Have you fished for GT's before Nathan? They're generally fairly predictable as to where they hang out, the Whitsundays will be full of likely spots. The majority of our fishing is based around Islands, as will yours be in the Whitsundays.
Focus long casts against areas with waves breaking/whitewater that is breaking over points or even better - bommies situated just off the island. If these areas have current running past them then even better. With the current running try to concentrate on the leading edge of where the current is hitting the structure, the GT's will often sit in the pressure wave at the front of these areas. If you can combine it all and can work you lure out of white water/eddies and through the area of current then you really are in with a chance. The general consensus seems to be the more water movement (current) the better.
I attached a quick picture of a random spot I picked in the whitsundays on google earth - i've never actually fished there but circled a few likely looking spots that I would try. The red indicates current and green is where i'd have a go if the current was running that way. (PS if that cloud at the top centre was actually a bommie it'd probably be the first place i'd go
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