Survival of decapod crustaceans discarded in the Nephrops fishery of the Clyde Sea area, Scotland

The Clyde Sea Nephrops fishery produces large amounts of invertebrate discards. Of these, as much as 89% are decapod crustaceans, including the swimming crab Liocarcinus depurator (Linnaeus, 1758), the squat lobster Munida rugosa (Fabricius, 1775) and the hermit crab Pagurus bernhardus (Linnaeus, 1758). The short-term mortality of these species was assessed following trawling and periods of aerial exposure on deck (16–90 min), and ranged from 2–25%, with Pagurus bernhardus showing the lowest mortality. Two experiments were performed to determine the longer-term survival of trawled decapods compared to those with experimentally ablated appendages. Deliberately damaged decapods had a significantly lower longer-term survival (ca. 30%) than controls (72–83%). Survival of trawled Liocarcinus depurator that had been induced to autotomize two appendages was slightly lower (74%) compared with intact creel-caught animals (92%). Mortality rates stabilised about 10 d after trawling. Our results suggest that post-trawling mortality of discarded decapod crustaceans has been underestimated in the past, owing to inadequate monitoring periods.