Consequences of oral lure retention on the physiology and behaviour of adult northern pike (Esox lucius L.)

After a fish snaps an angler’s line, the hook(s) still embedded in its mouth, the question arises: what will the encounter cost the fish? The consequences of retained gear on the physiology and behaviour of fish is not well understood. This study aimed to quantify the impact of prolonged exposure to a retained lure (simulated break off in recreational angling) to the physiology and behaviour of northern pike (Esox lucius) was studied in a laboratory setting. A combination of blood-based physiological metrics and metabolicrate measurements were used to provide a comprehensive overview of the physiological consequences of lure retention in this species using two different treble hook sizes on metal casting spoons in three different hooking locations. Fine-scale video observations of pike following simulated break off were collected to assess pike interaction with a retained lure and to quantify activity patterns. We found that the retention of a lure did not significantly affect metabolic rate, blood physiology or locomotoractivity of pike. However, gill ventilation rate was found to be elevated in pike hooked deeply in the throat suggesting that lures in obstructive locations may somewhat challenge recovery from exercise. Elevated cortisol levels in these fish compared to wild controls suggests that confinement produced prolonged stress in all treatments that may have affected the physiological and behaviour responses that we observed. Our findings provide important observations about the interpretation of stress-oriented laboratory studies using northern pike and the extrapolation of these results to the wild. Despite our negative findings in relation to lure impacts on pike physiology and behaviour, avoiding break offs would still be advisable for fish welfare reasons.