Mortality of Asterias rubens and Ophiura ophiura discarded in the Nephropsfishery of the Clyde Sea area, Scotland

The Clyde Sea Nephrops fishery produces large amounts of invertebrate disca rds. Of these, up to 80%, (by numbers) are echinoderms. including the starf ish Asterias rubens and the brittlestar Ophiura ophiura. The short- and lon ger-term mortality of these species was determined after trawling in order to gain reliable estimates of trawl-induced mortality. Short-term mortality was assessed after trawling and periods of aerial exposure on deck, and ra nged from 0-31%, with A. rubens showing lower mortality. Mortality of hapha zardly collected echinoderms of Various sires and degrees of damage was mon itored over one month to determine longer-term mortality. The effects of in jury on starfish survival were also examined, as were the effects of trawli ng and aerial exposure on O. ophiura survivai and A. rubens righting time. Injured A. rubens had a significantly higher long-term mortality (22-96%) t han controls (4%). Trawling and aerial exposure significantly increased rig hting times of A.. rubens. implying susceptibility to stress and an increas ed risk of predation. Moribund A. rubens developed white lesions containing bacteria (Vibro metschnikovii and Acinetobacter sp.) and mortality rates o nly stabilised in the third week after trawling. In contrast all trawled O. ophiura died within 14 d. Immediate re-immersion in sea water resulted in lower, but nevertheless high, mortality (91%). Our results suggest that pos t-trawling mortality of discarded echinoderms has barn underestimated in th e past. (C) 2001 International Council for the Exploration of the Sea.