Heihachi - far from Pro mate, but I do love the game...
Cracker - Mate I can only offer a little advice in this area as I haven't had enough shots on YFT with jigs... I can say a couple things which seem to be th trend in YFT jigging... here in the Cape, whats worked, as well as Internationally...
YFT to to eat smaller, flutter style jigs far more often than long spear jigs.... most guys are using flutter style jigs like Hooker1, our TW Slayers, and a couple other exotics like FLABo's and such.....
Unlike Yellowtail, AJ's and such which seem to prefer the faster slimmer jigs, tuna jiggers have more sucess on the flutters, worked slower and often even in a yo-yo motion, although slow medium mechanical jigging seems the way to go.
Depth... you need to get to the fish... Are you marking these schools? If so, I would guess 10 to 15 metres below the depth they are. Tuna will hit these flutters jigs on the drop, so be prepared for that.
What size are the fish? I think as Tuna are not fish to take you into the bricks, capacity is more important than strength or abrasion resistant... I would spool PE 4 to PE 6 line. That should range between 40lb and 60lb breaking strain.
Of course there are exceptions to every rule, so if one thing doesn't work, try another. What are the fish feeding on? Might be worth trying to match that either in size or shape.... natural colours probably best, or something similar to what troll colours work.
Sorry I can't be of more help mate,lets here back how it goes.
