Damo,
If you're from Western Australia, there are a few anglers around from that state as well. I have spent quite some time and effort popping the north-west of WA, but the results and rewards (for me) have not been the most encouraging. You still hear of enough fish being caught to create a buzz, but it astounds me that despite the low population density and even lower general interest there is nothing that I would deem really 'productive' available in WA.
I don't mean to sound totally disillusioned but I have been to alot of places that people say are 'GT meccas' like the Murions and the Rosilys, and all I can say is that those people should go to New Caledonia or on a Nomad trip before making such claims.
However, there are still a few big islands that are reputed to be worth it for those keen enough to explore - these include the Monte's and the Barrow islands. Perhaps Bernier and Dorre may fall into that category. I think your challenge is doubled though, because while GT popping can be complicated enough, the importance of handling a boat effectively, both during casting and fighting, cannot be understated. While it is a whole different story, it nevertheless plays equal, if not more, importance than the actual rod-and-line fight if you want to land more fish than you lose.
The picture above certainly looks very 'fishy', but to start off first, you will need to identify some good channels, bommies, deep-drop offs and rips. Water depth is a very contentious issue, as you could find success in anything less than 5 metres and sometimes over 30m. I think this depends more on the environment than specific depth per se. For example, it could be a big bommie rising up from 10m to break the surface, with current swirling all around it. Or, it could be a deep drop-off that starts at 30m and rises to 10m, such that you wouldn't even see it from the surface.
I think you should give up if you fire 3 or so sweet casts in and raise nothing, depending on how big the structure is - as sometimes you can do a lap around it. If it's a bank do one slow pass and if nothing comes up don't bother hanging around. However, the tricky part is that just because a fish isn't there now won't mean there won't be one there the next time.
There is alot of info relating to tides, times and moon phase available already, and I'm sure other members will be happy to further expand on these points.
