ICES Report Places Cod Under Scrutiny in June 2025 Stock Annex

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A new ICES report thoroughly examines cod stocks across European waters, detailing population structures, fishing impact, and ecological factors

The International Council for the Exploration of the Sea (ICES) has published its June 2025 stock annex. This report offers an in-depth analysis of cod (Gadus morhua) populations.

The areas covered include Subarea 4, divisions 6.a and 7.d, and Subdivision 20. This expansive region encompasses the North Sea, West of Scotland, eastern English Channel, and Skagerrak. The report provides a crucial overview of these commercially vital fish stocks.

Complex Cod Population Structures

The report highlights the intricate population structure of cod within these regions. ICES workshops on stock identification (WKNSCodID 2020 and WK6aCodID 2022) revealed that North Sea cod are distinct. They differ from those in the Faroe Plateau and Norwegian Coastal Cod populations.

However, the North Sea itself hosts reproductively isolated groups. These include Viking and Dogger cod, which exhibit some spatial overlap and post-spawning mixing. The Skagerrak and northern Kattegat serve as key nursery grounds, predominantly for Viking cod.

Further complexity arises from genetic and phenotypic variations. Viking cod primarily inhabit the northeast North Sea, extending westward to the Shetlands, with nurseries in the Skagerrak. Dogger cod occupy the south-central North Sea, along the Scottish coast, and into the eastern English Channel.

While genetic homogeneity within Dogger cod is unclear, a phenotypic spatial structure exists. This is roughly delineated by the 50m bathycline in the central North Sea. Cod north of this boundary (Northwestern sub-stock) show different growth rates, maturity, and biomass trends compared to those south (Southern sub-stock).

The West of Scotland (Division 6a) exhibits multiple overlapping subpopulations. These are linked to the Dogger genetic lineage, with a separate Clyde sub-population associated with the Celtic lineage. Tagging data confirms limited mixing for Clyde cod, which are largely resident within the Clyde, distinct from other 6a sub-populations.

Despite these complexities, a separate assessment for Clyde cod is currently impractical due to limited disaggregated data. Its minor catch contribution means its inclusion in a broader meta-population assessment is deemed acceptable for the short to medium term.

Fisheries and Management Measures

Cod are caught by almost all demersal gears in Subarea 4, Division 7.d, and Subdivision 20. These include beam trawls, otter trawls, seine nets, gill nets, trammel nets, and lines. While cod can be a bycatch in some fisheries (e.g., beam trawls targeting flatfish), other operations, particularly fixed gear fisheries, directly target cod.

Total fishing effort in the North Sea has significantly declined since 2003. Otter trawls remain the most prevalent gear in the Greater North Sea. In the northern North Sea and Skagerrak, otter trawls with mesh sizes exceeding 100mm target a mix of species including cod, haddock, and whiting.

This directed roundfish fishery (demersal trawls and seines with >100mm mesh) is the primary driver of cod impact. It accounted for 67-75% of landings between 2017–2021.

Management regulations include a minimum conservation reference size of 35 cm for cod in this area (Regulation (EU) 2019/1241). The EU landing obligation, implemented from January 2017 under Article 15 of Regulation (EU) No 1380/2013, also applies to various gears, including otter trawlers with mesh sizes over 100mm.

Furthermore, area closures have been established to protect cod. Examples include a seasonal closure off Northern Ireland and a cod protection area in the North Sea.

Ecosystemic Influences on Cod Health

Ecological factors play a critical role in cod stock dynamics. Natural predators, including harbour porpoises, grey seals, and even cannibalism, significantly impact cod aged 1-2 years. For older cod (3-4 years), grey seals are almost exclusively responsible for predation mortality.

However, uncertainty remains regarding whether seals exploit the same cod populations as commercial fisheries. Seal foraging often occurs in rocky, untrawlable areas not covered by surveys. This suggests seals and fisheries may be operating on different sub-stocks, highlighting the complexity of natural mortality assumptions for Northern Shelf cod.

Recruitment, the process by which young fish are added to the fishable population, is influenced not only by spawning stock biomass (SSB) but also by environmental factors. These include water temperature, plankton production timing, mean prey size, the North Atlantic Oscillation (NAO), and the demographic composition of spawning fish.

The report integrates extensive data. This includes commercial catch figures, discard rates, and comprehensive survey data from the first, third, and fourth quarters. It assesses cod ages from 1 to 7 years and older. This data is crucial for understanding the stock’s overall health and regional trends.

Stock annex: Cod (Gadus morhua) in Subarea 4, divisions 6.a and 7.d, and Subdivision 20 (North Sea, West of Scotland, eastern English Channel and Skagerrak)