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 up/vo/te so people can see
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!
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
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)