1. The animal may associate the sound with previous experience. 

 Such recognition, for man, normally requires a sound level many dB above that 

 of bare detection. 



2. The sound may become so loud that the magnitude of the hearing 

 sensation alone elicits aversive behavior. VJith man, for example, most sounds 

 do not become uncomfortably loud until they are about 100 or more dB above the 

 auditory threshold. 



F. This report does not address the interfering, or masking effects, 

 that the platform noise may have on sounds such as communication signals 

 emitted by marine animals. Data for some such predictions are now available. 

 This is an important area for future analysis. 



Estimates of such interference require a knowledge of the frequency 

 spectrum, source level, and directional properties of the communication sounds 

 of the species of animal under consideration. Data on spectrum and source 

 level of sounds thought to be communication signals emitted by several species 

 of cetacea are available. Directional data are meager. However, calculations 

 assuming omni-directional ity could be useful as an initial exploratory step. 



C-35 



