass was 158,000 tonnes against an SBmsy of 273,000 tonnes, or 0.58 of target. Fishing pressure fell to 0.65 Fmsy. The deeper issue is recruitment: age-zero abundance has remained below three billion fish since 2020, a low level relative to earlier decades.

In other words, low fishing pressure alone does not instantly rebuild a stock. The number of young fish produced by the ocean still determines how much raw material management has to work with.

Anchovy is above target; round herring is below its proposed limit

Pacific Japanese anchovy has moved in the opposite direction. Biomass and spawning biomass declined from the mid-2000s but have risen since 2019. The 2025 assessment estimated total biomass at 377,000 tonnes and spawning biomass at 165,000 tonnes—1.47 times its SBmsy target of 112,000 tonnes. Fishing pressure was only 0.25 Fmsy.

Pacific round herring is more concerning, but its assessment uses a different system. A standardized abundance indicator of 0.86 corresponds to the 28.7th percentile of the historical resource-level distribution. The proposed target is the 80th percentile and the proposed limit is the 56th. In that framework, the 2025 stock sits below the proposed limit level.

Catch peaked at 49,000 tonnes in 2015 and fell to 21,000 tonnes in 2025. The estimated 2027 acceptable biological catch under the proposed rule is 17,000 tonnes.

The two numbers—anchovy at 1.47 SBmsy and round herring at 28.7% resource level—cannot be compared arithmetically because the models differ. They can be compared directionally: one stock is above its MSY spawning target; the other is below its proposed limit under a data-limited rule.

Splendid alfonsino is rebuilding; red sea bream has a Japan-specific wrinkle

Pacific splendid alfonsino has improved from a biomass low of 29,500 tonnes in 2015 to 43,700 tonnes in 2025. Spawning biomass reached 29,700 tonnes, or 1.22 SBmsy, while fishing pressure was 0.66 Fmsy. Since 2019, the assessment has placed fishing pressure below the MSY reference.

The western Japan Sea / East China Sea red sea bream stock is more unusual. Total biomass was 19,500 tonnes in 2025 and spawning biomass 13,100 tonnes. A conventional SBmsy is calculated at 39,300 tonnes, but management uses a provisional target called SB84%msy—13,100 tonnes—based on the maximum sustainable yield for ages one through six and a framework that explicitly incorporates hatchery releases.

The 2025 spawning biomass was exactly at that provisional target, and fishing pressure was 0.84 of the corresponding F84%msy reference.

That management structure reflects a long Japanese history of stock enhancement. Juvenile red sea bream have been released in the region since the late 1970s. Future projections explicitly include an assumed contribution from released juveniles, based on the recent average. It is therefore not a purely wild-recruitment model.

Japanese scad clears its target; muroaji scads sit just below theirs

The western Japan Sea / East China Sea stock of Japanese scad is assessed with standardized catch-per-unit-effort rather than a full age-structured MSY model. Its 2025 abundance index of 1.44 corresponds to the 82.9th percentile of the historical resource-level distribution—slightly above the proposed 80% target. The assessment calculates a 2027 ABC of 3,811 tonnes.

The East China Sea “muroaji” scad group had an index of 1.11, corresponding to the 73.3rd percentile. That is below the proposed 80% target but above the 56% limit. The 2025 catch was 4,086 tonnes.

These are good examples of why the national system needs more than one model. For some fisheries, scientists have age composition, spawning biomass and recruitment histories sufficient for MSY-based models. For others, the most reliable long time series is standardized CPUE. The management question is the same—how hard can the fishery operate without eroding the resource—but the statistical route differs.

The Kobe plot is a fisheries traffic light

For the MSY-based assessments, the most intuitive chart is the Kobe plot. The horizontal axis is spawning biomass relative to SBmsy. The vertical axis is fishing pressure relative to Fmsy. To the right means more adult spawning biomass; downward means lower fishing pressure.

The desirable quadrant is therefore the lower right: spawning biomass at or above target and fishing pressure below the level associated with maintaining MSY. The upper left is the warning combination—below-target spawning biomass and above-reference fishing pressure.

Pacific sardine is now in that warning quadrant. Tsushima sardine, Pacific anchovy and Pacific splendid alfonsino are on the favorable side. Both jack-mackerel stocks remain below the spawning target, though the Tsushima stock’s fishing pressure is already well below Fmsy.

The chart is not an extinction meter. Falling below SBmsy does not mean a stock is biologically collapsing. It means the stock is below the spawning biomass expected to support maximum sustainable yield. Lower limit and closure thresholds are separately defined.

MSY is not simply “catch as much as possible”

Maximum sustainable yield is the largest long-run average catch expected from a stock under specified biological assumptions without driving it into continuing decline. Japan’s post-2020 management system uses scientific assessment to define stock targets and then links those targets to total allowable catch, or TAC, and harvest-control rules.

When a stock is low, fishing pressure is reduced to rebuild spawning biomass. When the stock is above target, catches can rise within the rule. The policy logic is therefore not “catch less forever.” It is to sacrifice some short-term extraction when necessary to create a larger and more stable long-run fishery.

But MSY is not a fixed property of an unchanging ocean. Recruitment can swing sharply with temperature, food supply, currents, predator pressure and spawning success. The Japanese assessments use stock-recruit relationships and thousands of stochastic simulations, but future ocean conditions can still differ from the historical range used to fit those models.

Japan has changed how it counts fish

The modern framework dates to the revised Fisheries Act that took effect in December 2020. Japan made TAC-based management the basic tool and rapidly expanded scientific assessment. According to the Fisheries White Paper, the number of assessed species rose from 50 in FY2018 to 192 by FY2021. By FY2025, MSY-based reference points had been developed for 22 species and 40 stocks.

The government’s roadmap targets a recovery of capture production—excluding aquaculture and seaweed—to 4.44 million tonnes by FY2030, roughly the 2010 level. It also aims to have at least 60% of MSY-assessed stocks at or above MSY biomass levels.

The larger change is methodological. Catch is no longer treated as a simple proxy for abundance. Scientists combine age composition, survey indices, CPUE, spawning surveys, recruitment and adult biomass to estimate the underlying population and the fishing mortality being applied to it.

Japanese sardine once helped push national production to its all-time peak

Sardine history explains why managers are cautious about interpreting a boom as permanent. Japan’s total fisheries and aquaculture production peaked at 12.82 million tonnes in 1984. One major reason was an enormous increase in Japanese sardine during the period when distant-water fisheries were already being constrained by the global spread of 200-nautical-mile exclusive economic zones.

The sardine boom did not last. Sardine abundance collapsed as ocean conditions shifted, contributing to the sharp national production decline into the mid-1990s. The Fisheries Agency explicitly discusses large-scale “regime shifts” in ocean-atmosphere conditions as one factor behind the historic sardine cycle.

Japan produced only about 3.64 million tonnes of fisheries and aquaculture products in 2024—less than 30% of the 1984 peak. That long decline cannot be blamed on a single management failure. Loss of distant-water fishing grounds, fewer vessels and fishers, resource depletion, changing demand and processing, and changing ocean conditions all contributed.

The ocean being managed is itself moving

Japan’s fisheries policy now has to manage populations in one of the world’s rapidly warming marine regions. The Fisheries Agency says average sea-surface temperature around Japan rose about 1.33°C per century through 2024, more than twice the global long-term rate cited in the same white paper.

Marine heatwaves have become more visible since around 2010. The Kuroshio and its extension, and the southward reach of the Oyashio, have shifted. Fisheries are already experiencing altered distributions: species such as yellowtail and Spanish mackerel have expanded or moved in some regions, while Pacific saury, Japanese flying squid and salmon have suffered long-running changes in availability.

That does not mean every change in the ten September assessments can be attributed to climate change. The Pacific sardine decline, for example, has to be understood through recruitment, fishing pressure and broader environmental dynamics together. But it does mean historical stock-recruit relationships are being asked to operate in a moving physical system.

A good assessment is not the same thing as tomorrow’s catch limit

The scientific assessment estimates biomass, fishing pressure and future probabilities. It is an input to management, not identical to a quota decision. Harvest scenarios, TAC or ABC settings also have to interact with fleet economics, mixed fisheries, international catches and regional communities.

For example, the Pacific jack-mackerel assessment calculates a 2027 ABC of 26,000 tonnes under its β=0.9 harvest scenario. Under that rule, the probability that spawning biomass exceeds the 52,000-tonne target in 2036 is estimated at 55%. That is not a guarantee; it is a probabilistic tradeoff.

The same logic applies when a stock is above target. Harvest can rise, but maximising extraction immediately can increase the risk that a weak recruitment year pushes the population below target again. Modern harvest rules are designed to smooth that risk.

Japan’s sea is simultaneously recovering and flashing warnings

Put the ten assessments together and the picture is deliberately messy. Tsushima sardine, Pacific anchovy and splendid alfonsino are above their MSY spawning targets. Japanese scad is above its index-based target. Red sea bream is at its special provisional target.

Both jack-mackerel stocks remain below target. Pacific sardine has dropped below target with sharply elevated fishing pressure. Pacific round herring is below its proposed limit level. Muroaji scads remain below target.

That is neither a story of national fisheries collapse nor one of broad recovery. It is a story of populations moving at different speeds in different oceans.

On a Japanese dinner table, aji, iwashi and tai are ordinary categories. In the water, they are dynamic populations with different spawning grounds, age structures, ocean currents and fishing histories. The ten assessments published on September 2 are best understood as a health check: not simply how many fish were caught, but whether enough adults remain to produce the next generation.