They would probably need to Sonar map the area from the surface before sending the Blue Fin down. So when the they decide to stop using the TPL-25. They will sonar map the area for sure with either HMS Echo purposely built for the job or an RAN ship which I'm not unsure if they are in the area. They Royal Australian Navy have I think 6 survey ships with 4 being hydrographic.
Surveying Ship (AGS) | Royal Australian Navy
Just looking at the Australian Navy website the 2 AGS vessels don't seem to have commanders at the moment so maybe they are in dry dock or servicing who knows. Or the website is out of date.
If that's the case the HMS ECHO will be it for sure.