bredanensis , Tursiops truncatus gi11i , Tursiops truncatus truncatus, 

 Laqenorhynchus obliquidens , Zaiophus californianus , Phoca vitulina , and 

 Halichoerus grypus . Auditory data are summarized for both pinnipeds and 

 cetaceans in Table 3. Studies giving frequency and intensity thresholds are 

 graphed in figure 11. 



Behavioral Tests - Cetacea 



Kellogg and Kohler (1952) made the first systematic observations of 

 cetacean hearing by playing tones to a group of free-swimming captive Tursiops 

 truncatus and Stenella plagiodon . No training techniques were used, and 

 changes in the animals' natural swimming behavior at the onset of a tone were 

 used as criteria for tone perception. Tones between 100 Hz and 200 kHz were 

 used to obtain a rough outline of the test subjects hearing range. No attempt 

 was made to determine dB intensity sensitivity thresholds. Tonal intensities 

 were maintained at a minimum sound pressure level of 4.03 dynes/cm2 at four 

 meters (118 dB re 1 )uPa) (unless otherwise stated, all dB re 1 fj Pascal). 

 Behavioral differences were noted from 100 Hz to 50 kHz. Later tests on other 

 Tursiops truncatus (Kellogg, 1^53) at other locations indicated frequency 

 responses from 100 Hz to 80 kHz. 



Schevill and Lawrence (1953) tested the hearing range of a single free 

 swimming captive Tursiops truncatus . The animal was tested at frequencies 

 from 150 Hz - 153 kHz, the upper limit of the equipment. Intensity levels 

 were maintained between 100 and 110 dB. The animal had been trained by 

 operant conditioning to swim to a trainer for a fish reward if it perceived a 

 tone. Responses were noted throughout the frequency band tested, from 150 Hz 

 - 120 kHz 50% of the time, at 130 kHz 30% of the time, and from 151 - 153 kHz 

 13% of the time. 



Thirteen years later the first true audiogram giving frequency and 

 intensity thresholds for a marine mammal was made by Johnson (1966) on a 

 Tursiops truncatus . The test subject responded from 75 Hz - 150 kHz. The 

 single test subject was trained using standard operant conditioning techniques 

 to respond to the presentation of a signal by pushing the appropriate 



A- 9 



