Interactions between fisheries and birds in IJsselmeer, The Netherlands

IJsselmeer, a eutrophic, shallow lake (mean depth 4 m) of 180,000 ha, is heavily exploited by a fishery that catches dfl 11 million worth of eel Anguilla anguilla , perch Perca fluviatilis , pikeperch Stizostedion lucioperca and of the small zooplanktivorous smelt Osmerus eperlanus, the main prey for perch and pikeperch and for the piscivorous birds of IJsselmeer. The population of cormorant Phalacrocorax carbo affects the fisheries through its predation on perch and pikeperch, whereas black tern Chlidonias niger and black-headed gull Larus ridibundus are affected by the availability of smelt in IJsselmeer. The spatial distribution of prey fish and piscivorous birds was described as a function of spatial scale, water transparency and water depth. The carrying capacity of IJsselmeer for the production of prey fish was assessed, and a dynamic simulation model was constructed to predict consequences of fishery management measures on the fisheries and on the food availability for piscivorous birds.