As far as those schooly mahi around the boat, really light line and a real small spoon is hard for them to resist .Especially if you can aim a small spray of water
behind the boat .Drop your spoon right in the spray. It mimics the sound of
baitfish / fish feeding and triggers a feeding response. [top secret ,don't tell anyone]
As far as trolling for pelagics [ tuna, mahi, wahoo ect] try to drag a lure that has a good contrast with the sky .Darker colors on clear day ,neon and bright on cloudy days.
When flying fish are in the area ,a trolling Bird lure with a spoon tied 4 to 6 ft behind it works great and is fun to watch too.
As already mentioned, Cedar plugs ,jet heads, all work great. A little wire leader your choice of hook and a 3 "-5" plastic straw will make a lure too .
As far as speeds , 3kts to 16kts will catch the pelagics .
I ran a fishing charter
and learned what would work. We used to bring the big fish off the bottom and behind the boat with the spray from the washdown hose.
You could sight cast to the one you wanted from there.
It was a lot of fun.
Calling fishy fishy fishy is also a MUST.