Seabed photography, environmental assessment and evidence for deep-water trawling on the continental margin west of the Hebrides

A photographic survey in 1998 of the seabed along depth transects from 700 to 1300 m across the N.E. Atlantic continental slope off north-west Scotlan d shows clear depth-related change in sediment type and megabenthic communi ty in an environment where biological communities and species distributions are poorly known. Small-scale features, such as trawl marks and dense fiel ds of xenophyophores, were resolved that may have remained unknown using co nventional sampling or lower resolution imaging techniques. Because xenophy ophores accumulate barite, a constituent of some drilling muds, their local -scale occurrences will be important to baseline environmental survey prior to hydrocarbon prospecting in deep water. Our results indicate that deep-s ea trawling is physically impacting the seabed to depths of more than 1000 m. The persistence and biological consequence of this impact is unknown, bu t may depend on sediment type and natural physical disturbance. Comparison with similar seabed photographs taken from a neighbouring area in 1988, whi ch show a high incidence of trawl marks, indicates that such impacts have b een taking place over at least 10 years.