Marine Mammal Auditory Systems: a Summary of Audiometric and Anatomical Data and Its Implications for Underwater Acoustic Impacts

Audiogram: A graph of hearing ability charting frequency (abcissa) vs. sensitivity measured as sound pressure or intensity (ordinate). Cetaceans: Whales and dolphins decibel (dB): a scale based on the log ratio of two quantities. It is commonly used to represent sound pressure level or sound intensity. The value of the decibel depends upon the denominator used, or reference pressure. Therefore the decibel level of sound is properly stated in the form of n dB re n microPa . The microPascal is a unit of pressure; e.g., 100 dB re 20 microPa in air equals 160 dB re 1 microPa in water. infrasonic: below 20 Hz, the lower limit of human hearing kHz: kilo Hertz. A Hertz (Hz) is a measure of sound frequency equal to 1 cycle/sec, therefore a kHz is one thousand cycles per second. Mysticetes: Baleen or moustached whales, which include rorquals. The largest whales, all of which are opportunistic gulp or seine feeders. They are not known to echolocate. Octave: An octave is broadly defined as a doubling of frequency. Thus, a one octave shift from 500 Hz is 1,000 Hz, and from 3,000 Hz, it is 6,000 Hz. Adult humans have on average an 8-9, octave functional hearing range from 32 to 16 kHz.. Odontocetes: toothed whales. All are believed to echolocate; i.e., to use a biosonar for imaging the environment via sound and sound analyses. Pinnipeds: Seals, sea lions, walruses. ultrasonic: above 20 kHz, the upper limit of human hearing.