In my experience I have found a couple of ways of taking these big boys down easily. The first one is to utilise it's turning circle as it cannot turn fast at all, so hug it's back legs, turn with it and whack it with some sort of melee weapon at the same time, a sword or pike works best for this. The second technique is to just walk backwards and shoot it with something, preferably something damaging, so I wouldn't suggest using a slingshot here. But doing this back step technique will allow you to just be too far away from the Sarco's bite, however, be careful of what can come sneaking up behind you. And by all means do not try and out swim this thing, it will win, every time.
When riding on a boat keep an eye out for these guys because unlike most other water dwelling predators, sarcos can still see you and attack you on the raft. If it gets to you it will be hard to shake off the raft, it'll make the raft move buggily, and if you don't act quick it will ruin anything you're carrying on the boat, and can of course kill you, most likely leaving you're raft stranded. If you have a partner have them stab it to death, they are weaker than they look. If you're alone, try to get as close to shore as you can and fight it off there.
These guys are all over the swamp regions of the island, and their swift swim speed means they'll ambush you quite easily. Stay aware of your surroundings.
Take advantage of their poor turn radius and move to the shores so they move more slowly.
I tried and battled a sarco that lived near my thatch base once (I was a noob) and the thing killed me 5 times before making it unconscious though I didn’t think of taming it so for revenge I killed it it is also very slow so you can outrun it easily
don’t approach if you have a lot of weight on you. they’re slow enough to out-run with base stats though so if you accidentally get ambushed by one, you can run off. if you’ve run out of most of your stamina, you can attempt to jump onto a rock. eventually the sarco will abandon the rock and head back to where you found it.
These guys are not hard to take on land... my three low lvl dilos (4,5,7) took one down early game. I don’t know the level of the sarco because I was running away (I thought I was in trouble) but when all 3 of my dilos returned, one of them had a recipie, some arrows, and a sling in its inventory, presumably from the sarco.