Conversion between dBs referenced to the standard pressure of 1 µPa in any medium but air and 20 µPa in air is performed not merely by subtracting the 26 dB in difference as the authors would appear to have done here (in effect). One ALSO has to convert the pressure values into intensity using the values of acoustic impedance of the two media. Together (i.e taking into account both the differences in reference pressure and impedances) the conversion can be performed by subtracting 62 dB form the in-water SPL values.

If this indeed the case you must therefore subtract yet another 36 dB from your value. Doing so brings M. scholtzi back unto the regression line of stridulating animals.

I may be mistaken, in which case it is my opinion that the unit conversion is inadequately described.