I understand that all the previous tips submitted were useful, but just in case it was not clear, hit the TOP OF THE CRAB, it will have a special animation if you hit it in the correct spot, and will take only a small amount of boulders to tame, even a high level. (Irrelevant with Cannons)
The Karkinos is a massive crab-like creature in Ark: Aberration that can grab and smash creatures and players. It can also throw them at great lengths. Using its strong legs, the Karkinos can leap to impressive heights.