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CHEMICAL SENSES 



water photographic enclosures at either end of the test pen. For testing at 

 night, the most active feeding time of nurse and lemon sharks, a 1300-lumen 

 electron flash unit, in a floating housing, was attached to the dorsal fin of 

 the experimental shark. By using an open-shutter photographic technique, 

 allowing the 1/s flashes from the towed electronic flash units to mark the 

 shark's position at 1-s intervals, it was possible to make "track records" of 

 the orientation and swimming paths of sharks (Figures 7, 8, and 9). Further 

 details of this method have been reported by Mathewson and Hodgson 

 (1972). 



Table 1 summarizes results of the wide variety of chemicals and extracts 

 tested with lemon and nurse sharks in the hydrodynamic tunnel and the 

 large observation pens. No significant differences were found in the kinds 

 of chemicals stimulating the two test species. Significant changes in EEG 

 patterns from forebrain or olfactory bulb are indicated by a "+*' in Table 1, 

 with unusually strong EEG effects indicated by "++." Orientation to the 

 chemical stimulus, followed by at least brief searching or approach behavior, 

 is indicated by a "+" in the behavioral response column. Persistence of 

 orientation behavior beyond 10 s, or a display of "feeding frenzy" behavior 



Figure 7 Blinker trail, showing path of nurse shark homing on a stimulus source (TMAO 

 and betaine) by true gradient searching, or klinotaxis. The stimulus source is located at 

 the far end of the observation pen, at the bright spot caused by the shark staying in that 

 vicinity, once the stimulus is reached. 



