Can be found in Arsha Sea by lliya island for this quest http://bdocodex.com/jp/quest/4520/191/

http://imgur.com/YKiUGAo

Can confirm that it is harpoonable in every sea zone that is not Ross or further north. Keep in mind that you sometimes can't harpoon because you're too close to shore or bugged char. Check the dura consumption of the harpoon to see if it works. Only other ppl can visually see if your char is bugged (glitching back and forth). Then you need to go char select and back. Happy harpooning :3

Is it necessary to use fishing boat when I want to harpoon?

Pesca com Arpão entre as ilhas de Teste e Ilha de Daton ao Norte de Epheria
https://prntscr.com/rtsfq2

Many times i can't harpoon due to ocean waves being so large i clip through the fishing boat. Going to character select and then back almost always fixes that. Now that said, i can't find the Sperm Whale anywhere. It's not on Famme's map. I have tried Arsha sea as posted here. I have also tried Ross Sea and Epheria Sea as well as Ahrmo sea in that screenshot from Xenogames. In all the time i had done Harpooning for other quests i had never gotten one either. I have never seen a NA screenshot or video of a Sperm Whale and i play on the NA servers.

Atrapé uno en un spot de pesca cerca del Archipiélago de Cron. Según comentan arriba otros jugadores, se puede obtener el Cachalote de cualquier spot de pesca, con el arpón... pero toma tiempo y suerte, porque son peces con muy bajo porcentaje de drop.

3 saat sonunda Luivano adasının sağ tarafındaki 4'lü adanın ortasında yakaladım. Üçüncü saatte eşya düşürme parşömeni açtım, yakaladım. Alakası var mı bilmiyorum. Yaşam becerisi 865 - Guru 18 balıkçılık.

https://ibb.co/vsMZ1P3

It appears that you can harpoon them easily just south west of Kuit/Padix island. Apparently can make a good session on 20 of them there.

Also, update from July 2023 : spot between Illya and Ajir island still works but it took me an hour with 1300+ mastery

got it today on NA region
https://imgur.com/a/8Qwx4BR
wasted 2 blue harpoons
900 Mastery

Finalmente, o local foi entre a ilha de Iliya e a ilha de Ajir, tem que cuidar pra ficar na parte mais profunda, perto da costa não fisga, servidor SA
Your text to link here...

3 4 Saat lliya adasıyla - Ajir adasnın tam ortasında durup yakalamayı başardım.

Titres :
Amateur de Cachalots. (32)
Prince des Cachalots (142)