Interactive effects of fish handling and water temperature on reflex impairment of angled Rainbow Trout

Catch-and-release angling is a popular recreational activity that has been shown to have impacts on fish welfare. Angler behaviour (e.g., choice of gear type, handling time) and environmental conditions (e.g., water temperature) during angling events have been documented to influence fish condition and post-release survival. This is particularly true for air exposure duration and water temperature, which are known as two of the most significant determinants of the fate of released fish. Here, Rainbow Trout (RBT; Oncorhynchus mykiss) were angled and air exposed for a random duration of time ranging between 0 and 120 seconds across a range of water temperatures (12–26°C). Reflex impairment was assessed on a binary scale using vestibular-ocular response, burst swimming response, and ability to return to equilibrium as indicators. Dehooking time and fight duration of angling events were also recorded. Our results revealed a positive relationship between total reflex impairment and water temperature, air exposure, dehooking time, and body size (total length). At the warmest water temperatures, reflex impairment was consistently high even for fish exposed to air for mere seconds regardless of other angling behaviours. At cooler water temperatures and air exposure times greater than ∼70 seconds, reflex impairment levels were moderately high. When water temperatures were relatively cool and air exposure times were shorter (>70 seconds) reflex impairment was moderate. Based on these results, we suggest anglers targeting RBT during warm-water periods minimize overall handling time and air exposure, or avoid targeting RBT altogether. These best practices should help improve fish welfare and post-release survival.