Best trick i've used so far was hopping in a Karve. But it isn't as simple as fishing off the boat:
1. Sail up to a school of Fish
2. Cast the line gently, 5-10m is good enough.
3. Hop in the Rudder seat and start paddling backwards and turn as hard as you can. Thankfully it's possible to use the Rudder and a Fishing rod at the same time.
4. Keep doing circles, or keep turning as much as you can while paddling backwards, eventually fish will take notice of your bait.
5. Once the fish is on the line, sail into the fish while reeling in, and the fish will jump right into your hands with very little Stamina drained.

Once you get this trick down you can get stacks of fish in a day.