Stress, predators, and survival: Exploring permit (Trachinotus falcatus) catch-and-release fishing mortality in the Florida Keys

Abstract The biological consequences of catch-and-release (C&R) angling revolve around interactions between the physiological and behavioural responses of the captured fish and ecological conditions such as the presence of opportunistic predators. Here, we explored the consequences of C&R on adult permit (Trachinotus falcatus), including assessments of depredation rates, their physiological and reflex responses prior to release, post-release behaviour, and post-release predation in diverse habitats in the Florida Keys, USA. We found pre-capture depredation rates were highly variable amongst habitat types, ranging from zero on shallow water flats, to 35.3% and 90.1% on specific reef and shipwreck locations, respectively. Observed predators were all large sharks. Importantly, one of the high predation sites is an important permit spawning location, thus C&R fishing in that locale may be a conservation concern. Physiological stress responses (blood lactate, glucose, pH) and reflex tests indicated that permit were relatively robust to routine angling (fight durations of 1 to 12 min) and handling (air exposure up to 2 min). Short duration post-release tracking using tri-axial acceleration biologgers identified no differences in swimming activity for fish that were kept in water versus those held in the air for 2 min to simulate an admiration period. While this study indicates that permit are relatively robust to C&R angling in terms of stress responses and behavioural impairment, high densities of opportunistic predators at certain fishing locations can result in high rates of pre-capture depredation independent of the state of the animal. Permit angling in locations with high predator densities is a potential conservation issue, especially if specific locations represent important pre-spawning aggregation sites for fish populations that may be more vulnerable to predation and thus depredation. Current C&R best practices (i.e., limiting fight times and air exposure) may not be adequate to ensure permit survival at high predator density sites. Angling-related depredation is often cryptic, yet is a growing conservation concern in many fisheries – we developed and applied a novel framework for identifying cryptic depredation that may be applicable across fisheries.