I discovered Deep-Sea Site 6, but I can't for the life of me see what zone granted that discovery.

[5:06]OompaLoompa attains rank 42!
[5:06]A new subaquatic voyage destination─deep-sea site 6─has been discovered!
But I don't see any record of that discovery in the voyage log. For the record, the course for that ship was Neolith Island --> Kanayama --> Deep-Sea Site 5 --> Concealed Bay