Net-entrapment of great cormorants Phalacrocorax carbo sinensis in relation to individual age and population size

Great Cormorant (Phalacrocorax carbo) Science Article 8


Population control of great cormorants Phalacrocorax carbo sinensis has beensuggested as a tool to mitigate fish losses by cormorants foraging in pound nets,gill nets and fykes. The objective of our study was to quantify the differencebetween first-year birds and older birds in the risk of drowning in fishing gear,and to explore the influence of population size on the proportion of individualsdrowning. An index of the proportion of first-year birds and older birds thatdrowned was obtained for cormorants ringed in the Danish Vorso colony usingresightings of colour-ringed individuals and ring recoveries of individuals founddead. First-year birds were approximately 10 times more likely to drown thanolder birds. We used ring recoveries of cormorants ringed in Denmark and founddead in Denmark, North Germany and South Sweden (i.e. in the main postbreedingarea) to reveal changes over a 25-year period in the proportion drownedamong those recovered.

Thomas Bregnballe & Morten Frederiksen, Wildl. Biol. 12: 143-150.

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