Yonaguni
Japan · Ryukyu Islands
Yonaguni is Japan's westernmost island, famous for the Yonaguni Monument — a controversial undersea rock formation that may or may not be man made — and a winter hammerhead shark aggregation. Cold-water diving with Japanese precision.
How this reef is doing
ⓘ How we measure thisReef state
Submerged stone monument is the headline dive — not a coral cover destination. Hammerhead schools Dec–Feb.
Coral cover
Fish life
Heat
Warmer than usual right now, but not hot enough to bleach.
Fishing
Protected on paper, but boats are still busy nearby.
Sources · MERMAID and partner coral surveys · NOAA Coral Reef Watch · Global Fishing Watch and reef gravity
What you will see
9 species across the dive sites here
Scalloped hammerhead shark
Seen 3 months ago
at Yonaguni Monument
Critically endangered
Dogtooth tuna
Seen 4 months ago
at Hammerhead Point (Irizaki)
Least concern
Bigeye trevally
Seen year round
at Hammerhead Point (Irizaki)
Least concern
Giant trevally
Seen year round
at Yonaguni Monument
Least concern
Great barracuda
Seen year round
at Hammerhead Point (Irizaki)
Least concern
Green sea turtle
Seen year round
at Yonaguni Monument
Least concern
Whitetip reef shark
Seen year round
at Yonaguni Monument
Vulnerable
Yellow-spotted boxfish
Seen year round
at Yonaguni Monument
Indo-Pacific sailfish
Rare sighting
at Hammerhead Point (Irizaki)
Vulnerable
Dive sites
What divers say
Whether the monument is natural or built, swimming over those right angle terraces with hammerheads above is unforgettable.
Good to know
Water temp
16–22°C in winter — 7mm or drysuit recommended.