They seem to have certain spawn locations. If you mark them you can farm them or avoid them, we have been farming them for meat.

They will spawn more at night and during a storm.

A Karve can only take about 4 hits... the longboat is what you want to use.

The longboat can outrun them with a good wind and full sail... they seem to stay in their territory and if you go far enough you can escape them.

A good bow and skill can take one out quickly. The meat will float but scales and trophies will sink.

With two people it is good to use the harpoon and beach them. Drag them on to land and kill them there to get all the stuff. They will not fight on land, only try to escape back to the water. Often it is too dangerous to land so at sea is easiest... don't want to drag one up next to a goblin village ha ha.

They are more likely to spawn at night.

They are more likely to aggro on you if you are going slow.

They also seem more likely to spawn during a storm.

That is what I have been observing so far, hope that helps.

https://steamcommunity.com/sharedfiles/filedetails/?id=2435798604