I once was taming s lvl 130 of these. Took me 3 hours and in the end I ran out of food and the taming bar dropped back down to half after being at 90% I just didnt have the time and patience anymore so I killed the stupid thing and fed its meat to my ichy.
1. Get an ichthy with a saddle
2. Find a megalodon underwater
3. Kite the megalodon to shallow water with your ichthy
4. Tranquilize it from the shore or a rock safely
5. Make sure you don't keep shooting it after it is KO (I learned this the hard way)
6. Name it Bruce