The Stock Identification Methods Working Group (SIMWG) reviews new methods for the definition and investigation of stock structure and provides recommendations to other ICES expert groups on how to interpret patterns of population structure.

In 2024, SIMWG has continued providing annual updates on recent applications of stock identification methods to species assessed by ICES and on advances in stock identification methods. Based on the wide expertise of SIMWG members, we provide reviews of recent literature on genetics, growth marks in calcified structures, life history parameters, morphometrics/meristics, tagging, otolith shape, otolith chemistry, parasites and interdisciplinary approaches.

A key activity of SIMWG is to address requests by ICES working groups for technical recommendations on issues of stock identity. In the current term, we reviewed working documents (WDs) by the Working Group on the Biology and Assessment of Deep-sea Fisheries Resources (WGDEEP) on the stock structure of blue ling and by the Benchmark Workshop on Horse Mackerel and Boarfish stocks (WKBHMB) on northern and western horse mackerel. During the SIMWG online meeting, the group assessed WDs on the stock boundaries of anchovy (request by the Working Group on Southern Horse Mackerel, Anchovy, and Sardine (WGHANSA)) and Baltic dab, flounder and plaice (joint request by the Baltic Fisheries Assessment Working Group (WGBFAS) and the Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK)).

Moreover, SIMWG members co-chaired and participated in the Third Workshop on Stock Identification and Allocation of Catches of Herring to Stocks (WKSIDAC3). There also is a strong link to the Working Group on the Application of Genetics for Fisheries and Aquaculture (WGAGFA).

SIMWG contributes to the general understanding of the biological features of the north Atlantic ecosystem through its work to describe fish population structure. Additionally, SIMWG annual reviews on advances in stock identification methods keep ICES members abreast of best practices in this field of study. SIMWG expert reviews on questions of stock structure for particular ICES species are directly relevant to the appropriate definition of stock and contribute to the accuracy of stock assessment and effectiveness of management actions. We see an important role for SIMWG in the future as ICES copes with the shifting distributions of fishery resources and questions regarding the appropriate definition of fish stocks. Understanding stock structure is a fundamental requirement before any assessment or modelling on a stock can be contemplated and SIMWG will continue to work with ICES expert groups to address pressing stock identification issues.