There are three locations where Blue Whales tend to spawn:

Calpheon Sea – Seas of Banto, Seas of Peyon, Seas of Ahrmo, Seas of Olvia

Balenos Sea – Seas of Nox, Cron Islands

Mediah Sea – Seas of Arusha, Seas of Sausan

Below shows the possible routes the Blue Whale can follow.

Blue Whales [Group Hunting]

The Blue Whales are Hunting bosses that randomly approximately 3 times a day on each channel and have a chance to spawn 2 additional times after the initial spawn. A server message will be shown when the whale spawns and the whale will die naturally if it has not been killed within 40 minutes from the initial spawn.

It requires multiple parties of hunters to kill and only the top 20 damaging parties will receive loot. The whale does not stop moving and you will need a fishing boat or Epheria boat with one person to drive while the others deal damage. The driver of the boat does not have to worry about hitting the whale and they will receive loot at the end. I would also recommend using a fishing boat instead of an Epheria boat if possible because it is much easier to stay directly behind the whale and you’ll find you are able to hit it much easier.

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If you're asking for humpback Whales. I've included a map below. 

Sperm Whales are not in the game as of yet nor have I heard of them being introduced. I'm very into Sea content so id definitely be aware if they were a thing lol

Happy hunting and good luck!

[Sorces] [https://www.blackdesertfoundry.com/hunting-guide/ ] [urzasArchives.com] 

I wanted to include this as well, just incase. 😎😁🤠

its a list of sea critters you can encounter. 

These arnt hunting mobs like the whales 🐋 above but regular mobs you would want to use a ship with cannons for.

https://grumpygreen.cricket/sea-monster/

Sperm Whales are ingame and need to be catched with a Harpoon - https://bdolytics.com/en/NA/map you can enter here at fishing sperm whale and when it shows the regions you can catch it. It is very rare.