all of the above will help. I think being in a network of guys that are fishing for them will increase your odds and will give you the biggest value. you hope to gain from them is location because like reality location is almost everything. You must know the drop offs where the typically hold and don't forget these fish can go 30 miles an hour and they don't hang around if there isnt any bait in the water. These are musts for tuna fishing note that outriggers is not 1 of them.
Sonar 600-1kw
bathometric charts showing drop offs
4-6kw open array radar and your ability to adjust gain so that you can see birds working on the surface.
Birds will tell you where the fish are other than that you ight as well go out there and drop a hook in the anywhere and Tuna WISH.
also seeing whales and or dolphins can be a good sign too.