Acoustic data from the spring 2011 bowhead whale census at Point Barrow, Alaska

Abstract

Arrays of bottom-mounted passive acoustic recorders were used to continuously record the sounds of bowhead whales migrating past Point Barrow, Alaska for a period of 105 days in April–July 2011, spanning the duration of the visual census. Recorders were deployed in a roughly linear array configuration near the edge of the shorefast ice bordering the open lead. The recorded acoustic data were analysed from 156 sample periods comprising a total of 331 hours coincident with the visual census. Bowhead sounds in the sample periods were found by manual inspection of multi-channel sound spectrograms of the array recordings. Source locations for bowhead sounds that were received on three or more sensors within the array were calculated using a robust localisation algorithm. Very high levels of bowhead acoustic activity were observed in comparison to recording efforts undertaken during past censuses, including high rates of singing and call sequences. A total of 22,426 bowhead sounds yielded 15,647 reliable locations. Of these, 6,944 were within the rectangular aperture zone directly in front of the array and therefore used in the calculation of a new population estimate. This paper summarises one of three critical component of the research program leading to the 2011 estimate of abundance of Givens et al. (2016) and is therefore a cornerstone of the scientific basis for IWC Scientific Committee advice for this whale stock.