Workshop on sampling data for northern shelf cod sub-stocks (WKCODSAMPLING)

WKCODSAMPLING brought together scientific experts and representatives from the industry in a second workshop, following WKCODSCOPE (18-21 March 2025), to address a request from Norway, UK, and EU to ICES for advice on developing a biological sampling programme, with a focus on genetic data, to support the management of the Northern Shelf cod.

WKCODSAMPLING reviewed the status of the GenDC project. Results from the genomic analyses strongly suggested that the Southern component has a unique genetic profile, which is a first important prerequisite for developing a sampling programme for the collection of genetic data. Consequently, the workshop recommended to proceed with the design of a genetic sampling programme, which could also include additional biological sampling (e.g. otoliths for shape analyses) and can be linked to existing data collection frameworks and infrastructure. Protocols to support on board sampling have been developed and can be modified accordingly to accommodate national needs and priorities.

On a short-term, it will be possible to conduct additional genomic analyses on samples already collected to provide qualitative information to support advice under the “ICES Guidelines for advice on fisheries that concurrently catch a mix of stocks of the same species”. The strengthening of the genetic baseline should be prioritized through the collection of spawning cod in Q1 surveys and targeted sampling of catches. The further development of an operational genetics-based tool for monitoring and management is recommended but is not within the remit and timeline of GenDC.

Genetic data is currently integrated with existing ICES databases as two separate fields: population assignment and associated probabilities. A thorough documentation of the underlying genetic methodology (baselines, genetic marker panels etc.) is important to secure re-producibility and transparency, and it is recommended to have a database to store underlying genotype data that can be directly linked to the existing database structure developed by ICES.

The analysis of otolith shapes provided mixed signals on the separation of the three sub-stocks using shapes alone, but did highlight morphological differences of interest in Viking cod. It is recommended to include digital imaging of otoliths from the individuals of interest to the genetic baseline in 2026, with shape analysis to be carried out concurrently. Reanalysis of tagging data provided new perspectives on the historical mixing patterns discussed during WKCODSCOPE. Further tagging work, especially individual tagging using DSTs, will be useful to quantify local movement across boundaries and confirm whether mature fish show high site fidelity during quarter 1.

Assessment models that can include stock composition data were summarized in terms of data needs, assumptions, limitations and relevance to Northern Shelf cod sub-stocks. Simulation studies with the multi-stock SAM assessment model showed genetic data could reduce uncertainty and, if available throughout the time-series, allow estimation of individual fishing mortalities when the underlying assumptions are correct.

Further work, using the powerful combination of insights from tagging, morphological characteristics and genetics, is needed to understand the spatio-temporal dynamics and patterns of mixing in the Northern shelf cod complex. This will require dedicated funding.