Stress related physiological changes and post-release survival of Port Jackson sharks (Heterodontus portusjacksoni) and gummy sharks (Mustelus antarcticus) following gill-net and longline capture in captivity

Information on effects of fisheries capture on the physiology and post-release condition of sharks is urgently needed to design and implement effective fisheries management plans for shark stocks around the world, but obtaining data on post-release condition in the wild is very difficult. We used a controlled setting to subject Port Jackson sharks (Heterodontus portusjacksoni) and gummy sharks (Mustelus antarcticus) to varying durations of gill-net and longline capture stress for up to 360 min and monitored their condition via repeated blood sampling during a subsequent 72-h recovery period. Changes in plasma metabolites and electrolytes of Port Jackson sharks in response to our experimental treatment were small and no mortality was observed, suggesting that Port Jackson sharks are resilient to capture stress. In contrast, gummy sharks reacted very sensitively to capture stress, with severely disrupted acid–base and electrolyte balances, and immediate and delayed mortality was substantial (up to 70%) following gill-net capture. Moribund gummy sharks had very high plasma concentrations of lactate and potassium. Management measures for shark species that are susceptible to capture stress should aim to reduce the probability of interactions of that species with fishing gear.