Diet of harbour seals and great cormorants in Limfjord, Denmark: interspecific competition and interaction with fishery

Comparative studies on seasonal and regional variation in the diet of harbour seals and great cormorants were conducted in Limfjord, a semi-closed water system in northwest Denmark. To compare harbour seal diet from an open water system containing similar prey species, a small diet analysis from the western Baltic is included. Seal diet during spring reflected the abundance of Atlantic herring entering Limfiord to spawn (90% of the weight consumed), whereas during summer and autumn, seal diet was rather more mixed. The diet of seals in the Rodsand area and cormorants in Limfjord showed no marked seasonal trends. During spring, there was little overlap between seal and cormorant diets in Limfiord because seals fed almost exclusively on Atlantic herring, and they consumed significantly larger herring than did the cormorants. During summer and autumn, seal and cormorant diets overlapped markedly, although the fish items consumed by seals were generally larger. Few commercially targeted species were found in the stomachs and scats of seals and casts of great cormorants, but Atlantic herring were taken by the seals at a size greater than that allowed by the fishery.