Scavenging seabirds at beamtrawlers in the southern North Sea: distribution, relative abundance, behaviour, prey selection, feeding efficiency, kleptoparasitism and the possible effects of the establishment of 'protected areas'
Camphuysen, C.J. (1994). Scavenging seabirds at beamtrawlers in the southern North Sea: distribution, relative abundance, behaviour, prey selection, feeding efficiency, kleptoparasitism and the possible effects of the establishment of 'protected areas'. BEON Rapport = BEON-report(14). NIOZ: Texel. 47 pp.
Part of: BEON Rapport = BEON-report. Programma Bureau BEON: Den Haag. ISSN 0924-6576
At least 28 species of seabirds have been observed as scavengers associated with commercial trawlers in the southern North Sea. The most important consumers of discards and offall in the southern North Sea are Fulmar, Gannet, Blackheaded Gull, Common Gull, Herring Gull, Lesser Black-backed Gulls, Great Black-backed Gulls and Kittiwake. In the breeding season, internationally important numbers of Herring Guls (2.8% of the NE Atlantic population) and Lesser Black-backed Gulls (12.9%) were found in the Dutch sector of the North Sea. Of these, 23.9% and 41.9% respectively were found within the sector proposed for protection bordering the Wadden Sea island. In Dutch beamtrawl fisheries, the most important fishery in the area, large amounts of discards, benthic invertebrates and offall are discharged. An estimated 5-10kg of flatfish (45-50%), roundfish (1-5%) and benthic invertebrates (45-50%) were discarded per kg landed, marketable fish. All the offall and virtually all fish were suitable for consumption by seabirds. The proportion (%) of discards, offall and benthic invertebrates consumed by seabirds amounted to 87% in roundfish, 82% in offall, 28% in flatfish and less than 1% in benthic invertebrates. Of seabirds breeding in the Netherlands, only Herring gull and Lesser Black-backed Gulls profited from discards and offall to a large extent. The first was only found at inshore trawlers, the latter had a larger feeding range at sea. The establishment of 'protected areas', closed for fisheries, off the Dutch Wadden Sea islands (as proposed in Bergman et al. 1991) will probably only negatively affect the foraging possibilities of Lesser Black-backed Gull, particularly the breeding poulation on Texel, Vlieland and Terschelling (ca. 50% of the Dutch population). Reductions in the amount of discards and offall produced in commercial fisheries will affect the feeding possibilities of the seabirds in different ways, depending on the way in wich reductions are achieved. Increased mesh size, less fishing days or fleet reduction, reductions of fisheries in the coastal zone or a total ban of fishing in certain areas will have effects that can roughly be predicted from data derived from this study. Future research will have to focus on the relative importance of pelagic fish for breeding birds feeding in the coastal zone, particularly on the relationship between breeding and the provision of chicks with discards and/or pelagic fish.
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