Cormorant diet in relation to temporal changes in fish communities

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Abstract

The stomach contents of 229 great cormorants (Phalacrocorax carbo sinensis) shot between March and October 2009 along the Swedish east coast were analysed for differences in diet between gender, age, and breeding phase. Sticklebacks (Gasterosteus aculeatus and Pungitius pungitius) were the most common prey, followed by eelpout (Zoarces viviparus), herring (Clupea harengus membras), and cyprinids (Cyprinidae). Diet did not differ between age and gender, but changed over the breeding season. The different phases explained around 10% of the total variation in stomach content between cormorants, suggesting no major shift in diet over the breeding season. The diet of cormorants in 2009 was compared with the results of a study conducted in the same area in 1992. There were evident changes in the diet between 1992 and 2009, with less perch (Perca fluviatilis) and cyprinids and more eelpout and herring in 2009. This change in diet could partly be related to changes in the fish community. The seasonal changes in diet composition of whole stomachs were less notable than in many previous studies, but long-term changes in the fish communities may induce changes in cormorant diet. It is clearly important to use stomach contents in areas with many small fish species for a comprehensive assessment of cormorant diet.

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