ICES Stock Identification Methods Working Group (SIMWG)

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 2023, 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 two working documents on the stock definition of a) Baltic Sea dab (dab.27.22-32) and North Sea dab (dab.27.3a4), and b) flounder in the Belt Seas and the Sound (fle.27.22-23) and North Sea flounder (fle.27.3a4). Moreover, SIMWG members co-chaired and participated in the Workshop on the Evaluation of NEA Mackerel Stock Components (WKEVALMAC) and the Second Workshop on Stock Identification and Allocation of Catches of Herring to Stocks (WKSIDAC2). 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’s 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.