Just keep a slight distance away and shoot narco arrows into it's head. If you upgrade your movement speed some (idk how much exactly), you could just keep walking backwards to keep the sarco from reaching you since it never runs on land (at least none of them ever did for me).
I recommend taming them when you are at a level that can craft tranc arrows.I DO NOT RECOMMEND TAMING IN WATER THESE GUYS ARE INSANELY FAST IN THE WATER.Dart them then lure them on to land then back up tranc back up tranc and you’ll have a new buddy (Get a chef station at lvl 23 for 20 amber) Craft some trike kibble for a faster game.
I recommend taming one, they are super fast in the water, and they do a LOT of damage. I have tamed carnos and therizos but my one Sarco is the strongest one, I easily killed a megalodon and mine is only level 25, I only leveled up the stamina, speed and melee strength. Knocking it put is easy, just get it to follow you on land then throw some tranq arrows or darts to knock it out and feed it raw meat