Physiological changes in the Norway lobster Nephrops norvegicus (L.) escaping and discarded from commercial trawls on the West Coast of Scotland -: II.: Disturbances in haemolymph respiratory gases, tissue metabolites and swimming performance after capture and during recovery

The physiological states of trawled and creel-caught (control) Norway Lobsters (Nephrops norvegicus (L.)) captured on grounds off the West Coast of Scotland (120-150 m) were compared. Undersized discards (< 25-35 mm carapace length) were sampled directly from the cod-end and following recovery in underwater (u/w) cages at a mean depth of 24 m. Escaped animals which had passed through the cod-end meshes and collected in a small-meshed net cover were transferred without emersion (air-exposure) for sampling on-board. Some of these individuals were also transferred by SCUBA divers to u/w cages. Haemolymph PO2, PCO2 and pH measurements showed that both discarded and escaped animals experienced moderate internal hypoxia, hypercapnia and acidosis which became severe after 1 h emersion of the former on deck. A marked handling effect was evident in which haemolymph PO2 declined and PCO2 became elevated in both controls and recovering trawled animals. In both discarded and escaped animals haemolymph L-lactate and D-glucose concentrations were high compared to controls, but with levels significantly lower in escapes suggesting less tail-flip swimming activity within the cod-end cover. Further emersion had little effect on haemolymph L-lactate in discards. Recovery to control levels of both metabolites occurred within 24 h in u/w cages but the exercising of captured individuals (by tactile stimulation) produced further significant increases. Abdominal flexor muscle concentrations of L-lactate were also elevated in discards and escapes and positively correlated with haemolymph levels. Muscle glycogen showed severe depletion in both groups compared to unexercised controls and 1 h emersion reduced levels drastically (to similar to 20% of normal concentrations). High haemolymph ammonia (T-amm) was characteristic of both trawled groups but was reduced rapidly during recovery. These metabolite changes were accompanied by reductions in the number of escape swimming tail-flips that could be elicited before exhaustion, particularly in discards. This reduction in performance was evident in discards even after 24 h recovery, but escapes showed almost normal responses. The severity of the physiological stresses experienced during trawling, and to a lesser extent in escaped animals, and their effects on recovery of undersized discards regaining the seabed, is discussed. These findings may help us predict the survival, longer-term recovery and fitness of fished N. norvegicus, and their potential contribution to the regeneration of exploited populations. (c) 2005 Elsevier B.V. All rights reserved.