In early March this year, a group of fisheries scientists, representatives from the Baltic Sea RAC and policy makers gathered in Charlottenlund, Denmark to discuss the possibilities of instituting multispecies advice for the Baltic. The current workshop, WKMULTBAL, was a follow up meeting to a workshop held at ICES headquarters in December last year.
As of this year, ICES will provide scientific advice for quotas in the Baltic Sea within the multispecies approach, while also continuing to give advice in accordance with single-species models. Decisions on quotas for the Baltic will be decided at the October Council meeting.
An ecosystems approach to fisheries management, that accounts for species interactions and environmental factors, has long been a highly prioritised goal of the ICES working groups. The implementation has been delayed due to the complexity of such interactions.
ICES did however decide that if such a multispecies approach would come to be implemented, it would, first be applied to the eastern Baltic Sea since the complexity of species interactions is relatively low (the bulk of fish biomass is cod, sprat and herring) and the knowledge base is fairly high compared to, for example, the North Sea which is considerably more multifaceted.
The purpose of the working group was to present a series of simulation runs from current multispecies models and identify possible pitfalls. It was appreciated that the models were in need of some revision before advice on such grounds could come to be implemented. In particular, concerns were made regarding the different degrees of species interactions in different areas of the Baltic.
Since the majority of the cod stock is concentrated in the central Baltic proper, interactions between cod, herring and sprat would be particularly strong in that area, in comparison to the northern Baltic for instance where the principal interaction would be between sprat and herring only. There was a consensus in the group that accounting for this bias would improve the model substantially.
Furthermore, because a multispecies model produces values of fishing mortality that are conditional on each other, in contrast to the current single species approach, it was also recommended that a series of scenarios where fishing mortality is allowed to vary among the species (within precautionary levels) would be presented to decision makers. This would enable them to adjust species specific quotas to area specific fisheries management plans. It was also stressed that ecosystem consequences outside the framework of the model would have to be considered in any advice that is given. For instance, too high cod biomass could lead to depleted food supplies for seals and harbour porpoises which would go against other environmental objectives.
The meeting concluded that the model was in need of considerable modifications and that multispecies advice could not be presented. ICES aims to have reliable results for the coming Scientific, Technical and Economic Committee for Fisheries (STECF) meeting in Rostock at the end of March.