Nonauditory effects of noise may produce physiological stress, with symptoms analo- 

 gous to exposure to extreme heat or cold (ref 7, 8). An animal's response to stress includes a 

 variety of measurable physiological changes: eg, increased blood pressure, increased cortio- 

 steriod levels, and changes in adrenal gland weight. Prolonged stress can exhaust an animal's 

 resistance to infection and disease and, in extreme cases, can result in the animal's death. 



Noise produces the same general effects in animals and humans: namely, hearing 

 loss, masking of signals, behavioral changes, and nonauditory physiological effects. Labora- 

 tory studies with animals indicate temporary and permanent noise-induced threshold shifts. 

 However, damage risk criteria for most species of animals have not been developed. Physio- 

 logical effects of noise exposure have been demonstrated in laboratory and farm animals, but 

 the degree to which the results apply to wildUfe is unknown. Animals' physiological and 

 behavioral adaptations to noise stimuli are also yet unknown, and definitive research criteria 

 to assess such adaptation have not been developed. In this report, however, judgments of 

 environmental impact will be based on existing, though incomplete, information (ref 2). 



The acoustic environment in areas of offshore drilling activities may influence the 

 behavior of marine mammals. Increased noise levels may mask acoustic signals or reduce 

 the range at which the mammals detect the signals (ref 9). 



The impact of offshore structures and the associated increase in the level of human 

 activities in outer continental shelf areas could disrupt normal migratory routes or displace 

 marine mammals from traditional feeding and breeding areas. Such disruptions could re- 

 duce the biological fitness of a population. 



This report summarizes (1) acoustic data from offshore drilling activities, and (2) 

 the hearing capabilities of cetaceans and pinnipeds and presents data on the underwater 

 hearing of large whales. The report also discusses the possible impact of offshore drilUng 

 activities on natural populations of marine mammals. 



SUMMARY OF LITERATURE 



Underwater noise measurements from offshore drilling activities are sparse. Published 

 surveys and the author's personal contacts with private industry reveal that available infor- 

 mation is bandwidth limited: ie, the measurements at high frequency were limited or the low 

 frequencies were rolled off due to high ambient noise. Shallow water ambient noise measure- 

 ments also are limited. In the shallow water of most offshore drilling operations (ie, less than 

 250 m) accurate source level noise measurements are difficult because of multipath propaga- 

 tion (ref 10). Variability is inherent in the data because sound propagation characteristics 

 vary greatly in shallow water and ambient background noise is strong and variable in shelf 

 areas. 



' Selye. H, Stress and Disease, Science. 122(3171), p 625-631 , 1955. 



° Selye, H, The General Adaptation Syndrome and the Diseases of Adaptation, J Clin Endocrin & Metab, 

 6(2). p 117-230, 1946. 



Myrberg, AA, Ocean Noise and the Behavior of Marine Animals: Relationships and Implications, In: 

 Effects of Noise on Wildlife, JL Fletcher ana RG Busnel, ed, p 168-208, Academic Press, New York, 

 N"/, 1978. 



^ Drouin, AH, Design and Field Operation of an Underwater Acoustic Telemetry System, Offsiiore Tech- 

 nology Conference, 6th, OTC 1965. p 9. 



H-8 



