Temperature effects on the physiological status and reflex impairment in European grayling Thymallus thymallus from catch-and release angling

Abstract

There is a growing body of research communicating how angler behaviour can be adjusted and optimised to reduce fish injury and impairment resulting from the capture of recreationally angled fishes. However, few studies have focused on how individual and interacting abiotic variables influence the outcomes of catch and release (C&R) angling. A population of European grayling Thymallus thymallus at their upper thermal limit of their geographic distribution provided a model cold-water species that was representative of other fishes sensitive to climate warming impacts and that are subjected to C&R across different seasons. Here, C&R angling for T. thymallus was conducted during summer (>15 °C) and winter (<10 °C), with 97 fish captured (220–490 mm). Measurement of tertiary stress responses (reflex impairment, as time to body equilibrium, an important predictor of post-release mortality) revealed that at >15 °C, fish took significantly longer to regain equilibrium (178 ± 44 s) than at <10 °C (70 ± 40 s). Multivariate testing revealed air exposure had a stronger effect on reflex impairment than fight time. Testing of post-capture, pre-release blood chemistry on sub-samples of captured fish revealed fish had significantly elevated levels of both glucose and lactate at >15 °C versus <10 °C, In entirety, these results suggest that stress responses and post-release mortality risk in cold-water fishes subjected to C&R could be reduced via temperature-informed fishery management practises, and by minimising, or ideally eliminating, air exposure