A NEW BENTHOS DREDGE (TRIPLE-D) FOR QUANTITATIVE SAMPLING OF INFAUNA SPECIES OF LOW ABUNDANCE

Grabs and corers are commonly used to estimate densities of infauna sp ecies quantitatively. However, because of the limited sample size, suc h instruments are not practicable for sampling species of low abundanc e. With trawls and dredges samples of much larger sizes can be obtaine d, but the existing types of gear are, at best, semi-quantitative for catching infauna. In this paper a prototype dredge is introduced for q uantitative sampling of larger-sized (> 10 mm) infauna of low abundanc e. This 'Deep Digging Dredge' (Triple-D) is rigged with an interchange able blade to collect a strip of the seabed. During the haul, several hundred metres long, the excavated sediment is sieved through a net wi th a 1.4 cm stretched mesh size. The prototype was successfully tested on infauna in fine-grained adhesive sediments in the Wadden Sea, usin g a 20-cm-wide blade with a penetration depth into the sediment of 10 cm. In field studies on soft and sandy bottoms in the North Sea, the T riple-D estimated the densities of some epifauna and flatfish species higher than a fine-meshed beamtrawl.