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

Herring fisheries are among the most important fisheries in the Baltic Sea both in terms of landing weight and economic value. In the Northern Baltic Sea, especially in the Gulf of Bothnia, the condition of adult herring (age 3 and more) has undergone a sudden drop in 2021, followed by a recovery from 2023 onwards. These shifts were concomitant with the quasi disappearance then recovery of Mysids and Limnocalanus macrurus in this area.

These shifts in the body condition of adult herrings contributed to driving the spawning stock biomass (SSB) of the Bothnian herring closer to the reference point Blim (value of the spawning biomass under which no fishing should take place), which had significant consequences on the catch advice. This situation underlined the importance of mysids for the Baltic pelagic ecosystem and the need to address the lack of quantitative information on their distribution and abundance.

This need for improved information on mysids has 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).

REMINDER will improve the understanding of mysid dynamics in the Baltic Sea and its effect on herring body condition and growth

1. Characterizing the distribution of the mysids, in space and in the water column:

This part of the work will improve the knowledge of the geographical and vertical distribution of mysids in the Baltic Sea, where the last significant information dates back to the late 1980’s and early 1990’s. It will therefore enable to identify possible shifts between past and current distributions

2. Characterizing the interaction between herrings and mysids:

This part of the work will improve and update the knowledge of (1) the variability of herring predation upon mysids in space and time and across size-groups, and (2) the influence of mysid (and other large crustacean zooplankton) abundance and distribution on herring distribution and behaviour.

3. Developing a quantitative mysid abundance index:

This part of the work will develop a protocol to provide a first quantitative index of the abundance of mysids and associated zooplankton in the Baltic Sea, based on the combined use of multifrequency echosounding data (SIMRAD EK80 fitted with 38, 120 and 200 kHz transducers) and direct zooplankton sampling by multinet and MIK net.

REMINDER is co-funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Maritime, Fisheries and Aquaculture Fund. Neither the European Union nor the granting authority can be held responsible for them.