ABSTRACT: C Influences of fishery activities on herring gulls and great black-backed gulls (Larus argentatus, L. marinus) wintering on the island of Helgoland, south-eastern North Sea, were studied. When cod fishery discards were available close to the island, 83 to 87% of the gulls' pellets contained fishery discard remains and 70 to 73% of all pellets consisted exclusively of these. At times when no nearby trawling took place (Christmas/New Year), numbers of herring gulls dropped by up to 86% and numbers of great black-backed gulls by up to 80%. Similar declines were observed during a trawling moratorium in February 1998. Adults of both gull species had a significantly lower body mass during periods of no fishing around the island (13 and 24% less, respectively). Retraps of single gulls support these findings. The results show for the first time a strong influence of discard availability on numbers and body condition of large gulls wintering in the south-eastern North Sea. Effects on gull winter mortality and thus on population dynamics can be assumed.

KEY WORDS: Fisheries · Herring gull · Great black-backed gull · Resting numbers · Food · Fishery discards · Body condition · North Sea

Published in MEPS Vol. 194 (2000) on March 17
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 2000