I'm an old hand at catching serpents by now… it's quite easy since my wife does all of the chopping while my only task is to throw it and drag them onto land. Easy peasy.
Well, the mechanics have changed in the most recent update, and it took a couple captures to get my head wrapped around it. Especially since this is the first time I've lost a serpent (while harpooned) in well over a month!
Simply enough, while they're moving towards you such as attacking the boat or chasing you to do so, you expend no stamina maintaining the line. BUT if they attempt to move AWAY from you, you spend it like it's going out of style!
Speed of the boat doesn't seem to have much impact as I noticed the same high rate of stamina drain from full sail with a good tailwind to nothing but turning with no forward speed (not even rowing) while trying to land. Jumping in the water doesn't break the hold, but getting wet will obviously hurt stamina all the more. Hell, I had to chug a potion during a 15s trip from when I harpooned one to landfall and still lost it… though I was able to take a couple parting bow shots and kill it since it had already been hacked up pretty badly. Lost a sweet trophy though 🙁
The upside is that you'll see some absolutely hilarious mechanics dragging non-aquatic monsters, especially through water… such as the dumbfounded troll from last night who just wanted to go home.