Hello friends. Very interesting topic you have here. You can model the electrodes underwater as an capacitor in parallel with a resistor (a leaky capacitor). Maybe this is why he used a bifilar coil... Bifilar coils are self resonant coils because of their capacitance. You can see this article here:
The autor proposed a resonant tank circuit without the capacitor, using only the capacitance of the bifilar coil.
If the electrodes underwater behave like a true capacitor, he wouldnt need 2 coils... Only one coil would do the job..