Targeting the live market: Recovery of Norway lobsters Nephrops norvegicus (L.) from trawl-capture as assessed by stress-related parameters and nucleotide breakdown

The recovery potential of Norway lobsters (Nephrops norvegicus) held in on-board seawater tanks after trawl-capture was assessed at two different times of the year (winter and summer). Survival recorded 24 h after trawl-capture was 84.83 ± 0.93% in the winter compared to 75.35 ± 2.92% in the summer. Stress-related parameters in the muscle (arginine phosphate, glycogen and L-lactate) and in the haemolymph (L-lactate) were measured, together with nucleotide breakdown products in the muscle (yielding the “Adenylate Energy Charge” or AEC ratio). All parameters analysed were responsive to the stress of the trawl-capture and subsequently recovered towards resting values, but did so at different rates. The fact that some measures recovered at a faster rate than others should be taken into account when trying to develop an index of metabolic stress for this species. Animals trawled in the winter recovered to AEC values above 0.8 within 4 h of placing them in on-board seawater tanks, whereas animals trawled in the summer took 24 h to reach these values. Furthermore, at the end of the trials animals trawled in the summer presented significantly higher haemolymph L-lactate and lower muscle glycogen reserves than the animals trawled in the winter, suggesting a faster recovery in the winter compared to the summer. Finally, animals in the winter were better able to endure further stresses (an emersion of 1 h while animals were transported to the commercial handling facilities). Therefore, as a code of practice it is advised that trawled N. norvegicus directed to the live trade should be allowed to recover for at least 4–6 h in on-board tanks, and extra care should be taken especially in the summer, if further stresses such as additional emersion are to be applied within the first 24 h after capture.