I do not normally associate myself with set- setters, but was speaking to one once who claimed to catch Lemon fish inside the Wairau estuary in his flounders nets. But many people confuse Lemon/Rig with Dogfish.... Plenty of Red Cod in the Estuary over the winter months.
Have not surf fished there myself for many years.
Snapper do also enter estuaries and go a surprising distance upstream, you might even catch yourself a Westcoast Line Wrecker, a Buller Bull or even a Orowaiti orangutan while fishing there. but you would have to use your rod stand in the correct direction, otherwise they would just laugh at you while ignoring your bait. Its probably the reason why you blanked on the current trip.