MULTSPEC – a review of a multispecies modelling project for the Barents Sea

Abstract In the Barents Sea the yearly change in predation pressure from cod ( Gadus morhua ) on capelin ( Mallotus villosus ) may be of the same order of magnitude as the capelin fishery. The model MULTSPEC is used to study the species interactions quantitatively with the aim of improving the management of these species. The species undergo strong migrations throughout the year and the model is structured by seven areas and uses a one month time step in order to account for the time-varying overlap between the species. The species included are also structured by age, length and sex. The most immediate use of the model in a management context is to calculate the spawning stock biomass of capelin, which cannot be measured directly. This entity is nevertheless crucial for management of capelin, since it is believed that most capelin die after spawning and the stock is therefore managed with a constant escapement strategy. MULTSPEC is a forward simulation model using trawl-acoustic surveys as input data for the capelin stocks. For cod, where absolute stock abundance estimates from surveys are not available, VPA estimates are used. In co-operation with PINRO, Murmansk, Russia, a stomach content data base of 80 000 cod stomachs has been established, enabling a quantification of cod predation on other species. MULTSPEC has been parametrised for the mature capelin–cod subsystem and the model results are now in use in management of Barents Sea capelin. The model has also been used as a long-term simulation model for studying the impact of minke whales ( Balaenoptera acutorostrata ) and harp seals ( Phoca groenlandica ) on the cod, capelin and herring ( Clupea harengus ) stocks. The former use of the model has only partly been published in the primary literature. The latter use has been published, but is nevertheless reviewed here to give a full account of the MULTSPEC work in one paper. The aim of this paper is to give a qualitative overview of the modelling work and related results in a reference paper not burdened with excessive mathematical detail. The present and future uses of the model for the management of cod, capelin and herring are discussed.