Annual, seasonal, and diel patterns in blue whale call occurrence off eastern Canada

Abstract

Little is known about the year-round occurrence of blue whales in Atlantic Canadian waters. We used passive acoustic monitoring to investigate blue whale call presence and increase our understanding of year-round blue whale occurrence along the eastern edge of the Scotian Shelf, Nova Scotia, Canada. Blue whale calls were recorded at 3 deep water sites within and near the Gully Marine Protected Area from October 2012 to September 2014 using bottom-mounted passive acoustic recorders. Calls were categorized as either tonal or downsweeping. At all 3 sites, tonal calls occurred most often from November through January in both years and in August 2014, while the majority of downsweeping calls occurred during May through September 2014. There was no discernible diel pattern in the occurrence of tonal calls. Downsweeping calls occurred most often during evening twilight, with a dramatic peak in occurrence during the hour of 19:00 Atlantic Standard Time at all 3 sites. The peak in downsweeping call occurrence during evening twilight may have been related to blue whale foraging ecology. This study sheds light on the poorly understood year-round occurrence of blue whales off Atlantic Canada. Understanding when and where blue whales occur will help to inform management decisions for the protection and conservation of this endangered population.