Wrong Fish, Wrong Quota: ICES Report Finds Herring Being Caught Under the Wrong Stock
A new ICES scientific report has confirmed what many fishermen working the Irish and Scottish grounds have long suspected: the boundaries used to manage and assess western herring stocks do not match how the fish actually move.
The Workshop to Review the Ecology of Western Herring Stocks (WKREHERS), published this year as ICES Scientific Reports Volume 8, Issue 53, followed a 2025 UK initiative, the Workshop on Ecology of Herring in the Irish Sea and Implications for Management (WKNIRSMAN), held at the Agri-Food and Biosciences Institute in Belfast, which first raised concerns about the extent of stock mixing in the Irish Sea. Chaired by Campbell Pert of the UK’s Marine Directorate, WKREHERS met online on 17 February 2026 with 16 participants drawn from Ireland, the UK, Denmark, and Norway.
ICES currently provides catch advice for five herring stocks in the Celtic Seas: west of Scotland autumn spawners (her.27.6aN), the northwest and west of Ireland stock (her.27.6aS7bc), Irish Sea autumn spawners (her.27.nirs), Celtic Sea winter spawners (her.27.irls), and herring in the western English Channel and Bristol Channel (her.27.7ef). Between them these stocks accounted for 175,060 tonnes of catch from 2015 to 2024, each with its own annual TAC. A handful of smaller populations, including spring spawners in the Minch and Firth of Clyde herring, sit outside the ICES advice process entirely.
Mixing is the rule, not the exception
The workshop’s central conclusion is blunt: genetic sampling now confirms that herring caught in the Irish Sea acoustic surveys and fishery are a mix of Irish Sea autumn spawners and fish originating in the Celtic Sea, and that this mixing runs across all age classes, not just juveniles as previously assumed. A 2022 genetic study of Irish Sea commercial and survey samples found that in some catches, as little as 30% of the fish sampled were genuine Irish Sea stock, with the remainder assigned to what the report terms the wider “Celtic Seas” population.
The report also settles a long-running question over west of Scotland autumn spawners: genetic testing confirms 6.aN autumn spawners and North Sea autumn spawners are the same biological population, undermining the case for treating them as separate stocks divided by the 4°W line, a boundary the report notes was drawn for statistical convenience in the 1950s rather than for any biological reason.
Other headline points
- A spring-spawning population in 6.aN, observed spawning in the Minch in recent years, is not currently assessed or covered by any TAC, despite possibly now outnumbering the assessed autumn-spawning component.
- The her.27.6aS7bc stock is a mix of winter and spring spawners showing a genetic continuum rather than a clean split, and both groups migrate across the 4°W line into North Sea waters, movement not accounted for in any current assessment.
- Herring in the western Channel and Bristol Channel (her.27.7ef) only received their first formal ICES catch advice in 2025, based on a precautionary 20% cut to the ten-year average landings, because there is still no reliable abundance survey for the area.
- aN autumn spawners recorded their lowest spawning stock biomass on record in 2025, continuing a run of poor recruitment. Celtic Sea herring (her.27.irls) has been below the biomass limit reference point, Blim, since 2016.
What this means for Irish fishermen
For the south coast fleet working out of Dunmore East, Waterford, and Cork, the Celtic Sea stock (her.27.irls) is the most exposed of the five. It has been below Blim, the biomass limit reference point, since 2016 and has fished under an 869 tonne monitoring TAC since 2020, split between an offshore fleet in divisions 7.g and 7.j and an inshore fleet in the southern Irish Sea. The report confirms Celtic Sea fish are also being caught in significant numbers in the Irish Sea fishery west of the Isle of Man, but that additional fishing pressure is not currently counted against the Celtic Sea assessment. An already depleted stock may be absorbing more fishing mortality than its own TAC accounts for, simply through a different fishery’s nets.
Vessels fishing west of the Isle of Man face a similar issue in reverse. Commercial samples collected from Irish boats targeting Irish Sea herring in 2019 and 2020 were genetically assigned roughly 70% to Celtic Sea origin, with only around 30% genuine Irish Sea stock. The current assessment (her.27.nirs) is run on the mixed catch without separating the two. Once that catch is split by genetics, quota and effort in that fishery could be redistributed.
For the Donegal fleet working her.27.6aS7bc, historic catch figures are confounded because genetic sampling to separate winter and spring spawners from 6.aN autumn spawners has only run since 2022; everything before that relies on a rough retrospective split. The stock has also been shown migrating across the 4°W line into North Sea waters in ways the assessment does not track, and the Malin Shelf survey used to index the stock has containment issues on the same boundary. This does not threaten the fishery directly but means more uncertainty sits behind the TAC than the headline advice suggests.
The general direction of travel for stocks with confirmed mixing has been toward more caution rather than less; ICES already moved to more conservative, mixed-stock-aware advice for Irish Sea herring in 2024 for this reason. Irish vessels can expect continued or increased requests for genetic sampling at sea and on the dockside in the meantime. The scheduled 2027/2028 benchmark for Irish Sea herring is the point where quota-setting methodology for that fishery is most likely to actually change.
What happens next
The workshop sets out a roadmap of further work, including expanded genetic baseline sampling in the Irish Sea, Celtic Sea, and Firth of Clyde, and a push toward a single coordinated “synoptic” acoustic survey covering the Irish Sea, Celtic Sea, and English Channel together, rather than the patchwork of separate surveys currently run by different national institutes. A feasibility workshop for that synoptic survey, WKFICES, is already underway in 2026. The Irish Sea herring assessment (her.27.nirs) is scheduled for a full benchmark review in the 2027/2028 cycle, with a second, joint benchmark covering both Irish Sea and Celtic Sea stocks proposed for later years. A possible follow-up workshop, WKREHERS2, has been pencilled in for 2027 to coincide with the Herring Assessment Working Group.
