Size-selective cod predation: impact on prey, implications for pelagic fisheries
We evaluated how size-selective cod predation influences the dynamics of sprat and herring in the Baltic Sea, as well as the competition with pelagic fisheries through immediate and delayed effects. We found a large overlap (30-60 %) between prey lengths targeted by cod and fisheries, which was largest in the 1974-1988 when cod had higher abundance and was larger in size. Cod generally consumes herring and sprat, which are smaller than those caught by the fisheries. This caused a delayed effect on prey biomass available for the fisheries, since smaller individuals that could have grown into harvestable sizes were consumed by cod. Estimated prey biomass unavailable for fisheries due to a delayed effect of cod consumption was estimated to be often similar to the biomass consumed in a size range suitable for the fisheries, essentially doubling the total potential effect of cod consumption.
Keywords: multi-species model, Baltic Sea, size-selective predation, competition with fisheries, mortality.