Simulated catch-and-release using experimental hyperbaric chamber trials reveal high levels of delayed mortality due to barotrauma in mulloway (Argyrosomus japonicus)

摘要

A key factor affecting survival of fish captured from depth and subsequently released is barotrauma - a suite of injuries caused by expanding swim bladder gas and formation of gas embolisms resulting from the decreasing ambient pressure experienced during capture. Mulloway (Argyrosomus japonicus) are an economically-important fishery species in southern Australia often released from deep-water capture suffering from barotrauma. Hyperbaric chambers were therefore used to simulate various catch and release (C&R) scenarios on A. japonicus which allowed the influences of capture depth, surface duration and repressurization on survival and behaviour to be examined in a controlled environment combined with long-term monitoring post-simulation. In Experiment 1, simulated C&R from an acclimation pressure equivalent to 10, 30 or 50 m depth (n = 24 per depth) with a 2 min surface interval resulted in 8% mortality from 10 m increasing to 46 and 50% mortality from 30 and 50 m respectively; mortality delayed by an average of 64 d (range 5-219 d). A second C&R simulation depressurized A. japonicus individuals from either 10 or 30 m - followed by either repressurization after 10 min (Group R), or no repressurization (Group S) (n = 8 for each group). There was 0% mortality from 10 m for both groups, but from 30 m mortality was 100% for Group S and 88% for Group R. All Group S mortality and 38% of Group R mortality was immediate ( 10 min), the remaining 50% of Group R mortality delayed by an average of 21 d. Barotrauma symptoms also increased in severity with increasing depth and surface interval. Immediate mortality was consistent with the formation of gas embolisms in tissues, whereas delayed mortality was likely caused by declining physical condition resulting from loss of buoyancy control caused by gas escape via swim bladder perforation and body wall rupture. Results from these experiments show the potential for delayed mortality in barotrauma-affected A. japonicus to be considerable even when successfully repressurized, casting substantial doubt over the suitability of A. japonicus as a deep-water C&R target species.