254 



CHEMICAL SENSES 



tory corridor in the gully, during outflowing tides, and spreading out over 

 a wide area of shallow water (6-20 ft; 1.8-6.1 m), where sharks might be 

 expected to encounter the stimuli. 



In four tests, the TMAO-glycine mixture attracted two lemon sharks and 

 a large ray (probably Dasyatis americana) to the vicinity of the channel 

 through the reef. One lemon shark swam against the current, entered the 

 gully, approached the stimulus source bottle, and vigorously bit the bottle 

 (Figures 11 and 12). It is possible that the movements of the tethered 

 bottle in the current supplied visual stimuli that summed with the chemi- 

 cal stimuli to elicit the biting responses. The stimulus bottle at the deep 

 water television site had been firmly anchored inside a concrete block, and 

 was immobile. 



The results of the open sea tests are compatible with the conclusions 

 reached from experiments in the hydrodynamic tunnel and in the large 

 observation pens. The role of rheotaxis in the orientation responses was 

 confirmed, and the adequacy of mixtures of tertiary amines and amino 

 acids for releasing feeding behavior under certain conditions was further 

 supported. The data suggest that moving visual stimuli may be important 

 releasers of biting activity in the final stages of orientation behavior, when 

 sharks are surrounded by higher concentrations of effective stimuli in the 

 water. These observations are also compatible with the conclusions of 



ft^wTft" 4 ?^" * 



Figure 11 Lemon shark approaches TMAO-glycine mixture being released from bottle 

 tethered in a channel through fringing reef. See text for details. 



