Article Acoustic characteristics of underwater tail slaps used by No...

In comparing Northeast Pacific Bigg's killer whale impulsive sounds to the sounds of Norwegian killer whales foraging for herring, I noted:

1) The right-hand vertical axis of figure 4A should be labeled "Source level" not "Received level"

2) The scales of both vertical axes in figure 4A are fishy. It doesn't make much sense for either the received level or the source level to equal zero where indicated. If this is a plot of received level (usually computed as the root mean squared value of the calibrated amplitude), then there should be no negative values in the time series. I suspect, instead that these are wave forms with the axes attempting to annotate the similarity of the *source* levels (for both shrimp and KW pulses) near 185 dB re 1 uPa @ 1m (RMS, presumably averaged over the same period centered on the pulse).

Finally, I value figure 4B, but would be very curious to see a comparison of the spectra for each pulse within the "multi-pulsed structure" of the tail slaps. Listening to them in the supplemental material, my ear is convinced that in some cases there may be some initial cavitation, but subsequent pulses are most likely impacts between the fluke and individual herring. Why not compare those two types of sounds with should have very distinct wave forms (due to initial pressure deviations being opposite)?