Experimental data on the odontocetes show them to have excellent 

 underwater hearing, particularly at high frequencies (10 to upwards of 100 

 KHz). These animals generally emit click-like sounds with components in this 

 general frequency region for the purpose of echo location which is an important 

 sensory tool for many species such as the bottlenosed dolphin. These animals 

 make wery effective use of echolocation sounds to detect, locate, and identify 

 underwater objects such as fish and other food items. It has often been 

 postulated that other mammals such as baleen whales and pinnipeds also employ 

 echolocation, a. they also emit click-like sounds on occasion. Their use of 

 these sounds for echolocation, however, has not been satisfactorily 

 demonstrated. Many of the marine mammals are observed to emit tonal sounds, 

 and it is generally agreed that an important use is for communication. These 

 sounds vary greatly in frequency, from around 15 Hz for the Blue Whale to 

 4-20KH2 for the bottlenosed dolphin. The sounds also vary widely in duration 

 and wave-form. Some are nearly pure tones, whereas others have a very complex 

 harmonic structure. 



It is clear that the use of sound by the various marine animals is 

 very complex; so much so that it is not within the scope of this report to 

 address the many species, sounds, and uses in any sort of a comprehensive 

 way. The approach used here is to select a single class of animal, one with 

 maximal relevance to the DCS environmental issues. The mysticete (baleen) 

 whales have been selected for several reasons: (a) they comprise several 

 endangered species (bowhead, humpback, etc.), (b) they are very critical and 

 controversial components of the Alaska, North Slope-Beaufort Sea area slated 



G-21 



