Once found a Megachelon, search for a Microbe Swarm in it's premises. draw the swarm to the turtle and swim under it until taming starts. the level of the swarm seems to effect taming speed, effectiveness is always 100%. multiple swarms seem to be possible to shorten taming time even more. salmon bites reset taming completely! once taming starts leave it quickly by moving out of render. tribe log will inform you about finished tame.
They have patched the render range range so ignore any tips that say to leave render as it will no longer. Guess I’m stuck with the turtles I have, I’ve spent three hours trying to take one of these things and had it walk out of the water which reset it taming! It was at 80% that time. Never got it above 20 after that. What he for the saber tooth salmon that spawn to kill the swarm if they bite the turtle it resets to zero and you start over. Extremely frustrating way to tame a creature. I would like to beat whoever came up with this idea.