Megalodon Spawn Mechanics

This is something Pirate Legends should be able to do. Buy a last seen location/rumour from the hunters call go there and play the song from the hungering one to get it to spawn.

Maybe a new species, turn in eyes, teeth and fin for rep.

Same with skeleton ships for the order of souls. Get a new skeleton captain skull. Both could be handed in for Athena rep.

I found hoarding loot and rare items tends to summon them in waves. :p
Or when I don’t want them to appear.

They spawn more often if you have loot, but this is also true with Skeleton Ships. Also, the spawn chance isn't base on the cost of the loot but the rarity of it, with the final reward item in a Tall Tale being rather high up on the list. So you could speedrun an easy Tall Tale real quick, get the reward item at the end, then just sail in open waters. I remember getting a Meg instantly on my empty ship just because I added Briggsy's skull to it.

I’ve noticed higher chances of spawns “up to two at a time” when sailing within close proximity of other alliance ships from location to location.

I’ve tried a ton of different things. The highest chance to get a meg, in my opinion, is to complete voyages. When doing a gold hoarder quest, every time you complete a chapter, your chance goes up to get a meg. When completing the whole voyage, tall tale, Athena, or fort/fleet, the chance is highest. However, it does seem as though the chances are reset after the kraken is killed . Or maybe just the meg types and locations are changed.