Vissende vogels achter het net

Scavenging seabirds behind trawlers are a well known but relatively little studied feature. The negative side-effects of fisheries, including fish stock depletion and damage to benthic communities, have been discussed thoroughly during the last few decades but particularly seabirds have also profited from commercial fisheries, exploiting discarded fish and offal. Dutch governmental plans to close a sea area off Texel and Vlieland for all fisheries may have a significant effect on the breeding success of gulls breeding on these two islands and on Terschelling. If this plan is to be realized, it could possibly lead to drastic population declines in the area. In a new study, which commenced in August 1992 at the Netherlands Institute for Sea Research on Texel, the significance of discards from commercial fisheries for scavenging seabirds in the southern North Sea will be studied. In a first analysis of data collected at sea during 1987-1992 (NIOZ and DGW/NZG data), species, age composition, spatial and temporal distribution of scavengers behind trawlers on the Dutch sector were studied, using records of 461 trawlers (figure 1). An example of a result is given in figure 2, where the presence of Common Gulls Larus canus behind trawlers in summer and winter is plotted on a map. The example shows a species which is virtually absent during the breeding season, but which is quite important as a scavenger in the coastal zone in winter. In order to obtain more data, a system is developed for the registration of fishing vessels and associated seabirds, to be used on board vessels during surveys of seabirds at sea, or by seawatchers on coastal sites.