Multispecies reference points for a three species system with a predator and two prey species in the Baltic Sea

No abstracts are to be cited without prior reference to the author.

Studies have shown that maximizing the total yield in a multispecies system isn’t desirable since it will enforce fishing solely on the lowest trophic levels (Gislason, 1999). An economic maximal yield can benefit the inclusion of top predatory species in the catches, but is with variable fish market values difficult to analyze . An alternative approach is of the aggregate surplus production models in mixed fisheries (Fogarty et al. 2012). We have developed a method to calculate the integrated reference points for three species via an analysis of the spawning stock biomasses at maximum sustainable yields (BMSY). The model is parameterized to describe the Baltic Sea with only three species constituting the main resources for the fisheries; cod Gadus morhua, herring Clupea harengus and sprat Sprattus sprattus. By analyzing how the BMSYs vary for different abundances of prey and predator we find a point where each species produces maximum sustainable yields (MSY) given the spawning stock biomass (BMSY) of the other species. This approach maintains the productivity on both trophic levels.