Fig. 3. (A) Number of approaches by snappers to <50 cm from the experimental shelter during the ammonia and urea treatments, separated into 10-min intervals. There were no significant differences among time intervals for either odorant with repeated measures ANOVA. (B) Ammonia concentration (mean ± s.e.m., N=10) from the calibration of the odorant delivery system. 33 mmol N l^-1 NH₄Cl was delivered for 30 min (1.67 ml min^-1) followed by ambient seawater. The shelter's internal ammonia concentration (after mixing) was sampled via the access port.