Cormorants Phalacrocorax carbo sinensis in shallow eutrophic freshwater lakes: Prey choice and fish consumption in the non-breeding period and effects of large-scale fish removal.

During the period October 1989-April 1992 a study on Cormorant feeding ecology was carried out in two shallow lakes in The Netherlands: lake Veluwemeer and lake Wolderwijd (3240 and 2600 ha respectively). Increasing numbers of Cormorants use these lakes for feeding in the non-breeding season; the maximum number, usually reached in October or November, amounted to 1314 in 1991. The effect of Cormorant predation on fish stock was studied for two reasons: assessing possible damage to commercial fishery and assessing the role of the birds in a large-scale biological management programme that has been carried out in lake Wolderwijd during the period of study. As part of this programme, fish stock in this lake was reduced from 203 to 46 kg/ha. Most important prey species was Ruffe (60% of fish-mass in 1991/92), which has no value to either commercial fishermen or anglers.

Dirksen S., Boudewijn T.J., Noordhuis R. & Marteijn E.C.L., ARDEA 83 (1): 167-184.