You clicked here because you believe that it is a god given right to pluck a creature from the sea and eat it.
And you want to know how to find the biggest tastiest creatures am I right?
Lets rap about it.
I have a spearfishing rig (1.2m gun with 2 heads - a 3 stabber prong and standard maki point) and a telescopic fishing rod that can handle about 5kg worth of fish.
Spearfishing is fucking badcore and as long as you can manage to aim correctly you caught a fish. No real tips there beyond common sense.
As an Australian we have a whole lot of great esturary fishing to do; my biggest tip would be to seek the habitat. Big fish hang out in water with some depth around reeds, jetties and other coverings - and use local bait. I cannot stress local bait enough. Putting a bug from nearby on my hook is 10x more effective than some greasy prawn.