Make a taming pen that is at least 6 fences high so they can't jump out then go around the swamp with an argy. Once you find one Lure it out of the water then pick it up and throw it into the pen. And since you can shoot crossbow bolts through the fence it should be easy to knock out. Just don't let it pick you up in its mouth
Need one? Say no more, shoot with knockout arrows, bring atleast 50 because they live in a place with alot of other creatures,step two, lure away from swamp so it doesn't get killed by a sarco or piranhas ,step three put in meat and protect with life.