Abstract
Bonefish Albula vulpes ( n = 7) exercised to exhaustion and air exposed for 1 min as part of a catch‐and‐release angling event were found to excrete both ammonia and urea, but cortisol and lactate were below detectable levels. Urea made up a greater proportion of total nitrogen excretion from these fish at all time points following an angling event. When captive juvenile lemon sharks Negaprion brevirostris ( n = 12) were exposed to a 30 s pulse of these chemicals [ammonia (500 mM), cortisol (20 µg l −1 ), lactate (6 mM) or urea (3 mM)], they showed a significant reduction in the frequency of resting behaviours when exposed to ammonia and urea than when exposed to control water. It appears that products excreted by A. vulpes , particularly ammonia and urea, may provide an olfactory cue for the post‐release predation of A. vulpes by N. brevirostris during catch‐and‐release angling events.