surface, the bottom, and the sub-bottom at several levels before it reaches 

 the measurement station (Drouin, 1974). Many of the data presented in this 

 report show a large amount of variability, probably due to shallow-water 

 propagation characteristics. 



Information on the effects of sustained, sub-critical levels of noise on 

 the behavior and responses of marine animals is poorly understood. Although 

 underwater hearing threshold data is available for some species, this 

 information is not sufficient by itself to predict the effects of noise on 

 behavior. 



This report is divided into two sections. Section I summarizes 

 published acoustic data from drilling platforms, construction sites, and 

 support craft associated with offshore drilling activities. These data are 

 presented as source levels and specify the amount of sound radiated by a 

 projector. Source level is defined as the ratio of the intensity of radiated 

 sound in decibels to the intensity of a plane wave of rms pressure 1 u Pa 

 referred to a point 1 m from the acoustic center of the projector in the 

 direction of the target. 



Section II, discusses the underwater hearing and underwater hearing 

 thresholds for cetaceans and pinnipeds, and discusses sound production by 

 large whales. 



A-3 



