Vocalization Behavior and Spatial Distribution of Humpback Whales in the Gulf of Maine from Passive Towed Array Measurements

Abstract

The temporal calling behavior and spatial distributions of humpback whales (Megaptera novae- angliae) during their feeding season in the Gulf of Maine are determined using their vocalizations passively recorded on a towed horizontal receiving array over a three week period in Fall 2006. Over 3000 distinct vocalization signals, each lasting from 1 to 3 s in the 300 to 700 Hz frequency range, could be attributed to humpbacks whales, with over 85% of the calls occurring during nighttime hours. Humpback individuals were found to vocalize at night at an average rate of roughly 1 call per minute with instantaneous call rates as high as 10 per minute over roughly 2 minute durations. The whale individuals were localized in azimuth by beamforming their received vocalizations and in range by application of the synthetic aperture and array invariant tracking methods with accuracies of roughly 10% of the mean range. The vast majority of vocalizing humpbacks were distributed in two distinct regions, the northeastern flank of Georges Bank, in water depths of 50 to 200 m, and the Great South Channel. in water depths of 50 to 150 m. These locations were roughly 70 km and 100 km away from the array respectively. The humpback whale vocalization behavior were found to be independent of active source transmissions in the region since their diurnal calling pattern and vocalization rates are identical for periods with and without source transmissions.