Amami Ōshima · Japan · Sand slope · Muck & macro
Mystery Circles
Male pufferfish sculpt two-metre circles into open sand
A flat sand bottom off the south coast of Amami Ōshima where male white-spotted pufferfish sculpt circular nests two metres across. The fish has been recorded between 10 and 27 m and its structures at 10 to 30 m, and the circles are built and tended from spring into summer. There is no reef to follow here: the dive is a search across open sand for the sculpture and the fish that made it.
Also known as Amami Mystery Circle, Pufferfish Nest.
Where it is and how deep
No published position for this site — the map shows Amami Ōshima and its other sites; operators know the mooring.
The dive
You drop onto open sand with no reef or slope for reference, and nothing on the bottom tells you where a circle is until you are almost on it. It resolves as a set of low ridges worked outward from a groomed centre, roughly two metres from edge to edge. The pufferfish itself has been recorded between 10 and 27 m and the structures down to 30 m, so the profile is planned around wherever the active nests are sitting rather than around a fixed depth.
Each circle is the work of one male, which takes seven to nine days to plough the shape into the sand: it starts the outline with its belly, then raises the ridges by fin-waving along straight lines and radial passes through the centre, and afterwards stays near the finished nest to attract a female. Spawning runs from spring to summer, so that is the window when males are building and tending circles. Hold trim well off the bottom while you look, because a single fin stroke close to the sand flattens ridges that took the fish days of work to raise.
Background
Divers off Amami Ōshima began reporting circular structures on the sand in 1995, and for nearly two decades nobody knew what was making them. The animal responsible was finally identified and formally described in 2014 as Torquigener albomaculosus, the white-spotted pufferfish, which answered the question and gave the site the name divers still use for it.
Marine life and season
- Macro critters
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Fair | Fair | Good | Prime | Prime | Prime | Good | Good | Fair | Good | Good | Fair |
Season follows Amami Ōshima: The pufferfish nests are built Apr–Aug, which is also the calmest window; typhoons disrupt Aug–Oct and winter brings north winds.
Know before you go
- The bottom is fine sand and the ridges are fragile; poor trim silts the site out and destroys the nest you came to see.
Questions divers ask
How deep are the Amami mystery circles?+
The pufferfish has been recorded between 10 and 27 m, and its nest structures have been found at 10 to 30 m. The dive is spent on open sand at those depths rather than on a reef.
When are the pufferfish nests active?+
Spawning runs from spring to summer, so that is the window when males are building and tending circles.
Sources
- Torquigener albomaculosus — Wikipedia
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