Abstract
The occurrence of scavenger seabirds at fishing trawlers was studied off Galicia, Spain. A total of 9,368 seabirds of 23 species were recorded during 92 fishing operations in 1998 and 1999. The most common species were the yellow-legged and lesser black-backed gull ( Larus cachinnans and L. fuscus ), Sabine´s gull ( L. sabini ), the northern gannet ( Morus bassanus ), the great shearwater ( Puffinus gravis ), sooty shearwater (P. griseus), the Manx and Balearic shearwater ( P. puffinus and P. mauretanicus ), the great skua ( Catharacta skua ) and terns (mainly Sterna hirundo and S. paradisaea ). Other species occurred in small numbers: Leach´s petrel ( Oceanodroma leucorhoa ), the storm petrel ( Hydrobates pelagicus ), the little shearwater ( Puffinus assimilis ), Cory´s shearwater ( Calonectris diomedea ), the parasitic skua ( Stercorarius parasiticus ), the pomarine skua ( S. pomarinus ), the black-headed gull ( Larus ridibundus ), the glaucous gull ( L. hyperboreus ), the kittiwake ( Rissa tridactyla ), the sandwich tern (Sterna sandvicensis), the black tern (Chlidonias niger), the guillemot ( Uria aalge ) and the little auk ( Alle alle ). The maximum number of seabirds recorded at a haul was 320. The maximum number of a particular species ranged from 120 great shearwaters to 250 yellow-legged/lesser black-backed gulls during a single haul. The differences in ship-follower species abundance are related to migratory movements but fisheries could also have a strong influence at a smaller scale on the distribution of seabirds off Galicia. The degree to which seabirds rely on fishery discards as food was not quantified, but may be important for several species.
Highlights
Many species of seabirds feed offshore and profit from fisheries discards and offal
Fisheries have a considerable influence at several scales on the distribution of seabirds at sea due to availability of discards as food for scavenging species (Camphuysen et al, 1995; Furness, 2000)
Most studies in European waters have been in the North Sea (Furness et al, 1992; Garthe and Hüppop, 1994; Camphuysen et al, 1995)
Summary
Many species of seabirds feed offshore and profit from fisheries discards and offal. Large feeding flocks follow fishing vessels, with spatial and temporal variations in species composition and hierarchy among the scavenging seabirds attending. Fisheries have a considerable influence at several scales on the distribution of seabirds at sea due to availability of discards as food for scavenging species (Camphuysen et al, 1995; Furness, 2000). The populations of several species have grown considerably in the last few decades, probably partly as a result of improved food resources provided by fisheries (Tasker et al, 2000). In the Mediterranean, the effects of changes in fishing activity on seabird populations have been studied and clearly shown for some species such as the rare Audouin’s gull (Larus audounii) (Oro, 1996; Oro et al, 1996: Arcos, 2001)
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