SHARKS AND UNDERWATER SOUND 



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TEST PERIODS 

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TOTAL SIGHTINGS DURING TEST PERIOD 



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 DURING TEST PERIOD 



o  TOTAL SIGHTINGS DURING CONTROL 

 PERIOD 



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Figure 4 Decrease in sightings of sharpnose sharks, Rhizoprionodon sp., 

 through successive test periods. Signals consisted of constant level, irregularly 

 pulsed, overdriven 80 Hz sine waves (biphasic, symmetrical, and distorted 

 square waves). Each test and control period— 3 min. (Myrberg et al. 1969) 



opposite to that of rapid approach, i.e., withdrawal— elicited by the use of 

 sound. This unique pattern of response was reported by Banner (1972) 

 during his bioacoustical study of young lemon sharks. His close attention to 

 their behavior provided coherent clues as to probable causal relationships. 

 Rapid flight appeared to occur at the precise moment certain sounds began. 

 This was particularly true if sharks were approaching the source. Banner 

 noted, however, that sounds consisting of closely spaced pulses rarely caused 

 such responses. He thus hypothesized that during rapid approach, short 

 intervals allowed the signal level to increase smoothly, which would not 

 occur when a loud, impulsive sound, such as a single pulse or a signal possess- 

 ing long intervals (seconds in length) was projected. Long intervals resulted 

 in sudden jumps in level being experienced during an approach response. 

 Only these two sound types, interestingly, elicited the so-called "startle" 

 response in this study. As in the case of attraction, Banner found that these 

 "startle" responses occurred only when the projected sound level at the loca- 

 tion of "startle" was well above the established threshold sensitivity. 



Strikingly similar withdrawal responses were first observed in silky sharks 

 by our team in 1970 during a field study in the Tongue of the Ocean, 

 Bahamas. Water depth was approximately 2000 m at the test site, and the 



