A couple of safety notes should be added. Every tuna is an individual, and where the hook ends up influences how the fish acts. Yellowfin hooked in the upper jaw by the snout are notoriously squirrelly. You have to be prepared to react to the predictable and unpredictable, and that often means getting out of the harness.
Use S-hooks instead of clips to attach the harness to the reel lugs so you can get out quickly if necessary. And remember to back off the drag (gradually, don't dump it into free-spool) when you need to get the rod out of the gimbal pad for maneuvers such as keeping the line out of the props.
When you sit back and put on a lot of pressure, a fish will often run out high in the water column. Enjoy the fact that now the fish is on the losing end of the energy equation. This is the only time you can take a breather. When the fish stops, bear down on it. Try to get a turn on the handle, going to low gear if necessary.
Step Up the Game
Tuna will often respond to the pressure by diving in the direction of the boat, which provides you the opportunity to win back a bunch of line with no more effort than turning the handle. Be ready to go into high gear when the fish sounds, and take that easy line.
Once the fish goes into the final stage of the fight - straight up and down - it's time to really put on the heat. Stay in one spot and keep the rod straight out from the rail. The tuna's tail beats are reflected in the pumps of the rod tip as the fish circles - the more pressure, the tighter the circle. The tip of the rod will come up as the fish leaves the inside (closest to the boat) of the circle. That's when you get those precious feet of line with several quick turns of the handle to bring the tip back down and keep the fish moving up. Don't waste energy by stubbornly trying to turn the handle when you stop gaining line.
Most important, stay relaxed so you reserve the burst of energy and sharpness of mind that is usually called for at the end of the fight.
Sometimes, a truly mean fish will say to hell with this and bust a big move. The telltale is an irritated shake of the head. You have to be ready to respond and follow. It's usually over soon after that - one way or another.
About the Author: Rich Holland of www.sportfishingreport.com has long been a top saltwater columnist, writer and editor on the West Coast, and has fished yellowfin tuna from long-range boats and sport-fishers the length and breadth of the Eastern Tropical Pacific, including Clipperton Atoll, Puerto Vallarta, Cabo San Lucas, the Revillagigedo Archipelago, Hurricane Bank, Alijos Rocks and Hawaii.