Drac346

I'm running some tests myself.  There's a template override and the map override. 

Using the official server json:

The mermaids are in the map overrides on the official servers but the template overrides have the whales, squids, ect.  My guess is that you will not see any whales (template based) on golden ruins because the mermaids (server based) are loaded after the template overrides.  They aren't cumulative.

Load Order (assumption), Bottom takes priority.
Template
Server
Spawner
Island

If someone has tested this and can confirm, or update, the order; please do so.

These were recently added to the server templates in official map (with the map editor) dated 1/7/2019.

For example, if you look at the POLAR template, you will now find:

"(NPCSpawnEntries=((NPCsToSpawn=(BlueprintGeneratedClass'/Game/Atlas/Creatures/MeanWhale/MeanWhale_Character_BP.MeanWhale_Character_BP_C'),NPCsSpawnOffsets=((X=0.000000,Y=0.000000,Z=-700.000000)),NPCsToSpawnPercentageChance=(1.000000)),(NPCsToSpawn=(BlueprintGeneratedClass'/Game/Atlas/Creatures/MeanWhale/MeanWhale_SeaMonster_Character_BP.MeanWhale_SeaMonster_Character_BP_C'),NPCsSpawnOffsets=((X=0.000000,Y=0.000000,Z=-700.000000)),NPCsToSpawnPercentageChance=(1.000000))),NPCSpawnLimits=,MaxDesiredNumEnemiesMultiplier=4.000000)",

Squid is also there under desert.  Each of the epic ocean spawn is assigned to a climate in the official map.

"OceanEpicSpawnEntriesOverrideValues": "(NPCSpawnEntries=((NPCsToSpawn=(BlueprintGeneratedClass'/Game/Atlas/Creatures/Squid/Squid_Character_BP.Squid_Character_BP_C'),NPCsSpawnOffsets=((X=0.000000,Y=0.000000,Z=0.000000)),NPCsToSpawnPercentageChance=(1.000000),bForcePreventSpawnOnOcean=True)),NPCSpawnLimits=,MaxDesiredNumEnemiesMultiplier=4.000000)",

Use the Server (or map) overrides to add your mermaids. The mermaids are only on the maps with PVE islands (quest islands) if you follow the official map design and the override will probably remove the other critters (hence Override...)

Or, combine and mix to your desires.

I posted each of the individual spawner overrides from the official map in the walkthrough: https://www.drac346.net/2019/01/atlas-dss-guide-useful-tips.html

The guide linked above was replaced with a more detailed one:

https://www.drac346.net/2018/12/atlas-dedicated-server-setup-main-menu.html

Updated Full Guide for those that were using my previous guide.

https://www.drac346.net/2018/12/atlas-dedicated-server-setup-main-menu.html