OCCURRENCE AND CONSUMPTION OF SEABIRDS SCAVENGING ON SHRIMP TRAWLER DISCARDS IN THE WADDEN SEA

Citation
U. Walter et Ph. Becker, OCCURRENCE AND CONSUMPTION OF SEABIRDS SCAVENGING ON SHRIMP TRAWLER DISCARDS IN THE WADDEN SEA, ICES journal of marine science, 54(4), 1997, pp. 684-694
Citations number
41
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Fisheries,"Marine & Freshwater Biology",Oceanografhy
Journal title
ISSN journal
1054-3139
Volume
54
Issue
4
Year of publication
1997
Pages
684 - 694
Database
ISI
SICI code
1054-3139(1997)54:4<684:OACOSS>2.0.ZU;2-O
Abstract
The fishery for the brown shrimp (Crangon crangon) on the coast of Ger many (Lower Saxony) produces a rich food source for ship-following sea birds. Large quantities of discarded fish and invertebrates attract fl ocks of gulls and terns. Between March 1993 and August 1994 the number and species composition of birds following two shrimp trawlers were d etermined. The main scavengers were herring gull (Larus argentatus) an d black-headed gull (L. ridibundus). Common gull (L. canus), lesser bl ack-backed gull (L. fuscus), great black-backed gull (L. marinus), and common/arctic tern (Sterna hirundolparadisaea) were less numerous. Th e distribution of scavenging seabirds behind the shrimp trawlers showe d a marked species-specific seasonal and spatial pattern. The scavengi ng behaviour of seabirds feeding on discards was studied by means of e xperimental discarding. Of 10 356 items offered, 8253 were picked up b y the birds. and in 8072 of these the consuming bird was identified. H erring gulls were most successful. Although this species represents on ly 45% of all birds counted, they took 82% of the total number of item s consumed. In total, ship-following seabirds consumed 41% of the offe red mass of flatfish, 79% of the roundfish, and 23% of four invertebra te species. In feeding experiments birds consumed 10% of undersized sh rimps. Applying these consumption rates and bioenergetic data to the t otal quantity of discarded biota, approximately 90 000 seabirds may be supported by this source throughout the entire fishing season (April- November 1993). Potentially, the discards of the shrimp trawler fleet of Lower Saxony were sufficient to meet the energy demand of 60 000 bi rds for the whole year. The results suggest that discards may have str ong effects on the bird populations and the ecosystem of the Wadden Se a. (C) 1997 International Council for the Exploration of the Sea.