Results and impact

In 2010 ? 2012 in the Archipelago Sea and Bothnian Sea area the diet of cormorant consisted of 29 fish species. In mass the most important diet items in biomass were perch, roach, viviparous blenny, Baltic herring in the Archipelago Sea and Baltic herring, ruffe, roach and perch. The diet varied temporally and spatially. The mean lengths of fishes consumed were: perch 15 cm, pikeperch 23 cm and roach 15 cm. The potential total loss of yield to fisheries in the Archipelago Sea, caused by cormorant feeding in one year (2010), was 100 - 130 tonnes for pikeperch and 310 - 390 tonnes for perch. The effect of cormorant presence on annual catches were estimated to 400 - 500 tonnes for perch and 70?90 tonnes for pikeperch, based on data from 2010 ? 2012. The catches of commercial and free-time fisheries have varied between 500 and 2 000 tonnes of perch between 225 and 525 tonnes of pikeperch in the 2000?s. Reliable information on the spatial and temporal composition of the diet of cormorants can be used when considering the management actions needed for solving the conservation-fisheries conflict.