Workshop on scoping data collection for northern shelf cod sub-stocks (WKCODSCOPE; outputs from 2025 meeting)

The WKCODSCOPE workshop brought together representatives from 11 countries and institutions, including participants from both the scientific community and the fishing industry. In total, 47 individuals attended. The workshop was chaired by Côme Denechaud (Norway), Liz Clarke (UK), Marie Storr-Paulsen (Denmark), and Nicola Walker (UK).

In 2023, ICES redefined the Northern Shelf cod stock by merging West of Scotland and North Sea cod into a single assessment unit with three sub-stocks: northwestern, Viking, and southern. To enable area-specific advice, more routine genetic sampling from fisheries and surveys is needed. Norway, the UK, and the EU have requested ICES to develop a comprehensive genetic sampling design to better understand sub-stock dynamics and stock mixing. ICES initiated a two-workshop process, with WKCODSCOPE being the first.

During the workshop genetic studies were presented that confirmed genetic differentiation of North Sea cod into two main populations “Viking” and “Dogger.” However, earlier research was limited by few genetic markers and restricted sampling. A new project, GenDC aims to resolve these limitations and has collected and will finalize sequencing of spawning cod from the southern North Sea to determine whether a distinct sub-population exists there. These genetic results will be compared with data from Viking and northwestern areas to strengthen the baseline for population assignment. Results from southern spawning cod will be analyzed before the next WKCODSCOPE meeting to guide future sampling and stock assessments.

During the workshop tag-recapture data (1961–2015) were reanalyzed and showed limited mixing among the three sub-stocks, Northwestern, Southern, and Viking, though some border movement exists, especially between Viking and Northwestern regions. New tagging programs are recommended to update movement data and validate genetic findings.

During the workshop complementary approaches such as otolith morphology and chemistry were being presented to explore if this could be used to identify population structure and mixing. Otolith shape analysis offers a simple, cost-effective tool for distinguishing sub-stocks, though it can be influenced by environmental variation. Otolith chemistry provides insights into natal origin, life-history migrations, and mixing patterns, potentially serving as a powerful alternative or complement to genetics, especially where genetic differentiation is weak.

Further, a suggested sampling plan was discussed during the workshop and for commercial fisheries, future work should focus on designing and piloting sampling schemes that combine genetic and otolith data from market landings or onboard collections. Multi-stage sampling designs will account for variability among vessels, trips, and hauls. Pilot surveys planned for 2025–2026 will test protocols and determine required sample sizes, with the goal of developing a coordinated regional sampling scheme across nations.

A standardized onboard genetic sampling protocol has been developed under GenDC, detailing equipment, procedures, and storage methods. It aligns with DATRAS data formats for streamlined integration into ICES databases. Consistent application of this protocol, alongside further refinement for commercial settings, will be key to achieving reliable, comparable data for cod stock assessment and management across the Northern Shelf.