Effects of Air Exposure on Survival of Yellowstone Cutthroat Trout Angled from a Stream with Warm Water Temperatures

Abstract

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.

Low‐level infection of parasitic copepods on Rainbow Trout does not affect vulnerability to angling or short‐term survival following catch‐and‐release angling

“…2018, 2019; McCarrick et al. 2019). The fish were kept in the water as much as possible while processing before the air‐exposure treatment.…”

“…Following McCarrick et al. (2019), we estimated the relative survival of infected and uninfected Rainbow Trout after catch‐and‐release angling in October as the proportion of recaptured fish that was in each treatment group. The proportions and 95% confidence intervals (CI) were calculated using standard formulas (Zar 1999).…”

“…We then compared the relative survival rates between the infected and uninfected Rainbow Trout by comparing the differences between the proportions of recaptured fish, with 95% CIs (Scheaffer et al 2006). We considered the short-term survival of infected and uninfected fish after being caught and released to be significantly different if the 95% CI around the difference in proportions did not contain zero (Schill et al 2016;Roth et al 2018;McCarrick et al 2019).…”

“…We sampled a shorter study reach in October to increase the probability of recapturing fish in the air-exposure study (see below). We used the same gear and processing methods as we did for our angling survey in May 2020 but included a stress test (air-exposure treatment) to determine the effects of parasitic copepods on the shortterm survival of Rainbow Trout (Roth et al 2018(Roth et al , 2019McCarrick et al 2019). The fish were kept in the water as much as possible while processing before the air-exposure treatment.…”