Island society that hunts huge whale-like creatures I'd appreciate any help identifying this animated film. 

The main portrayal is of an island society that hunts huge whale-like creatures, using boats and harpoons. When a member of this society dies, he tumbles down an immensely deep hole, where he undergoes reincarnation into one of the whales. 

This film was from Japan and I saw it in the early 1990s, I think, on a VHS collection from some animation festival or other. It was in color and I do not remember there being any language in the film.
I believe Skywhales is what you are looking for. It is a British animated short film in 1983 directed and written by Phil Austin and Derek Hayes, and it is included in the British Animation Collection Volume 1 DVD.

You can view this animated short on Youtube.

A scene during the hunt, where the main character flew towards the skywhale and stabbed it with a harpoon.



The scene where everyone returned from the hunt. You can see a bunch of flying ships anchored on the port.



The main character died and went to throw himself down a hole inside a building.



As he dropped down the hole, he turned into cocoon, then emerged from it as a skywhale.



The characters in this animated film speak some sort of nonsensical language. You probably mistook it for Japanese.