Great cormorant diet data from the Norwegian coast

<p>Piscivorous wildlife is often perceived as competitors by humans. Great cormorants of the continental subspecies (<i>Phalacrocorax carbo sinensis</i>) in the Baltic and North Sea increase, while local cod (<i>Gadus morhua</i>) stocks decline. In contrast, numbers of the Atlantic subspecies (<i>P. c. carbo</i>), breeding along the Norwegian and Barents Seas have been relatively stable.</p> <p>We investigated the diet of both great cormorant subspecies in breeding colonies along the Norwegian Coast from Lofoten to the Skagerrak and estimated <a name="_Hlk42867405">the biomass of fish consumed annually by great cormorants in Norwegian waters. </a>The birds' consumption was compared with estimated fish stock sizes and fishery catches.</p> <p>Cod and saithe (<i>Pollachius virens</i>) dominated the diet in the Norwegian Sea, and wrasses  in the North Sea and Skagerrak. Estimated total fish consumption of cod and saithe by great cormorants was &lt; 1.7% of estimated fish stocks and &lt; 9% of that of human catches and therefore considered minor. Cormorant consumption of wrasses amounted to 110% of human catches.</p> <p>The practice of using wrasses as cleaner fish in the salmon farming industry leads to a conflict with cormorants, and we urge for a better understanding and management of wrasse populations, taking ecosystem functioning and natural predation into account.</p>