Pretty easy to tame. Trap it in a circular form of stone Dino gates, place catapult low if catapult is high the crab will die. Then shoot it with a catapult. Cannons insta kill the crab, do not use cannons
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)
Net projectile works on these, so craft your catapult and boulders, find your crab and net it. Proceed to set up the catapult a few feet from its face and you can easily just fire all required shots before the net expires. You’re welcome!
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.
You can tell if you shot the legs if it throws it’s arms up in the air when you shoot. If it doesn’t move at all when you shoot that means you shot it correctly, so make sure you don’t get it to throw its arms up when you’re nocking it out
Handy trick, if you're playing on Fjordur and want a high level DO NOT go to the Aberration Cave. There is a second Aberration cave near the Vannaland (South) Southeast teleport. Go inside, and if you find a low level kill it and harvest the corpse. Then do a lap of the cave (make sure to fight stuff to slow you down as if you run too fast this doesn't work), and you should have another spawn. I used this trick and in 5 minutes I had already killed 7 Karkinos, and they were a mix of levels. This is also a great way to farm Organic Polymer. Hope this helped
People were commenting boulders are better than cannons for taming these so I just assumed they meant rock golems. Kind of went out of my way to tame one. Doesn't seem to work for this but eh, I got a golem now. Lol