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

Abstract

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.

Use of external Indicators to Evaluate Stress of Largemouth (Micropterus salmoides) and Smallmouth (M. dolomieu) Bass at Tournaments

“…The percentage of fish exhibiting barotrauma in Lake Champlain tournaments was comparable to percentages observed in other studies, which indicate that instances of severe barotrauma can range from 1.9% on shallow lakes to 56.5% on deeper lakes [28,29,33]. Although Fig.…”

“…In many studies, hemorrhaging in fish fins is categorized as an indicator of barotrauma [28,29,33]. In our study, bloody fins were not significantly correlated with any other indicators of barotrauma.…”

“…Lake Champlain has an average depth of 19.5 m, that number is skewed by the deep trenches in the Main Lake, an area rarely frequented by bass anglers (<1% of fishes in this study came from that area of the lake). Discounting the Main Lake, Lake Champlain's average depth is approximately 6 m. On the St. Lawrence River, incidence of barotrauma began to increase gradually at 6 m and did not increase dramatically until depths over 10 m [28]. Only 30% of fish in that study exhibited barotrauma.…”

“…Further literature surveys revealed differences in methodology that lend further credence to this hypothesis. A comparison of three studies on waters in northeastern North America (Morrissey et al [33] on Lake Erie, Gravel and Cooke [29] on Rainy Lake in Ontario, and Schreer et al [28] on the St. Lawrence River) found similar levels of bloating (27% -41%). Morrissey et al [33] and Gravel and Cooke [29] also had similar levels of hemorrhaging (62% -66%), but Schreer et al [28] had much lower levels of hemorrhaging (< 4%).…”

“…Incidences of barotrauma increase dramatically if fish are angled from depths > 5-6m [28,29]. Both conventional fisheries management texts [30,31] and research into barotrauma [29] indicate that black bass move into epilimnetic waters in the summer months.…”