Maximising the survival of bycatch released from commercial estuarine fishing gears in New South Wales

Abstract

In addition to the targeted catches, commercial fishers commonly catch other unwanted organisms (collectively termed 'bycatch') that are then discarded. Combined with the process of capture, such discarding may cause harm to individuals and ultimately affect entire populations. In response to concerns over such negative impacts, the aims of this study were to: (1) identify key factors and quantify their effect on the fate of key discards from seines, trawls, and gill nets used in southeastern Australian estuaries; and (2) test the utility of a range of operational and post-capture handling modifications designed to maximise survival. Five manipulative field (in the Wallis Lake and Clarence River estuaries), and two laboratory experiments (in Coffs Harbour) were completed to measure the effects of the deployment duration, configuration, and entanglement of gears, and air exposure on the stress, damage, and immediate and short-term mortality of discarded penaeids and teleosts. In the field, a total of 112 deployments were completed, with 21 species assessed for their post-capture condition. A random sub-sample of 5 950 penaeids was retained, and immediate mortalities of 81 589 teleosts landed on deck were determined, before representative sub-samples were monitored in purpose-built underwater cages, together with controls, at < 24 h intervals for < 5 days within estuaries. In the laboratory experiments, 155 blue swimmer crabs 'Portunus pelagicus' were examined for their stress and mortality after disentanglement and discarding following simulated gill net capture.