SOT could do well with more ambient sea-life in my opinion. Things like a pod of whales surfacing before diving, an octopus clinging to the hull of your ship before dropping back into the water, dolphins following you as you sail, or seagulls simply hitching a ride on your mast could add some depth to the whole "sea" part of Sea Of Thieves.
If anyone's worried about this not being "Piratey" enough; fun fact, pirates were actually some of the first field-scientists! Back in the 17th Century, Pirates were often hired by naturalists to document animals they spot on their journeys. I feel like you could easily translate that to a "Field-Guide" mechanic that you could acquire from an NPC. Once you acquire an empty Field-Guide, you can slowly "discover" species and add them to it, slowly filling your book.
It'd be a fun side-quest in my opinion, as it's something you could do whenever, even during other missions. It'd also give SOT a reason to have animals that players have wanted in the game, but wouldnt have had a reason for including.
