This guys are a bit of a pest, all the more while taming in the open waters. Use a strong melee weapon to slay it fast. A good enough sword can be obtained after completing the Hunt: Terror Birds pursuit.
Not even worth trying scary do not think it doesn’t see you I was just wondering through the water trying to get to one island to another I always check the water before I swim once i make it I chase a titanosaur and boom a megalodon shows up do not swim
Use a high level Basilosaurus with high health to lead it to shallow water where the basilo gains health faster. Dismount and let the megalodon bite at your basilo while you traq it. Tamed 4 150 megalodon with this method works like a charm.