Directe effecten van de visserij met 12m- en 4m-boomkorren op het bodemleven in de Nederlandse Sector van de Noordzee

Direct effects of trawling with commercial 12-m beam trawls on the abundance of benthic species in a soft bottom area in the southern North Sea were studied by comparing densities before and after trawling. Various sampling gears were used, including a benthos dredge (Triple-D) developed especially for this study. After trawling a study area twice, mortality could be estimated for a number of species. For fish species, mortality varied from 4% (small fish) to 75% (large fish) of the numbers initially present. Mortality exceded 100% for dab, Limanda limanda, as it rapidly immigrates into the trawled area already during trawling. For invertebrate species, mortality was variable as well, and estimated at 3-19% for echinoderms, 0-85% for molluscs, 4-74% for crustaceans, 1-56% for annelids, and 70% for anthozoans. Dab was a predominant scavenger on damaged or exposed fauna on the recently trawled seabed. The presence of infauna species in catches of the 12-m beam trawls indicated, that the sediment was disturbed by the tickler chains to a depth of approximately 2 to 4 cm.