Behaviour of pike (Esox lucius L.) in response to angler-induced disturbance in a catch-and-release fishery in Lake Kleiner Döllnsee

In the northern hemisphere, pike (Esox lucius L.) is one of the most important recreational fishery resources, and regulatory or voluntary catch-and-release angling is common. Only little information is available about the potential sublethal impacts of catch-and-release on pike. The present study addressed this issue by quantifying the behavioural and physiological responses of pike to angler-induced direct (catch-and releaseevent) and indirect (e.g., boating, angling-activity related disturbance of habitat) disturbances, thereby testing basic ecological predator-prey theory and providing insights for management. The main hypothesis of the present work was that pike reduce activity in response to angler-induced disturbances that should be perceived by individual pike as being similar to natural predation risks. During a seven month tracking period, long-term behavioural alterations in a catch-and-release fishery and short-term behavioural changes post release were monitored in a small (25ha) lake in north-eastern Germany, where N = 20 radio-tagged pike were monitored for behaviour and habitat choice once a week for 24 h. Additionally, the link between short-term behavioural changes to the degree of physiological disruption was tested in a large (787 ha) lake in eastern Ontario, Canada, where angled pike (N = 52) were stressed in four air exposure treatments (and one left-lure treatment with 0 s air exposure) and blood sampled thereafter. After release, the behaviour was monitored for short-term (1 h) and mid-term (3 days) periods and the link between physiological indicators (e.g., blood lactate levels) and behavioural change was assessed. Angler-induced predation risk through disturbance stimuli such as boating and continuous catch-and-release angling caused long-term behavioural alterations of pike. Pike altered their habitat choice with increasing predation risk (increasing angling intensity), preferring reed as refuge. In response to catch-and-release angling, pike also reduced their distance to the shore and the size of their individual residence area. Movement rates per day as indicator of pike activity decreased with increasing fishing intensity supporting the main hypothesis of the present work. In the short term directly after capture, minimum displacement per hour and distance to shore were significantly lower compared to the situation prior to the capture event, but these impacts disappeared within a week post capture suggesting that pike resumed their normal behavioural patterns. Blood lactate levels as indicative of exhaustion and anaerobic metabolism rose significantly in all air exposure treatments compared to control fish, and the intensity of physiological disturbances after capture caused by playing, different degrees of air-exposure, and a left lure influenced the degree of behavioural alterations post release. Pike exposed to air for 300 s after capture showed significantly higher inactivity in the first hour post released compared to all other treatments. However, behavioural alterations after exhaustion through catch-air exposure-and release vanished after one day suggesting quick recovery. In conclusion, anglers in a catch-and-release context can indeed act as a predation threat and thereby sublethally affect behaviour and habitat choice of pike. This adds a new dimension tothe well-known lethal impacts associated with pike angling, which, from aconservation perspective, calls for minimization of potentially stressful activities such as boating or air exposure. There remains the potential that sublethal alterations might impact on the individual fitness by, for example, influencing somatic growth or reproductive output post release. The present study could not answer this important question, which is left for further research.