Severity of Barotrauma Influences the Physiological Status, Postrelease Behavior, and Fate of Tournament‐Caught Smallmouth Bass

Abstract

Much research on the fish physiological consequences of tournaments has been conducted to date and has provided anglers and tournament organizers with strategies for reducing stress and mortality. However, one aspect of tournaments that has received little attention is barotrauma. At a fall competitive angling event on Rainy Lake in northwestern Ontario, we evaluated the incidence of barotrauma among tournament‐caught smallmouth bass Micropterus dolomieu; we then tagged and released a subset of fish that had severe barotrauma indicators and compared physiology, postrelease behavior, and fate between these fish and those with negligible signs of barotrauma. Overall, 76% of fish had at least one sign of barotrauma (either hemorrhaging or swim bladder distention), but only 32% of fish had two or more indicators and were thus deemed to have severe barotrauma. When telemetered fish were released at a common site, we determined that fish with negligible signs of barotrauma evacuated the release site more rapidly than fish with severe barotrauma did. Some fish with barotrauma floundered at the surface when released, and one of these fish was subsequently hit and killed by a boat. At the end of the monitoring period, 20% of fish with severe barotrauma had died; two additional individuals (20%) that were still at the release site were moribund (failed to respond to diver stimuli). Conversely, we failed to observe any mortality in fish with negligible signs of barotrauma. All tournament fish had elevated levels of blood glucose and lactate. However, stress indices were higher in fish with barotrauma and tended to be highest among fish with barotrauma that died after release. This study revealed that the incidence of barotrauma in tournaments can be high; moreover, outside of a laboratory environment, a significant proportion of fish with severe barotrauma may die after release. Additional research is needed to determine the seasonal variation in incidence and consequences of barotrauma as well as the effectiveness of different depressurization techniques in the field that could be used during fishing tournaments.

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.…”

“…Tournament-captured fish are likely to have high levels of plasma lactate due to intense exertion [29,33,34]. In these studies, aspartate aminotransferase (AST) and other blood chemistry indicators of stress were highest among fish with severe barotrauma.…”

“…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. As the epilimnion continues to warm over the course of the summer season, black bass, especially smallmouth bass, may retreat to deeper water near the thermocline [32].…”

“…Only 30% of fish in that study exhibited barotrauma. Studies of the relationship between barotrauma and mortality in catch and release, freshwater settings have found that between 10-20% of fish exhibiting signs of barotrauma (external indicators as well as blood chemistry changes) die as a result [29,35]. Given the relatively low percentage of fish arriving at Plattsburgh tournaments exhibiting barotrauma, it is likely a minimal contributor to tournament-related mortality.…”