Validation of a vigour index for trawl-caught Norway lobsters (Nephrops norvegicus) destined for the live market: underlying links to both physiological condition and survivability

Abstract

Recent improved practices in the trawl fishery of Norway lobsters (Nephrops norvegicus) have made it possible to increase the proportion of these trawl-caught lobsters that can be transported alive successfully. A major contributor to this has been the introduction of on-board seawater tanks, which allow for the recovery of animals immediately after they have been landed from the net. In this study, we have validated a vigour index that could be used both by by fisheries scientists and the industry dealing with live-traded Nephrops to screen out the proportion of trawl-caught lobsters that nevertheless fail to recover following capture and are not in a condition to survive live transportation. Results indicate that the process of visual selection into one of four possible vigour categories reflects with good accuracy the underlying physiological state of the animals, as assessed by the level of adenylate 5’ -triphosphate (ATP) in the tail muscles, by the proportions of other nucleotides as expressed in the Adenylate Energy Charge (AEC), and by the amount of intra-muscular L-lactate present. The vigour index also correlates well with their subsequent survival potential in a semi-dry transport system.