The bug
Dolphins don't seem to be spawning in cold oceans anymore.
How to reproduce
Create a new map with a random seed, plug the seed into mineatlas.com to find oceans to teleport to. While in "cold" or "deep_cold" ocean, move around a bit in creative mode to get water mobs spawning, then run:
execute as @e[type=dolphin,distance=..200] run say hiIf there are dolphins within 200 blocks of you, you'll see them talking in chat.
In every other ocean type (except frozen) I get between 5 and 10 dolphins saying hi, nothing in cold oceans anymore.
Linked issues
relates to 2
Comments 7
Not according to https://minecraft.gamepedia.com/1.13/Development_versions
All it says is that they don’t spawn in frozen oceans, not cold. Also, the “biomes” entry on the wiki (https://minecraft.gamepedia.com/Biome) specifically lists dolphins as “features” under all aquatic biomes except frozen and deep frozen.
So which is right?
I referenced the wiki because it's easier to look up the changes, but the information is taken directly from the snapshot posts on Minecraft.net. It specifically says regarding dolphins, "spawns in any ocean that isn't frozen."
https://minecraft.net/en-us/article/minecraft-snapshot-18w15a
The spawning is intentionally limited to warm oceans.