Blue whale (Balaenoptera musculus) vocalizations recorded in the North Pacific Ocean: Geographic, seasonal and diel variation

The objective of this research was to improve our understanding of blue whale distribution and seasonality by use of acoustic detection of blue whale vocalizations. Blue whale vocalizations are long (>15 s), low-frequency (∼20 Hz) sounds that are often repeated in stereotypic patterns. Recordings from hydrophones located in the North Pacific were examined for the presence of known blue whale sounds in order to assess geographic, seasonal and diel variation within these patterns. This effort began with an acoustic survey of the eastern tropical Pacific (ETP) to document the acoustic presence of low-frequency whale sounds. Two call types that have been attributed to blue whales were detected often and these different types appear to represent northern and southern hemisphere populations. Another broad survey was undertaken but rather than enumerate the showed similar seasonal patterns in the North Pacific but east-west geographic differences. The last survey in this study compared data on a north-south basis to study the acoustic range of the northeastern Pacific call type. This call type is recorded in the northeast Pacific from Vancouver Island, Canada to the equator. It is possible that this call type represents a unique population of blue whales that migrate along the west coast of North America. A closer examination of vocalizing behavior in blue whales was undertaken to study whether or not there is diel variation in blue whale calls in the ETP. More blue whale calls were detected during twilight and dark hours than during light hours.