ASA 126th Meeting Denver 1993 October 4-8

4aAB7. The effects of noise on dolphin echolocation.

Whitlow W. L. Au Paul E. Nachtigall

Hawaii Inst. of Marine Biol. and Naval Command, Control and Ocean Surveillance Ctr., RDT&E Div., P.O. Box 1106, Kailua, HI 96734

The echolocation capabilities of dolphins can be seriously affected by natural ambient and man-made noise. Many echolocation experiments have been conducted at our facility to study the effects of noise on the echolocation behavior and capabilities of dolphins. When a beluga was transported from San Diego Bay, California to Kaneohe Bay, Hawaii, the whale adjusted its sonar emissions to compensate for the louder ambient noise environment in Kaneohe Bay. It emitted higher intensity signals which had peak frequencies that were approximately one octave higher than in San Diego. Experiments with echo-locating dolphins have shown that their target detection and discrimination capabilities can be severely degraded by the introduction of masking noise. In most situations, the dolphins compensated for the presence of masking noise by emitting more clicks per scan and by increasing their signal intensity. The response latency defined as the time between the cessation of the last click in a click train and the touching of a response paddle also increased as the masking noise level increased. However, the effects of noise emanating from a specific location can be minimized by a dolphin utilizing the directional property of its auditory system.