MAKE SURE and hit the crab in the top of its body, on the top of its back, anywhere else will kill it. Use a catapult and it should do an animation when hit in the sweet spot, pace your shots to about 10 seconds between each!
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. UP-VOTE SO EVERYONE KNOWS & TO GET DODODEX TO ADD THIS!!!