We used to "yabbie" all the time from our dams.
A bit of rabbit on a piece of baling twine, thrown into the dam for 20s, pull on the baling twine, and grab him by the tale (you have to be careful, a large one will remove your fingers).
They are quite tasty, but not all are big, the largest one I have caught was around 10inches in length. I don't know why/how they get so large.
Thier claws are the best eating.
Crawfish are located in the clay soils of Texas. Any place that stays wet. Creek beds ..etc. Use kite string with some bacon tied on end and dangle it in mud holes. They grab on and you have a crawfish. Some are very large. Used to tie them on little parachutes and send them up to our kites. Yank the kite string and down they float to the ground. We would then take 'em back to their water holes to be caught again. Then there were the times we would lauch them on top of tin cans. One can fit into another with water in bottom can and a chery bomb in top can for power. Ka Boom ..Off they would go.. with parachute tied to them for a soft landing. They earned their bacon.
It does seem odd to me that in parts of the world that SHOULD have similar climates I have seen nothing about it. All other things being equal (temperature and so on), I would think they should be the same size everywhere. But they don't seem to be.
It is as if there were something special about Australia - almost as if there were magic or some similar force at work...
That thought tends to go off the deep end though. There must be some explanation.