DISTRIBUTION OF SHIP-FOLLOWING SEABIRDS AND THEIR UTILIZATION OF DISCARDS IN THE NORTH-SEA IN SUMMER

Prey availability is one of the factors determining the distribution of seabirds at sea. Northern fulmars Fulmarus glacialis and black-legged kittiwakes Rissa tridactyla were the most regular and frequent ship-followers across the central and northern North Sea during 2 surveys with a fishery research vessel in May-June and July-August 1992. Sixteen other species occurred less often and/or in lower numbers. Birds consumed 84% of experimentally discarded roundfish and 8% of discarded flatfish. On average, northern gannets Morus bassanus took the largest individuals of most fish species, black-legged kittiwakes the smallest. The average size choices of herring gulls Larus argentatus, lesser black-backed gulls Larus fuscus and northern fulmars lay between these 2 extremes. The choice of fish lengths by birds varied with different fish species. Northern gannet was the most successful species in consuming discards. Northern fulmars' success rates decreased with the presence of larger ship-followers but were never high. Black-headed gull Larus ridibundus and common gull Larus canus were less successful than the more frequent, typical ship-following species.