My crayfish traps are about 18“ square and 6“ high. The bait is placed in the bottom (fresh local fish guts, heads, skin). The crays walk up a ramp and fall in then can‘t get out. I tie it to the neighbor‘s dock and it sits on the rocks below. When the catch is good I go down and empty a couple of times in a day because if they pile up they can climb out over top of each other. I bring up the trap and throw back all the little ones, then look under the tails of the rest and throw back any with egg sacs. A day like that will get me 30 or 40 which is a nice feed. The bigger ones in my lake are just big enough that the claws are worth eating, but on another lake in the same system they grow bigger - langustinas!