Competition for the fish - fish extraction from the Baltic Sea by humans, aquatic mammals and birds

Populations of fish eating mammals (primarily seals) and birds have increased in the Baltic Sea and there is concern that their consumption reduces fish stocks and has negative impact on the fishery. Based primarily on published data on fisheries’ landings and abundances, consumption and diets of birds and seals around year 2010, we compare consumption of commercial fish species by seals (1*105 metric tons per year) and birds (1*105 tons) to the catch in the commercial and recreational fishery (7*105 tons), and when applicable at the geographical resolution of ICES subdivisions.

The large populations of herring (Clupea harengus), sprat (Sprattus sprattus) and cod (Gadus morhua), primarily inhabit off-shore areas and are mainly caught by the fishery. Predation by birds and mammals likely has little impact on these stocks. For these species, seals and birds may be negatively impacted by competition from the fishery.

In the central and southern Baltic, seals and birds consume about as much flatfish as is caught by the fishery and competition is possible. Birds and seals consume 2-3 times as much coastal fish as is caught in the fishery. Many of the coastal species are not much targeted by the fishery (e.g. eelpout Zoarces viviparus, roach Rutilus rutilus and ruffe Gymnocephalus cernua), while other species used by wildlife are important to the fishery (e.g. perch Perca fluviatilis and whitefish Coregonus spp.) and competition between wildlife and the fishery is likely, at least locally.

Estimated wildlife consumption of pike (Esox lucius), sea trout (Salmo trutta) and pikeperch (Sander lucioperca) varies among ICES subdivisions and the degree of competition for these species will likely differ among areas. Our results indicate that competition between wildlife and fisheries need to be addressed in basic ecosystem research, management and conservation.

This requires improved quantitative data on wildlife diets, abundances and fish production