1) no need to mark spots on your map. Ocean Biomes have a chance to spawn Serpents at night.
2)Chances are increased in bad weather.
3) Night spawned serpents will disappear at dawn
4) You can get serpents to spawn in the ocean biome during day time in bad weather.
These spawns will NOT despawn and will remain (day or night).
5) When you are in an ocean biome under "spawning conditions" (night time and/or bad
weather) Always keep an eye out behind you, slow down occasionally (even stop). They
don't always spawn aggro'd to you so if you blaze at full sail through a ocean block you
can often trigger a spawn w/ out seeing it.

Do not confuse serpents you encounter in the daytime and in good weather as proof serpents can spawn in daylight and good weather. They are simply serpents you have spawned earlier but did not see.


If you are interested in trophies and scales I flattened out this beach and populated it with 2 star wolves. I simple harpoon the serpent... beach my longboat, jump off and drag the serpent onto the shore and the wolves make quick work of him.

That pole in the center is lined with Serpent trophies.

https://steamcommunity.com/sharedfiles/filedetails/?id=2741035624