Characterization of blue whale ( Balaenoptera musculus ) audible calls recorded in the Northwest Atlantic

Blue whales (Balaenoptera musculus) produce infrasonic calls (A, B, and AB), which are very low-frequency (16-20 Hz) vocalizations made by males for reproductive purposes, and higher frequency (25-120 Hz) audible calls (downsweep and arch), which are produced by both sexes potentially for feeding and/or socializing purposes. Infrasonic calls have been well characterized and tend to be observed more in winter, whereas audible calls tend to be observed more in summer. This paper quantifies the duration and frequency characteristics of audible calls from recordings collected in the Northwest Atlantic off eastern Canada. There were at least 5 distinct subtypes among the 132 calls examined: short, medium, and long downsweeps were primarily differentiated by duration and shape, hooks began with a limited bandwidth upsweep followed by a downsweep, and arches began with a near-full bandwidth upsweep followed by a downsweep. The variation in start, end, minimum, maximum, and peak frequencies, as well as bandwidth, duration, and slope of the upsweep and/or downsweep portions of all calls were measured for each audible call subtype. These descriptions can support future blue whale passive acoustic studies, including more rigorous examination of seasonal acoustic occurrence, differences among call types, and comparison between populations.