Environmental constraints on sound transmission by humpback whales

Singing humpback whales in Hawaii produce a variety of sounds at high sourc e levels (ca. 185 dB re: 1 mu Pa), in coastal waters 15-500 m deep. These s ounds are attenuated and distorted as they propagate away from a singer, li miting the utilizable range of the sounds. In the current study, simulation s based on normal-mode theory were used to investigate how the effects of s hallow-water propagation constrain humpback whales' use of sound. It is sho wn that humpbacks can greatly affect transmission range by adjusting their positions and sounds in response to environmental factors. Source depth, in particular, is shown to be a major determinant of which frequencies propag ate the farthest, A preliminary analysis of range-dependent distortion sugg ests that spectral cues can potentially provide listening whales with infor mation about how far a sound has traveled. (C) 1999 Acoustical Society of A merica. [S0001-4966(99)01211-4].