Very easy tame buy in a dangerous place when found in a swamp. First make sure the area is clean of mobs like snakes etc etc. Next start tranqing and kite it. They are really slow and turn slow , so it's easy to kite them in a circle. Once it's down , gather or use wooden spike walls around the sarco to ensure that it doesn't get Aten while knocked out , I usually always starve tame to make sure I don't lose any kibble or meat like mutton. I actually love my sarco , I use him for underwater drops until I get a mosas. Jack of all trades , fast in water with unlimited stam, tanky especially with a good saddle and can go inside underwater caves. You can also use a GPS or weapons which as a cross bow on the sarco too, making your first big underwater tame much easier and you don't need a water Dino pin for these guys.For getting pearls and deep sea loot crates level nothing but health. They get ALOT of health per level and can get 8k pretty easy.
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 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