Biologgers reveal unanticipated issues with descending angled walleye with barotrauma symptoms

Abstract

Without sufficient time to diffuse air from their swim bladders, physoclistous fish caught in deep water can exhibit symptoms of barotrauma. In this study, we tested the effectiveness of four barotrauma relief techniques on 76 walleye ( Sander vitreus) and compared their 10 min post-release behaviour and depth selection with an untreated control group using a biologger containing a tri-axial accelerometer and depth sensor. Vented fish showed the best success rate of returning to depth, while no untreated controls were able to swim down. For fish that remained at depth, half were found to have lost orientation and were upside down during the entire monitoring period, with this orientation being strongly associated with the relief method. Vented fish had higher chances (80%) of remaining in the correct orientation at depth compared with the other methods (average of 38%). Our research shows that the best way to prevent negative outcomes of barotrauma is to avoid fishing at depths that yield barotrauma; however, if unavoidable, affected fish should be carefully vented by trained anglers to best reduce post-release impairments.