I have no doubt that the Saanich inlet crabs have a taste for prawns, but they seem to work great elsewhere as well. I put my one trap down today for a four hour soak near Sidney island and got 9 jumbo dungees and one female bursting with eggs, first time I've seen that before. It was only me in the boat, so just took my limit of four males home for a family feast. My neighbor had 2 traps down in the same zone....and got one rock and one dungee. Only difference was the bait. Prawn heads have performed well for me off metchosen, oak bay, Sidney area, etc.
It helps to give them a bit of a crunch before freezing to get the juices(brains!) going. Then when they thaw out the scent really spreads. Certainly not as good results if the heads have gone off at all so you have to freeze right away.