Pacer with platform saddle worked pretty well for me

Tranq Arrows/Darts DO NOT WORK!!! To knock this out you need to use a catapult and shoot in only on it's back. If you shoot it on it's legs it will kill it.

@Stormwebb19

Cannon balls discrease taming effeciency significantly! So for high tame level, always use boulders. Please let other people know! :)

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

If you are missing with your catapult and it's dying, drag dino corpses to it and let the karkinos eat the corpses. It will heal him up a lot then try again with the same torpor you left off with.

This tame is like the Rock elemental, but do not shoot it in the head. Shoot it right in the back of it's shell. Anywhere else will kill it fast.

To the guy who said "rare on floaty islands on crystal" that is a load of crap found 20 on 1 ISLAND!!!

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)

Using a cannon will ko any level crab in one hit, but will SEVERELY drop taming effeciency. If you want one quick, use cannon. If you want a high level use a catapult (the inferior siege weapon).