Since 1.8.0 update, squids became rare compared to previous versions.
 
When you login right after the update and dive in to the ocean, at first glance, there are many squids swimming around and looks normal. (They have spawned before the update)
But once I kill them all in around 128x128 area or more if you like, then you will see much less of them respawn. (feels ~20% compared to 1.7.0 in local world)
I tested in both local world and Realms, and it happens in both environment, but should be noted that the rate is excessively lower in Realms.
In my Realm, surrounding 256x256 ocean has respawned barely to none squids. If I go far enough to load newly generated chunks, sometimes I can find squids spawning, but in existing chunks, no more.
 
What I expected to happen was...:
When I kill squids around me and move away, they should respawn in low populated area.
 
What actually happened was...:
In most of existing chunks, once you kill them squids will barely respawn.
 
Steps to Reproduce:
1. Find an ocean biome.
2. Kill the squid all around you.
3. Move out from the biome then come back and check whether they spawned.
 
If I have some way to bring back previous 1.7.x version I would be happy to compare the spawning rates.