| Summary: | No abstracts are to be cited without prior reference to the author. The interactions between cod (Gadus morhua), herring (Clupea harengus) and sprat (Sprattus sprattus) in the Baltic Sea were examined by simulation with a robust dynamic model, an alternative to more complicated and data-demanding multispecies models. The main targets of the study were to find out structural uncertainties of the system and sensitivity of the model output to key parameter values. The results were then compared to the predictions made with the forward calculating multispecies model used by ICES for fish stock assessment in the Baltic Sea. The model output was sensitive to the functional response in predation by cod on herring and sprat. The type II functional response led to a collapse of the clupeid stocks when cod was abundant, while the type III response produced more plausible stock dynamics. According to the simulation, an abundant cod stock was able to keep the sprat stock at a low level. Herring was less affected. The functional response was the most important source of differences in the results obtained with the dynamic model compared to the ICES multispecies model.
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