Recordings of vocalizations in the presence of minke whales Balaenoptera acutorostrata were made from a bottom-mounted hydrophone in the St. Lawrence Estuary, a feeding area for some members of the Northwest Atlantic population. Minke whale activity was observed from a hillside hut and notes were taken with regard to position and swimming direction throughout each recording. The vocalizations were correlated consistently with the occurrence of minkes and sequential sound levels were commensurate with the whale's relative proximity to the hydrophone. Minke calls were heard in 51% of the recordings examined in detail; calling rates were low (0.1 sounds/min-3.6 sounds/min with multiple individuals). The predominant call was a 0.4 sec downsweep in frequency, beginning at 100-200 Hz (median = 118 Hz) and ending below 90 Hz (median = 80 Hz). The change in frequency was variable, between 20 and 70 Hz (median = 42 Hz). Frequency and temporal characteristics of the vocalizations were similar to those recorded from Antarctic minkes by Schevill and Watkins (1972). Comparisons of the minke downsweep with those from the closely related finback whale B. physalus, which is also common in the area, indicated that minke whale calls had higher initial frequencies, greater changes in frequency, and shorter call durations.
Acoustic censusing, bioacoustics, baleen whale