Hi Rob
I have occasionaly seen tarpon on the edge of Heavenly bay, around the rocks, but a long way beyond casting range - even with your metal lures.
If you can get along the rocks (watch out for the occational swell on a rising tide) you could find barracuda lurking around. There are some stingrays which hang around the big bay and would doubless take a bait, but you would get lynched by half of the forum members for even thinking about fishing for them
Your best bet is to walk along big bay and try towards the rocks at the end. I have heard of bonito coming in on evening tides and blitzing baitfish, but have never seen this myself.
You might try getting out with some of the local guys if you fancy fishing around the rocks and you don't mind fishing from a working fishing boat without any safety devices. Ask around at the fishermam's co-op on the beach. Rusty has a good grasp of fishing with rod and line for cuda, kingfish and tarpon, but most of the posse will be able to take you trolling or casting around the bays and points towards Celery bay.
For a more formal and safety concious experience, especially for a trip to the sisters, then look no further than Alibaba Tours or King David Tours.
They both work out of Castara, so you will have no problem in finding either of these first-class operators. Just look out for their telephone numbers posted on telegraph poles in and around the village or just look out for the two biggest guys with the biggest smiles and the best kept boats.
A couple of reviews here -
http://www.mytobago.info/reviews/alibaba_tours.php
and
http://www.mytobago.info/forum/viewtopic.php?t=3530
Cheers
Steve