What happens next?

How to gaff a tuna
Keep the boat heading straight, at a low speed.
Once a member of your fishing party has caught a tuna on the line, slow the speed of the fishing boat and don't make any unnecessary turns. This will make it easier for the angler to reel in the tuna.
If the boat accelerates or makes sharp turns, the tuna may break the line or slip the hook. Under these conditions, the tuna should swim up alongside the boat and present itself for gaffing.