Fig 1.
Map of recording locations offshore of Southern California.
Recording locations H, E, and N are shown as black circles. Color bar indicates depth in kilometers and thin grey lines mark 500 m bathymetry contours. Map generated using the marmap and ggplot2 packages in R [21–23] and bathymetry data from the ETOPO1 database hosted by NOAA [24, 25].
Fig 2.
Northeast Pacific blue whale A and B call.
Calls were recorded on October 17, 2015 at site N. The dashed box indicates the overtone (A call) and harmonic and time point (B call) for which frequencies were used to compare between years.
Fig 3.
Mean frequencies of Northeast Pacific blue whale B calls.
The first 20 s of the 3rd harmonic are shown each year from 2006 to 2019. Shaded areas represent 95% confidence intervals and the dashed line indicates 10 s point that was used for yearly comparisons.
Fig 4.
Mean frequency (a) and pulse rate (b) of Northeast Pacific blue whale A calls from 2006 to 2019. Error bars represent 95% confidence intervals and the dashed black line represents a quadratic fit to the data.
Fig 5.
Percent of change of the mean frequency and pulse rate of Northeast Pacific blue whale calls.
The percent of change is shown for A calls each year from 2006 to 2019 and for B calls from 1963 to 2019. Data in black are from the current study and data in red are from McDonald et al. [1].
Fig 6.
Mean frequencies of Northeast Pacific blue whale B calls.
Error bars represent 95% confidence intervals for mean frequencies at 10th second of the 3rd harmonic of the calls. Data from McDonald et al. [1] are shown in red and data from the current study in black for (a) 2006 to 2019 and (b) 1963 to 2019. The dashed red line represents a linear fit to data from McDonald et al. [1] and the dashed black line represents the quadratic fit to data from the current study.