Assessing barotrauma and release methods among angled snapper (Pagrus auratus) and the utility of release methods

Australian recreational and commercial fishers catch snapper (Pagrus auratus) from down to ~120 m, often evoking barotrauma. Owing to minimum legal sizes and quotas or non-consumptive fishing practices, some afflicted fish are released, raising concerns over the potential for unaccounted fishing mortality. Two experiments were completed to quantify the (1) clinical signs of barotrauma among fish angled from 6 to 120 m (experiment 1) and (2) mortality (over 3 d) of fish with barotrauma that were released following either no treatment, venting (e.g. needle) or recompression (e.g. release weight) (experiment 2). In experiment 1, barotrauma was evident in some fish angled from 11 m and all from >20 m. Fish were considered to have barotrauma if they had a prolapsed cloaca combined with a distended coelomic cavity and/or gastric herniation into the buccal cavity. Despite similar clinical signs among fish in experiment 2, none died, however, the associated trauma raises welfare concerns. Both recompression and venting offered benefits over no treatment by returning fish to depth quickly and releasing gases, respectively. Nevertheless, the release method should be dictated by the clinical signs of barotrauma and extrinsic conditions, including the competency of the fisher (e.g. for venting), presence of predators (e.g. for recompression), and exposure to sun or warm water (e.g. no treatment). More selective gears, spatial and temporal closures, or possibly replacing minimum legal sizes with quotas in deep water only could also reduce the frequency of barotrauma among released P. auratus and therefore, negative impacts on stocks.