The Incidence and Consequences of Barotrauma in Fish in the St. Lawrence River

Barotrauma is increasingly being recognized as a serious conservation and management issue in catch-and-release fisheries. Barotrauma results from decompression that can cause physiological alterations and physical injuries. During the summers of 2007 and 2008, we angled for fish in the St. Lawrence River to determine the incidence of barotrauma injuries and the related mortality rates. An angler survey was also conducted in 2008. A total of 212 fish were caught at depths ranging from 1 to 21 m. Sixty-three fish (30%) showed signs of barotrauma, 99% of these being smallmouth bass Micropterus dolomieu, walleyes Sander vitreus, and yellow perch Perca flavescens. These three species represented 77% of all the fish caught and, excluding round goby Neogobius melanostomus, represented 94% of the fish caught at depths greater than 6 m. Signs of barotrauma were bloating (89%), loss of equilibrium (66%), stomach eversion (62%), bulging eyes (18%), hemorrhaging in the eyes and fins (12%), and anal eversion (5%). Most fish had multiple signs, approximately 50% showing loss of equilibrium, bloating, and stomach eversion. The incidence of barotrauma increased with depth, first appearing at 6.1 m. There was a threshold at approximately 10 m, from which the incidence rapidly increased to 100% at 21 m. Mortality occurred in 67% of the fish with barotrauma, even in those with less severe signs (e.g., mild bloating and slight loss of equilibrium only when stationary) and showed a similar rate of increase starting at 9 m. There were interspecific differences in the susceptibility to barotrauma that may be related to habitat preferences and physiological and physical differences that should be considered when targeting different species and depths.