The effect of vessel noise on the vocal behavior of Belugas in the St. Lawrence River estuary, Canada

During June-July 1991, we monitored the vocal behavior of belugas before, d uring, and after exposure to noise from a small motorboat and a ferry to de termine if there were any consistent patterns in their vocal behavior when exposed to these two familiar, but different sources of potential disturban ce. Vocal responses were observed in all trials and were more persistent wh en whales were exposed to the ferry than to the small boat. These included (1) a progressive reduction in calling rate from 3.4-10.5 calls/whale/min t o 0.0 or <1.0 calls/whale/min while vessels were approaching; (2) brief inc reases in the emission of falling tonal calls and the three pulsed-tone cal l types; (3) at distances <1 km, an increase in the repetition of specific calls, and (4) a shift in frequency bands used by vocalizing animals from a mean frequency of 3.6 kHz prior to exposure to noise to frequencies of 5.2 -8.8 kHz when vessels were close to the whales.