Cormorant predation – a potential threat to coastal fish populations

The European population of Great cormorant (Phalacocorax carbo sinensis) has increased from few thousand pairs in 1980 to app. 300,000 now, equalling more than one million individuals. The number of cormorants foraging in the Danish waters vary from 15,000 in mid-winter to 250,000 in the fall. Each bird eats on average 500g of fish daily, so the birds’ annual consumption is app 16,000 tonnes. Cormorants eat fish of almost all species in all sizes up to 1.5 kg and is an efficient hunter in streams, rivers, lakes, fjords and open coast and forage in few cm water to 50 meters depth. In fresh water, the predation from cormorants have been documented to have a severe negative impact, especially on stationary river fish species, even on healthy, natural populations in habitats of high ecological quality. Recently, the apparent collapse of coastal fish populations, have revived focus on the role of “natural predation” and older research and data indicate that the predation from cormorants may indeed be high on fish like flounder and cod along Danish coasts. DTU-Aqua initiated a pilot study to look closer to this and the results from this PIT-tagging study point to predation being important. In this presentation, the background of conflict between cormorant conservation and fishery interest and fish conservation is discussed and the relevant research so far is presented.