The impact of water jet dredging for razor clams, Ensis spp., in a shallowsandy subtidal environment

The effects of water jet dredging for Ensis spp, on the seabed and benthos were examined through experimental fishing. Immediate physical effects were apparent, with the dredge leaving visible trenches in the seabed. While th ese trenches had started to fill after five days, and were no longer visibl e after 11 weeks, the sediment in fished tracks remained fluidised beyond t his period. The majority of the studied infaunal community is adapted morph ologically and behaviourally to a dynamic environment, and other than initi al removal through dispersal, is not greatly affected by the dredge at the site studied. Species that are likely to be affected (e.g. the heart urchin Echinocarium cordatum, Arctica islandica and other large bivalves) were ve ry rare in infaunal samples, but present in dredge catches, where damage wa s noted, and ranged on average from 10 to 28% of individuals. Epifauna were scarce in the study area, and unaffected by the fishing, except that epifa unal scavenging species were attracted to the fished tracks. On the evidenc e of the present and previous studies, it would appear that there was littl e difference between the biological impact of hydraulic and suction dredgin g, although the latter may have a greater physical effect (larger trenches) . Crown copyright (C) 2000 Published by Elsevier Science B.V. All rights re served.