Chunking is taking dead bait, cutting it up and releasing a slow and steady stream of chum. You don’t want to overfeed, but have enough to get the tuna to come up to your chum slick. Be sure your hook baits are larger sized so other fish won’t take it. Have enough slack in your line so the larger bait drifts down through the column of chum. Keep trying different things to see what works. Cut the bait up in different sizes, skin on and skin off, changing your presentation. You never know what the tuna will take to on a particular day.