Project name: Revealing Mysid abundances to better understand changes in herring condition in the Baltic Sea

forthcoming

Goal: this proposal aims at (1) improving the scientific knowledge regarding the abundance and distribution of large crustacean plankton – especially mysid shrimps – in the Baltic Sea, (2) understand the dynamics of herring predation upon mysids and large crustacean plankton, as a driver of herring body condition and growth, and (3) define an operational framework for monitoring the abundance of mysids and large crustacean zooplankton in the Baltic Sea. Rationale: mysids and Limnocalanus macrurus were observed to be suddenly scarce in the Northern Baltic Sea in 2021, which resulted in a significant alteration of the body condition of herrings above age 3, particularly in the Gulf of Bothnia, and had significant consequences on the spawning stock biomass (SSB) and the resulting catch advice for this stock. In this context, and following a special request by the EU Directorate-General for Maritime Affairs and Fisheries (DG MARE), the International Council for the Exploration of the Sea (ICES) established a roadmap for possible conservation measures for herring in the Baltic (ICES, 2024). This roadmap underlined the importance of mysid monitoring. Furthermore, the importance of mysids for the Baltic pelagic ecosystem and the need to address the lack of quantitative information on their distribution and abundance have long been stressed by the Baltic Marine Environment Protection Commission’s Expert Group on Zooplankton (HELCOM EG Zoo) and several expert groups in ICES, in particular the working group on Integrated Assessment for the Baltic (ICES WGIAB).