Looks like some riveted sheet metal has washed up down under .
If this search fails then they are bringing in more powerful sonar ,
um why not get it now ? UNless it is being prepped , repaired , upgraded or retro fitted .
The Navy HAS very bad ass ROV subs and sonars just sitting and being maintained by private corps . Dont know the operating range on Magnatometers but gotta think they would help too