Original List from @wifeywubs, added Alter Offerings and Rarity, cleaned up the Seasons, Locations, Time of Day and Weather for easier filtering.
The Critter list is still under development by the community as the map is not easily segmented. The critter list on the Wiki is a copy of Unpause asia's work here https://www.unpause.asia/2023/10/coral-island-the-complete-ocean-critters-guide/ however it does not perfectly align with the community work to name and map the ocean found here https://coralisland.fandom.com/wiki/Diving?file=Diving_Map_with_Spawn_Zones.png. I've aligned them as best as possible.
Find Wifeywubs original list here: https://listium.com/@wifeywubs/89177/coral-island-critter-checklist.