I did a bunch of experimenting with trolling today. Had a ton of luck and got some good insights.
Sailing a karve I cast short 8-10m from the boat.
Once the bait is in the water grab the rudder and sail the coastline.
During the day you can visibly see fish as you pass.
Look for big schools of 5-10 fish in an area. Once you find a good spot, you'll easily be able to pull in a few, but I felt it more optimal to continue trolling rather than trying to catch all the fish in one spot. Unless there was visible Tuna or Pike.

The larger fish appear to like a faster moving lure. If I could see Tuna or Pike I'd give another lap around the area, trying to drag my lure through groups and/or as close to the larger fish as possible.
Fishing and sailing simultaneously took a little getting use to, but it was well worth it. When the lure hits the water you can steer the karve and real-in at the same time.
Once a fish was on, I would quickly adjust my direction (usually reverse) to close the gap between me and my catch.

Tuna (4 fish meats) appears to like deeper water (sudden drop-offs on beaches from Meadows and DF)
Tuna seem to be attracted to a faster moving lure. Full (3) speed karve gets their attention, but they'll only follow for so long. I found that adjusting speed down (2) coaxed them into biting.
Tuna will also bite in the open ocean, but seemed much more 'miss' than 'hit'.

Note: As soon as night fell, or a storm hit, I trolled out to ocean in search of serpents.

It did appear that most fish would not bite in the presence of enemies (or were much more reluctant to). I tested this both greylings and leeches in two big schools.

https://steamcommunity.com/sharedfiles/filedetails/?id=2726558124