A multispecies model of fish stocks in the Baltic Sea

The Andersen and Ursin multispecies stock assessment model has been slightly modified and used to simulate interactions between cod, herrings, sprat, benthos and zooplankton in sub-divisions 2S-29S of the Baltic in the years 1974-1984. The main modifications were: including intraspecific competition into the feeding level formula and introducing a prey biomass-dependent preference index. The model has been verified by comparing simulated yield, age at catch, growth of fish, and cod food composition with appropriate observed values. Finally, a number of fishing strategies where fishing mortality and age at full capture of cod were changed under the simulations.