The Japanese Encyclopedia indicate that Shibushi Bay used to be called Ariake Wan.
Searching Ariake Wan turned up this site:
This page presents the geographical name data for Ariake-wan in Japan, as supplied by the US military intelligence in electronic format, including the geographic coordinates and place name in various forms, latin, roman and native characters, and its location in its respective country's administrative division.
https://geographic.org/geographic_names/...60&c=japan
There is also this site - 1903 Maritime Survey Map
https://library.ucsd.edu/dc/object/bb2833973h
So far, unable to determine when the name changed.