Annual decrease in pulse rate and peak frequency of Southeast Pacific blue whale song types since 1970

We examined the decrease in the frequency of the dominant southeast Pacific blue whale song type (SEP2) from 1996 to 2017, using acoustic data from five different sources ranging between the equator and Chilean Patagonia. The pulse rate of the song units as well as their peak frequency were measured using two different methods (summed auto-correlation and Fourier transform). We assess the sources of error associated with each measurement. There...