Relationships of scale cortisol content suggest stress resilience in freshwater fish vulnerable to catch-and-release angling in recreational fisheries

Abstract

The capture by angling of an individual fish is recognised as a short-term physiological stressor. In fish populations exploited by catch and release angling (C&R), there is potential for some individual fishes to be captured on multiple occasions, but the longer term physiological consequences of this remain uncertain. Using scale cortisol content as a biomarker of chronic stress and scale samples from two fish populations exploited by C&R angling, we developed proxies of angling capture vulnerability before testing these proxies against scale cortisol content. In a riverine population of European barbel Barbus barbus, fish with the highest scale cortisol content were predicted as those sampled by angling rather than electric fishing, as angled fish had significantly smaller home ranges and diets based primarily on angling baits. In a population of common carp Cyprinus carpio in a small pond fishery, we predicted that fish with the highest scale cortisol content would be those with higher proportions of angling bait in their diet. In both species, however, the fish predicted to be most vulnerable to angling capture had the lowest levels of scale cortisol content. We suggest that this is through fish that are captured regularly being highly stress resilient (with this independent of other traits) or fish with traits that suggest high capture vulnerability being able to minimise their recapture rates through developing hook avoidance behaviours after an initial capture. Overall, these results suggest that scale cortisol content is a useful biomarker for measuring chronic stress from C&R angling.