They can be down deep. When I lived in Perth we used to get them out of 15 or so metres in the Swan at certain times of the year. Some of the commercial crabbers up Hervey Bay way deliberately only work deep water with big heavy pots - stops a lot of crab theft as most recs don't get that far out or have a pot hauler. Don't chase them too much any more myself since dilly's were banned but mainly used to work 2 to 5 metres back then.