I tamed a low level one only level 4. Seems that evwrthing hates tamed Megaladons. It got swarmed by 3 other megs and 2 Mantas. Lost it within a few minutes of taming. Your better off with a Sarco if you intend to stay near the surface
I also saw another person say this just get a itchysouriour and I know I spelt that wrong who cares they look like a dolphin anyway put a saddle on it and kite the megaladon I thought of this while I was taming one
Megalodon have quite a big turning circle. Pump movement to at least 120% and go find one using a scuba suit, get next to it but a bit towards it's tail end, shoot with tranq arrows and it will circle round and round until its KO'd. Enjoy your new pet!
If your looking for a quick way to get across the sea. This is not it, their slow and stamina runs out fast. Believe it or not their very vunerable and other megs will still attack. Their turning radius isn't great either. Your better off with a Sarco.