Impact of scallop dredging on benthic megafauna: a comparison of damage levels in captured and non-captured organisms

The impact of scallop dredging on benthic megafauna was assessed by direct observation of damage, both in the bycatch and in organisms encountering dr edges but not captured. Damage was assessed using a simple 4-point scale ad apted for different taxonomic groups. Experimental dredging was undertaken on a scallop fishing ground in the north Irish Sea, off the Isle of Man. Di vers were deployed immediately after dredges had passed, to record levels o f damage to megafauna left in the dredge tracks. Mean damage levels, and th e proportions of the 4 damage scores in the bycatch and on the seabed, were the same in most species. Some common species did show differences. The ed ible crab Cancer pagurus was more severely damaged when not captured, while the starfish Asterias rubens and whelk Neptunea antiqua received greater d amage within the bycatch. Capture efficiency for the megafauna was low, ran ging from 2 to 25 % among species. The results indicate that the majority o f damage to large benthic invertebrates during scallop dredging occurs unob served on the seabed, rather than in the bycatch.