THE EFFECT OF SEDIMENT DREDGING ON THE DISTRIBUTION OF DIVING DUCKS AT LAKE MYVATN, ICELAND

Sediment dredging in Lake Myvatn, Iceland, which commenced in 1967, po ses a threat to the populations of breeding and moulting waterfowl in the area. Detailed mapping of diving ducks on the lake was carried out in order to evaluate the impact of the dredging. Densities of diving ducks in the dredged area were among the lowest in the lake. Positions of ducks diving for food were mapped in a 4-8-km2 area in the North B asin of the lake, which included the area disturbed by dredging. In Ju ne 1990 relatively few dives were recorded in the dredged area except by red-breasted mergansers Mergus serrator. In August numerous dives w ere recorded in the dredged area, yet they were significantly fewer th an outside, the area. The loss of habitat is still small in comparison with fluctuations which occur in the breeding populations, but dredgi ng in areas close to the present dredging activities will have a dispr oportionately large impact on the waterfowl populations.