Characterising the metabolic and stress physiology of the spanner crab (Ranina ranina): Increasing survivorship during live transport.

Australia has the largest commercial spanner crab (Ranina ranina) stocks, globally. Currently, only a small portion of the Australian catch is directed to the live export market. Although high value, the live export market remains difficult to supply, this is primarily due to delayed mortality syndrome (DMS), where individuals die several days post capture during the transport phase. Initial work by (Paterson et al. 1992) concluded that capture and handling methods used on spanner crab fishing boats were too stressful and were a direct driver of DMS.

Capture and transport in live crustacean fisheries typically involve several key stressors such as emersion, dehydration, fluctuation in temperature, hypoxia, noise, and vibration (Paterson and Spanoghe 1997; Stoner 2012; Powell et al. 2017). Despite Patterson’s early findings, capture, transport and holding procedures used in the fishery remained unchanged. Storage methods consist of keeping crabs packed in standard fish crates in a dry ice cooled storage hold. Consequently, the industry is unable to increase financial return and develop the live export market.

Several other live crustacean fisheries have developed techniques, employed post-capture, that increase and prolong survivorship through the transport chain (Barrento et al. 2011; Skudlarek 2011). Sedation techniques are commonly employed (Weineck et al. 2018; Whiteley and Taylor, 1992; Poole and Exley 2017). However, it remains untested if these treatments would be more effective if applied immediately post capture, onboard the spanner crab fishing vessel.

This study thus quantifies the metabolic response of spanner crab to two environmental variables that are common stressors in live crustacean fisheries. These stressors are water temperature and oxygen availability. This study used intermittent aquatic respirometry to measure the effect of temperature increase from 14.14°C to 18.49°C on the routine metabolic rate (RMR) of spanner crab and calculate the temperature coefficient (Q10). Mean RMR increased by 23% with the temperature increase and Q10 for this temperature range was 1.61. Closed aquatic respirometry was also employed to quantify hypoxia tolerance (O2crit) in spanner crab at the lower and upper temperature. The spanner crab O2crit at 18.49°C (57.02%) was substantially higher than the O2crit at 14.14°C (19.68%).

Furthermore, a quantitative field evaluation of sedation was undertaken to determine the efficacy of sedation techniques aimed at increasing survivorship and reducing stress in live animals. These techniques were applied to sedate animals landed onboard fishing vessels as early as possible in the capture-transport chain. Sedation techniques evaluated are cold water stunning (8°C for 10 min) and the commercially available aquatic isoeugenol anaesthetic AQUI-S (100ppm for 10 min). Performance of sedation techniques was assessed using biochemical analysis of haemolymph samples taken at temporal sample points post capture/treatment (1h, 3h, 6h, 12h, 24h, 38h) and survivorship was recorded up to 86 hours post capture/treatment. Analytes include Haemolymph L-Lactate, Glucose, pH and Ammonia concentration. The fishing control group had a survivorship of 46.67% at 86h whereas the AQUI-S and cold stun treatments had survivorships of 40% and 80%, respectively. The cold stun treatment group had the lowest mean haemolymph L-Lactate and ammonia concentrations at the 38h sample point and was the least acidic when compared to the AQUI-S treatment and the fishing control group. Ultimately, the output of this study aims to provide insightful information on the species’ stress physiology and possible offshore practices that promote survivorship in the fishery. This study aimed to further our understanding of the effect of temperature and hypoxic conditions on spanner crab aerobic metabolism. Furthermore, the study aimed to characterize the physiological stress response of spanner crab during the capture-transport phase and how this stress response may be mitigated by introducing established sedation techniques directly after capture. Refer to Appendix E for studies related to commercially important crustaceans and relevant to the thesis subject topic.