Marilyn E. Dahlheim
Natl. Marine Mammal Lab., NMFS/AFSC, 7600 Sand Point Way N.E., Seattle, WA 98115
Responses of gray whales to increased levels of noise were documented during playback experiments. Nine sound parameters were compared between control and experimental conditions: call rates, call types, frequency range (Hz), emphasized frequencies (Hz), received levels of sound (dB re: 1 (mu)Pa), call duration (s), calls exhibiting frequency modulation, pulses per series, and signal repetition rates. Whale surface behavior (i.e., dive durations, movements, and abundance) was also investigated. Analyses yielded: a description of call types; a characterization of acoustical habitats; and a determination of relationships between whale calls and habitats; and a determination of relationships between whale calls and habitats. Gray whales employed multiple behavioral strategies (e.g., modification of calling to optimize signal transmission and reception, movement out of the study area, etc.) to circumvent increased levels of noise in their environment. Responses varied with sound source and may also differ with geographical range and/or general behavior.