Abstract:

Masked hearing thresholds of a beluga vocalization in four types of noise were measured during behavioral experiments with one beluga whale. In particular, propeller cavitation noise and bubbler system noise created by an icebreaker were studied and compared to naturally occurring icecracking noise and artificially created Gaussian white noise. Critical signal-to-noise ratios, at which each noise just masked the beluga vocalization, were used for ocean sound propagation analysis. A three-point scenario was established involving the relative distances between a noise-creating icebreaker, a vocalizing beluga whale, and a listening conspecific. Maskograms are color plots visualizing the two overlapping sound fields and indicating zones of masking around the noise source. Results are that propeller cavitation noise (source level 200 dB re:1 (mu)Pa at 1 m) has a maximum radius of masking of 23 km. Bubbler system noise (source level 190 dB re:1 (mu)Pa at 1 m) masks over 15 km. The masking zone around natural icecracking noise (source level 150 dB re:1 (mu)Pa at 1 m) has a radius of only 10 m. This is the same for broadband Gaussian white noise with a source level of 160 dB re:1 (mu)Pa at 1 m.