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PACIFIC SCIENCE, Vol. XVII, April 1963 
Fig. 12. Activity index during successive 2-min periods, illustrating response of starved blacktip sharks 
to "quiescent grouper water,” to "distressed grouper water,” and to "dead grouper water.” 
The sharks again responded with a violent hunt- 
ing response and tube biting. The procedure was 
repeated after an additional 4 hrs (at 2200) 
during which time the quiescent grouper water 
had been flowing into the compartment and the 
sharks were responding normally. The small 
grouper in the dip net, however, had died. After 
the dead fish was lowered into the container 
(at 2210), there was a spectacular hunting re- 
action by the sharks. Only the string was re- 
covered from the container at the end of the 
third period: the small dead grouper had been 
swallowed by one of the larger "quiescent” 
groupers. The water in the container was clear 
indicating that the fish had been engulfed whole 
without the escape of body juices. 
The above experiment was repeated on the 
starved blacktip sharks, using the same four 
"quiescent” groupers and another "distressed” 
grouper. In this case the "distressed” grouper 
was not eaten after it had died. The results (Fig. 
12) were almost identical to those obtained with 
the starved grey sharks. A similar test using 
four "quiescent” and one "distressed” mullet 
gave similar results (Fig. 13). The sharks even 
responded to a small "distressed” blacktip shark 
which was held in a dip net for a few minutes 
and then, still alive, was lowered into the con- 
tainer, in this case in the absence of any "quies- 
cent” fish. 
Discussion 
These experiments show that "quiescent” prey 
give off an odor which can be detected by sharks 
when it is first introduced into their environ- 
ment but to which they soon become habituated. 
There is still the question, of course, as to 
whether the "quiescent” fish were still under 
stress because of the artificial environment of 
the plastic container. Regardless of this, the 
experiments demonstrate that when the prey 
becomes frightened and excited it gives off an 
additional or a new odor which again stimulates 
the habituated sharks, provoking the typical 
