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1 September 2012 Annual Variation in the Diet of Breeding European Shag (Phalacrocorax Aristotelis) in Central Norway
Grethe Hillersøy, Svein-Håkon Lorentsen
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The diet of breeding European Shag (Phalacrocamx aristotelis) was studied at Sklinna, one of the world's largest colonies, during 2007–2010. Regurgitated pellets were collected regularly throughout the chick rearing period and hard parts used to identify prey items to the lowest possible taxonomic level. The length and width of otoliths were used to estimate fish body length and mass. Shags' diet was varied and contained at least 17 different species of fish. Gadoid species, including saithe (Pollachius virens), cod (Gadus morhua) and Poor Cod (Trisopterus minutus), were the main prey and contributed approximately 90% of the diet during the study period. Saithe dominated the diet by numerical frequency, biomass and frequency of occurrence in all study years. Sandeels (Ammodytidae) contributed little to shag diet. The numerical frequency and percentage saithe biomass was lower in 2010 than in the other years. However, this was compensated by a higher frequency of cod and poor cod, making the total biomass of gadoids equal to previous years. The total biomass of gadoids caught by the shags at this colony was estimated at 340 metric tons, of which 266 tons were of 0–2 group saithe. The amount represents 0.1% of the total quota (by weight) for the fisheries and might, thus, be of minor importance for the fisheries. However, the estimated 30 million individuals represent 17% of the total number of individuals that was estimated to be recruited to the population as 3-year-old saithe in 2007–2010.

Grethe Hillersøy and Svein-Håkon Lorentsen "Annual Variation in the Diet of Breeding European Shag (Phalacrocorax Aristotelis) in Central Norway," Waterbirds 35(3), 420-429, (1 September 2012).
Received: 27 October 2011; Accepted: 13 February 2012; Published: 1 September 2012
Central Norway
European shag
gadoid fish
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