ARK's base taming speed on PC, PS4, and Xbox is now doubled, meaning 1× is as fast as what 2× was previously. Dododex has been updated to reflect this. Use the "presets" dropdown for common multipliers.
For full Karkinos taming details, get the taming calculator app.
To knock out a Karkinos, aim for its abdomen. Hitting its limbs will only inflict damage and not torpor.
Put a catapult on a paracer, bring a high health turtle (carbomemys), whistle attack with the turtle and when the crab hits it put it in passive so you can easily aim and hit him on the body. No weird engineering needed.
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)
No one seems to have mentioned that karkinos can use tools, they just need a special type of tool: doedicurus, use a karkinos to pick up a tamed armadillo and walk around to rocks and the armadillo hits the rocks and keeps them stored, argies and quetz can do it to but they can only hold one and they don't spawn on abberation, not sure but if you transfer a beaver to abberation you might be able to use it and an armadillo at the same time to gather both rock and wood
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.