Effects of air exposure on survival of Yellowstone Cutthroat Trout angled from a stream with warm water temperatures

We evaluated the effects of air exposure on Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri caught and released in a cold-water stream with elevated water temperatures (i.e., > 14°C) in southeastern Idaho. Anglers caught fish in a 2.3-km section of Fall Creek, Idaho, during August 2018. Sampled fish remained underwater while we measured and then tagged them with T-bar anchor tags. We exposed fish to air for 0, 30, or 60 s and then released them at the point of capture. We continuously monitored temperature during the study period. Water temperatures during the study varied from 10.0 to 19.7°C and averaged 14.9°C (SE = 0.08). In total, anglers caught 161 Yellowstone Cutthroat Trout over 10 d. Of those fish, we did not expose 54 to air; we exposed 54 to air for 30 s, and 53 for 60 s. We used electrofishing to recapture tagged fish and estimate relative survival. Relative survival was highest for fish exposed to air for 60 s (0.40 [SE = 0.25]) followed by 0 s (0.35 [SE = 0.25]) and 30 s (0.30 [SE = 0.27]), but differences were not statistically significant. Results from this study are consistent with other air-exposure studies suggesting that air exposure of 60 s or less is not likely a concern in Yellowstone Cutthroat Trout fisheries. Releasing fish as quickly as possible is always encouraged, but management regulations restricting air exposure seem unnecessary given the collective body of field-based research on air exposure. Nevertheless, similar studies on other systems and species are warranted.