Hey Russh have not tried spear fishing from my sub , but have fished with a line.
Spear fishing up here would work, one of those long spears not sure about the gun, quite often see big fish (Barras, trevors, queenies, no not victorians), huge mud crabs that would be fairly easy to nail , they come in close in huge numbers up in the shallows at certain times of the year.