Beluga whale echolocation signals in two different ambient noise environments

The echolocation signals of a Beluga whale (Delphinapterus lecus) were measured, first in San Siego Bay, and later in Kaneohe Bay, Oahu, Hawaii, while the animal was performing a target detection task. The ambient noise of both bays is dominated by snapping shrimp, with the noise level in Kaneohe Bay typically 20 dB greater than in San Diego Bay. In San Diego Bay, the animal emitted clicks with peak frequencies between 40 and 60 kHz, and bandwidths between 15 and 25 kHz. When the animal was moved to Kaneohe Bay, it used higher frequency clicks with peak frequencies between 100 and 120 kHz, and bandwidths between 20 and 40 kHz. The shift in the peak frequencies was probably caused by the difference in the ambient noise environment between the two sites, and may represent an attempt by the animal to optimize the signal‐to‐noise ratio during the target detection task. The whale also emitted signals with higher source levels and source energy flux densities in Kaneohe Bay than in San Diego Bay, even though the detection task in Kaneohe Bay was relatively simple and the task in San Diego Bay was relatively difficult.