Does anyone know how the megalodon shark in the game is generated?

There is a very very very long explanation of meg hunting that would have a lot more specifics that would be helpful for very serious hunting.

But in general for the casual hunter as of this post. (Updates and patches have and can have significant impact on hunting over the years).

You want to aim for about 5 in game days in a session.

You might get one much earlier and you might get one much later but aim for 5.

There is something I'll call a change delay. If you dive or if you sink or if you merge they will add on about 1 in game day or so to your overall timer.
So if it happens on day 4, you might have a meg around day 6. Multiple dives or sinks or merges can slow it down quite a bit or might not be too bad. Stuff happening is just gonna happen so don't stress over it.

What you do after you kill a meg is just preference. Sometimes it's worth it to hop and start again, sometimes it's worth it to wait 2 in game days to see if you get lucky, and some servers just offer consistent 4 day megs. This isn't super casual friendly but it is a big part of my approach.

It's a time consuming thing but if you have any other specific questions about strategy I am here to help.

The difference between no megs a day and 8 megs a day organically is just time, experience, and luck. Time spent is really the only thing in your control, experience adds up over time, luck is just luck and a few dashes of sea karma.

If you do it enough it just becomes second nature to get a read on a server or situation. The type of meg is just rng but the spawn itself is a hunt, a good one and a rewarding one if you allow it to be.