Whale Swimming - Wildlife of Japan

Discover the Magic of Amami Oshima’s Sea Amami Oshima, a UNESCO World Natural Heritage site, is a diver’s paradise. In the southern part of the island lies Setouchi Town, where the Oshima Strait—nestled between the main island and Kakeroma Island—offers breathtaking views of its rias coastline and crystal-clear waters.

Views of the Oshima Strait (Aerial drone shot by AquaDive Kohollo)

↓↓　Watch: How the White-Spotted Pufferfish creates its Mystery Circle

↓↓　A chance to swim with Indo-Pacific bottlenose dolphins in the Oshima Strait!

The Mystery of the Deep

Since around 1995, mysterious geometric patterns, about 2 meters in diameter, were discovered on the sandy seabed of Amami. These became known as “Mystery Circles,” and for 16 years, no one knew who created them.

The ‘Mystery Circles’ of the seabed that remained a puzzle for many years

It wasn’t until 2011 that underwater photographer Yoji Okata finally caught the artist on camera: a tiny pufferfish! In 2014, it was officially named the White-Spotted Pufferfish (Japanese name: Amami-no-Hoshizora-Fugu).

Later, it was discovered that these pufferfish live not only in the southern part of Amami Oshima, but also along the northeastern coast of Kakeroma Island and in the sandy depths of Kasari Bay in the north, at around 30 meters deep.

Japanese name : Amami-no-Hoshizora-Fugu アマミノホシゾラフグ

The name Hoshizora means “Starry Sky.” It comes from the beautiful white spots on the pufferfish’s back, which look just like the glittering stars in the clear night sky over Amami Oshima.

These Mystery Circles are actually spawning nests built by the males. Despite being only 10-15cm long, the male spends 7 to 9 days working without rest to dig grooves and create ridges using its fins. The more perfect the circle, the more likely he is to attract a mate!

When a female arrives, a unique ritual begins: the male gently bites the female’s cheek. This stimulates her to lay eggs and keeps her steady in the center of the nest. Once the eggs are laid, the devoted father stays for about a week to protect them and fan them with fresh seawater until they hatch.

Observing the Pufferfish (Photography by AquaDive Kohollo)

On our diving tours, you can observe the entire process, starting from the circle-making itself. If you’re lucky, you might even witness a female arriving or a male devotedly caring for the eggs. However, please note that these mystery circles are usually found at depths of around 30 meters, making observations difficult if they are located any deeper.

When observing, we take great care not to disturb the pufferfish or kick up any sand. While using a strobe is currently permitted, there may be restrictions on the use of continuous lights. Please be sure to follow the specific rules set by local diving association.

More to Explore

The Oshima Strait is a treasure trove of marine life. Beyond the pufferfish, you might even have the chance to swim with Indo-Pacific bottlenose dolphins! You can also find rare creatures like the Sutsubo-sando-yadokari (a hermit crab discovered in 2017) and the colorful Boxer Crab.

This hermit crab, called Sutsubo-sando-yadokari, was only just described as a new species in 2017. What makes it truly unique is that it carries and walks around in a ‘living coral’ instead of a shell.