Multispecies considerations for the central Baltic stocks: cod in Subdivisions 25–32, herring in Subdivisions 25–29 and 32, and sprat in Subdivisions 22–32
ICES intends to provide multispecies advice on fisheries for some ecosystems (see Section 1.2) and encourages managers to apply such an approach to the central Baltic Sea. The present section may serve as a starting point for a dialogue between ICES and managers to foster the development of a multispecies management system for the Baltic. This text uses implicit management objectives and risk tolerance that need to be validated by managers. If managers decide to adopt a multispecies management approach a transition period from the present management will be required. As this work is mostly illustrative, ICES focuses on the most obvious interactions between commercially exploited fish stocks in the area and does not attempt to provide a full foodweb model.
The main result of the present preliminary quantitative multispecies analysis for the central Baltic Sea (Subdivisions 25–29 and 32 excl. Gulf of Riga) is that, compared to the present single-species approach, it could be possible to increase the sum of the sustainable yields in tonnes of the three species combined; the growth of individual fish would be improved if multispecies interactions were taken into account when setting target Fs. However, cod yields will remain about the same, whereas the probability of low cod spawning-stock biomass (SSB) will increase. Multispecies considerations indicate a multitude of solutions, all being biologically sustainable. The societal choice between these must be based on social and economic considerations and informed by social and economic impact assessments.
These results are derived assuming that there is full spatial overlap for all three stocks. The geographical overlap of cod and clupeid stocks is currently small, with cod found mainly in the south (Subdivision 25) and clupeids in the north (Subdivisions 28–29 and 32)
Published under the auspices of the following ICES Steering Group or Committee