EU, Norway & UK Seek Genetic Roadmap for Northern Shelf Cod

EU, Norway and UK request ICES guidance on genetic sampling to support future area-based Northern Shelf cod advice

Joint Request Seeks Area-Based Cod Advice Framework

The EU, Norway and the UK have formally requested guidance from the International Council for the Exploration of the Sea on how to move towards area-based catch advice for Northern Shelf cod, placing genetic sampling at the centre of the process.

In advice published on 20 February 2026, ICES responds to the joint request by setting out a proposed multiyear pathway for developing spatially differentiated management of the Northern Shelf cod complex. ICES makes clear that progress will depend on securing sufficient funding and coordinating sampling across countries.

The request follows changes introduced in 2023, when cod in the North Sea and West of Scotland were merged into a single assessment unit – Northern Shelf cod – comprising three substocks: Southern, Northwestern and Viking. ICES previously stated it could not provide area-specific catch advice without routine genetic data from both commercial fisheries and scientific surveys.

Genetics Identified as Core Tool

ICES advises that genetics is a suitable tool for distinguishing between the three substocks and that pilot studies should begin collecting genetic samples in 2026 if the proposed timeline is to be met.

New genomic work under the GenDC project provides evidence of genetic differentiation between spawning cod from the Northwestern, Viking and Southern areas. The Viking substock exhibits distinct frequencies in a large region on chromosome 12 and other genomic regions. The Southern substock also forms a distinguishable group from the other two, with separation observed across the genome rather than being limited to a few regions.

ICES concludes that there is potential to develop a genetic marker set capable of assigning individual fish to substocks. However, it notes that the biological drivers behind the observed genetic differences remain uncertain and may relate to local adaptation and reproductive isolation.

In the short term, ICES advises that full genome sequencing of existing samples could provide additional insight into stock mixing and help refine advice, although it acknowledges that this approach would not be cost-effective in the long term.

Tagging and Other Methods Reviewed

ICES also reviewed non-genetic methods for understanding stock structure and mixing.

A reanalysis of historical tagging data from 1961 to 2015 indicates strong site fidelity for cod released in the Northwestern and Southern areas, with most fish remaining within their substock boundaries. Cod released in the Viking area showed greater movement, particularly towards the Northwestern area.

Data storage tag tracks confirmed that most movement occurs within substock areas, with cross-boundary migration mainly occurring near borders. However, ICES highlights limitations in the tagging analysis, including lack of recent data and the absence of genetic confirmation of substock origin for tagged fish.

Otolith shape analysis did not provide strong discrimination between substocks, although otoliths are routinely collected and could support future work. Otolith microchemistry has demonstrated potential to identify natal origins and migration patterns, but ICES notes that it is substantially more expensive than genetic analysis.

Overall, ICES considers genetics to offer the most direct route to operational substock identification, with tagging and otolith approaches acting as complementary tools.

Pilot Studies and Data Integration

The proposed pilot studies are intended to assess the feasibility of routine genetic sampling from both fisheries-independent surveys and commercial catches, improve the genetic baseline, and define a multiannual sampling design.

Quarter 1 surveys are considered critical because they sample spawning fish and strengthen the genetic reference baseline. Commercial sampling would provide information on substock composition in catches throughout the year.

ICES notes that if all cod sampled for age in recent years had also been sampled genetically, more than 10,000 genetic samples could have been obtained in a single year. It cautions, however, that funding and coordination will determine whether such sampling levels are realistic.

The organisation also recommends integrating genetic data into existing ICES databases and developing a dedicated metadata system. Storage of raw genotype data in a centralised database would require additional funding.

Assessment Models and Management Implications

ICES examined how different stock assessment models could incorporate substock composition data. Multistock state-space assessment models (SAM) are capable of using raw genetic data directly, while other spatially structured models rely on approximating substock membership by area.

A preliminary simulation using a multistock SAM suggests that incorporating genetic data could reduce uncertainty and relax certain assumptions regarding fishing mortality. ICES advises that a broader simulation study be conducted to evaluate trade-offs between sampling intensity, yield and biological risk.

In the short term, emerging genetic insights may allow ICES to refine advice and potentially recommend mitigation measures, such as avoiding fishing in specific areas where vulnerable substocks are present.

In the longer term, once substock mixing can be quantified with confidence, ICES states that area-based catch advice could be developed, provided that data support it.

The advice makes clear that the transition to spatially differentiated management of Northern Shelf cod is contingent on sustained funding, coordinated sampling and multiannual scientific effort.