Great cormorant diet data from the Norwegian coast ...

• Main Authors: Dehnhard, Nina, Langset, Magdalene, Aglen, Asgeir, Lorentsen, Svein-Håkon, Anker-Nilssen, Tycho
• Format: Dataset
• Language: English
• Published: Dryad 2021
• Subjects: FOS Biological sciences; Frøya; Lofoten; Norwegian Sea; Røst; Sklinna; Gadus morhua
• Online Access: https://dx.doi.org/10.5061/dryad.b5mkkwhcd; https://datadryad.org/stash/dataset/doi:10.5061/dryad.b5mkkwhcd

Piscivorous wildlife is often perceived as competitors by humans. Great cormorants of the continental subspecies (Phalacrocorax carbo sinensis) in the Baltic and North Sea increase, while local cod (Gadus morhua) stocks decline. In contrast, numbers of the Atlantic subspecies (P. c. carbo), breeding along the Norwegian and Barents Seas have been relatively stable. We investigated the diet of both great cormorant subspecies in breeding colonies along the Norwegian Coast from Lofoten to the Skagerrak and estimated the biomass of fish consumed annually by great cormorants in Norwegian waters. The birds’ consumption was compared with estimated fish stock sizes and fishery catches. Cod and saithe (Pollachius virens) 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 < 1.7% of estimated fish stocks and < 9% of that of human catches and therefore considered minor. Cormorant consumption of wrasses ... : Data collection Diet samples were collected between 2001 and 2016 from breeding colonies at five different sites spread along the Norwegian coastline (Table 1, Fig. 1): Røst (67.5° N, 12.0° E), Sklinna (65.2°N, 10.9° E), Frøya (63.8° N, 8.5°E), Rauna (58.1° N, 6.7° E) and Øra (59.2° N, 11.0° E). Røst, Sklinna and Frøya are breeding sites of the Atlantic subspecies, whereas Rauna and Øra hold the continental subspecies. Diet samples consisted of pellets, i.e. indigestible material that is regurgitated daily as a natural part of the digestive process. All samples were collected from the vicinity of nests, thus presumed to originate from breeding adults either directly or via their chicks. After collection, they were stored frozen until being analysed. Analyses of diet samples The treatment of the pellets followed previous work by Hillersøy and Lorentsen (2012). Soft parts were digested in a saturated solution of biological washing powder (Bio-tex®) kept at 50°C in an oven for 1−2 days. Fish otoliths were ...