Northeastern Pacific Blue Whale Offshore Call Variability

Abstract

Blue whales are a species that are found worldwide that are split into several subpopulations. The northeastern Pacific subpopulation produces A- and B-type calls that can formed into AB- and ABB-type phrasing. In the Southern California Bight, it was found that ABB-type phrasing was more prevalent than AB-type in deeper offshore sites than near-shore sites. The subpopulation migrates north near fall close to the Washington and Oregon coast where their calls are recorded by hydrophones. Spectrogram data of sounds from this region were analyzed first for B-type calls using automatic detection. Later manual analysis was conducted to detect A-type and B-type calls in randomly selected times. Between 2018 and 2019 at this site, ABB-type made over half of the phrases sampled. B-type calls in general were also had a near 2:1 ratio compared to A-type calls for all reported months. This would suggest that the pattern found for offshore blue whale calls holds true. Overall B-type calls appear to be the favored call for offshore environments due to their ability to be transmitted over longer distances, potentially improving their ability to mate.