Stock distributions in Atlantic Herring: tracking population

Management areas of Atlantic herring stocks are often not aligned with biological units. Thus, a single management area may support multiple populations and ecotypes, varying in distribution in time and space and underlying highly differentiated dynamics. With the application of genetic characterization and monitoring of individual populations, we gain increasing understanding of changing dynamics, including effects of climate and human use. For example, the last several decades of dwindling recruitment in spring spawning herring in the Western Baltic Sea-Kattegat-Skagerrak could potentially be affected by a seeming changing balance between this population complex and an autumn spawning herring ecotype from the same area, that historically used to be dominating the fishery catches, but apparently crashed and is not currently managed as a separate stock component. Through previous EHFAF projects DTU Aqua has built up a unique herring DNA database and has implemented genetic stock identification in data collection, allowing for a much deeper understanding of stock dynamics in time and space. However, to be fully efficient, methods need to be internationally integrated in data collection and stock assessment. Work done in HERMIX is aimed at extending data over time series and facilitating international integration in collaboration with research institutes, including in Sweden and Germany. Geographical focus is on herring caught in the North Sea and Skagerrak (the include Western Baltic spring spawning herring), but also include herring in the Western Baltic Sea. Two main objectives are to improve stock assessment data, and to improve the basis for real-time monitoring, through development and test of eDNA based tools that may allow for more optimal exploitation of strong stocks, while safe-guarding vulnerable stocks. The generated knowledge is implemented in national and international advice related to the EU common fisheries policy and on stocks shared by EU, Norway and the UK.