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Ogasawara operator page describing Tuna Cave (Maguro Ana) as a major dive point with large marine life.
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The site is normally reached on an organized expedition from Chichijima to the Keita islands.
Maguroana is a dramatic rock arch off Yomejima in the Ogasawara Keita islands, with a half-submerged opening and holes in the rock that draw tuna into the shelter of the arch. It is usually dived as an expedition-style boat trip, with dolphins common at the surface and shark encounters possible outside the arch on the right day.
Conservative baseline from public research. No community dives logged yet.
Depth range, seasonality, and planning context.
Reported Depth
15m - 30m
Depth Note
The inner arch area is described at about 15 m, with the outer shark area around 30 m.
Best Season
Summer to fall
Typical Conditions
Open-ocean expedition dive with long boat access, clear-water windows, and current that can be strong enough to shape the dive.
Hazards, restrictions, and access requirements.
Key Hazards
Safety Notes
Keep a tight group, watch current changes, and plan conservatively for the long crossing.
Access Restrictions
Only practical on a booked boat dive with an Ogasawara operator and a weather window that allows the crossing.
Legal Notes
Follow operator briefings and island-area rules; weather can change the plan quickly.
Community notes to help plan your visit.
Scuba Diving
The site is best for confident recreational divers who can keep close to the guide when current is running.
Freediving
Maguroana reads more like a scuba objective than a casual freedive site because the signature action sits around the arch and outer rocks.
Snorkeling
Snorkeling is mainly for surface dolphin watching rather than for working the arch itself.
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Directional shelter context for incoming swell.
Species commonly reported at this site, with direct links into their wildlife guides.
Community dive logs and visit reports for this site.
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Average conditions based on logged dives & visits.
Planning answers for access, conditions, timing, and site logistics.
Last Updated
Research Sources
Ogasawara operator page describing Tuna Cave (Maguro Ana) as a major dive point with large marine life.
Independent article describing the Maguroana arch, its dimensions, and the outer shark area.
Ogasawara village activity page describing Maguro Ana tuna and dolphin activity in the islands.
Official Ogasawara brochure noting Maguro Ana tuna concentrations in the summer and fall season.
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