If you need to do work underwater (I used this when building bridges between all of the islands) then, at least on mobile, you can go into camera mode by swiping from the left side of the screen. THIS PAUSES THE GAME!!! You can use this to check for megs before diving in the water.
I had a megalodon called jaws once, and I put him on wander to mate with another megalodon I had, but I forgot I left him on aggressive and he went after a dodo. He got beached and eventually about 4 dodos ganged up on him and pecked him to death. By the time I was there it was already too late. RIP JAWS ~ death by dodo
Killing these guys are good for leveling up if you want to level your kaprosuchus, sarcosuchus, or baryonyx. That's what I do. My sarcos hit for about 300 damage each and they can take on a squads of megalodon with ease.