Blackfin tuna tend to be on the small side compared to yellowfin tuna, but when you find one you often find droves and they just love hanging around offshore rigs. Added bonus: this is a “white meat” tuna, and its steaks are hard to beat on the grill. You’ll catch some by accident when trolling around for yellowfin, but if you really want to bang on blackfin try live bait chumming for them.
Step one is filling the livewell to the gills with baitfish. Any sort will do but you do need big numbers, so throw the cast net or fish sabikis until your arms are aching and you have as many aboard as you can keep alive. Then go to a rig where you’re fairly sure blackfin are present, and get a scoop of baits out of the livewell. Cup the back of your bait net with one hand, and hurl those poor little guys at your outboard cowl or the back of the transom. The idea here is to stun them. You know how stunned fish swim in pinwheel circles? That’s ideal, it’s a loudly ringing dinner bell the blackfin can’t resist. Repeat the process three or four times until there’s a trail of injured fish leaving the boat, and those that are unharmed begin to school around it.
Now hook a bait through the lips or eyes on a rig with a 6/0 to 8/0 hook, on 30- or 40-pound fluorocarbon leader. Don’t add any other weight or hardware. Drop it back, and leave the reel in freespool so the bait drifts off as naturally as possible. Then grab another scoop of bait and keep the trail of free dinner coming. When the first line is 30 or 40 yards back set a second line, and so on, staggering the distance each line is set at.
At some point when the blackfish start spotting the pinwheeling fish you’re likely to see explosions going off behind the boat. If your baits don’t get smashed try to judge how long they’ve been drifting back and whether or not this one or that one could be beyond the school of tuna. If you think one may be, reel up and redeploy. If, that is, you have the time to between the other baits getting eaten!