THE NANPŌ ISLANDS
The islands of the Nanpō archipelago, stretching south off the Izu Peninsula, are all administered by the Tōkyō Metropolis, though some islands are thousands of miles away from the capital, far into the Philippine Sea.
The main diving areas are the Izu Islands and the Ogasawara/Bonin Islands, which offer generally warm water and increasingly subtropical conditions as you go further south.
The Nanpō islands offer great diving, in a unique environment, unlike what you would find elsewhere in Japan.
This is primarily due to the island chain’s geographical position, with stunning volcanic topography and many endemic species that developed there, in relative isolation (like Hachijō-jima and Ogasawara’s emblematic Yūzen/wrought-iron butterflyfish, Chaetodon daedalma).
NANPŌ ARCHIPELAGO
The Nanpō archipelago comprises the following groups of islands:
The Izu Islands (Izu-shotō)
There are more than a dozen Izu islands and islets, out of which nine are currently inhabited, including the historical 7 main islands, Izu Shichitō (伊豆七島, or Seven Islands of Izu):
- Izu Ōshima
- To-shima
- Nii-jima
- Kōzu-shima
- Miyake-jima
- Mikura-jima
- Hachijō-jima
The two other inhabited Izu islands are:
- Shikine-jima
- Aogashima
The Ogasawara / Bonin Islands
(Ogasawara Guntō)
which are 1000km+ south of Tōkyō
- Mukojima Rettō
- Chichijima Rettō
- Hahajima Rettō
The Volcano Islands (Kazan Rettō)
- Kita Iwo Jima (North Iwo Jima)
- Iwo Jima
- Minami Iwo Jima (South Iwo Jima)
- Nishinoshima
The Okinotorishima islet, located 1,740 km southwest of Tōkyō.
Minamitorishima island, also know as Marcus Island, located 1,848 km southeast of Tōkyō, with its own Exclusive Economic Zone
The Nanpō archipelago’s diving areas start, off the coast of the Izu Peninsula, with the 7 main Izu Islands, that offer great diving (and famous sites such as Nazumado, Akinohama, and Keikai).
The Izu islands are strongly affected by the Kuroshio warm current, and features strong seasonal changes in water temperatures and species.
Some of the Izu islands are close to the mainlaind, and easily reached from the Izu Peninsula.
Others are more remote, and reachable by ferry or plane from Tōkyō (Izu Ōshima and Hachijō-jima have airports).
The Nanpō archipelago’s other main diving areas is the Ogasawara/Bonin Islands, reachable only by a 26 hour+ ferry ride from Tōkyō (no airport…).
The Nanpō archipelago’s main inhabited islands have been given the name “Tokyo Eleven Islands” in recent tourism-oriented material.
The Ogasawara islands are sometimes nicknamed the “Galapagos of Japan/the Orient”.
While this might be pushing it a little, there is logic behind this nickname, in that these islands, like the Galapagos, were never connected to any continental landmass.
Which means that their animal, plant and marine life all evolved independently, resulting in a large number of endemic species.
Similarly, the remote Izu islands share many common features with the equally volcanic and isolated Macaronesian archipelago, is found off the coast of West Africa, in the Atlantic Ocean.
The archipelago is made up of the Azores, Madeira, Canary and Cape Verde Islands (mainly administered by Portugal and Spain), which are also great diving destinations, and affected by a warm current branching off the North Atlantic Current (Canary Current).
Izu islands, the “Azores of Japan”®, anyone? 😉
MAIN DIVING AREAS MENTIONED
- Izu Islands (Tōkyō Metropolis)
– Izu Ōshima
– Shikine-jima
– Kōzu-shima
– Miyake and Mikura-jima
– Hachijō-jima - Ogasawara/Bonin Islands (Tōkyō Metropolis)
– Chichi-jima
DIVING HIGHLIGHTS AND ICONIC MARINE LIFE
CORAL REEFS, BLUE WATER AND VISIBILITY
The islands of the Nanpō archipelago offer the chance to dive on healthy hard and soft coral reefs.
The waters of the Izu and Ogasawara islands are particularly famous for their blue colours (“Hachijō Blue”, “Bonin Blue”) and great seasonal visibility.
WRECK DIVING
The Chichi-jima area in the Ogasawara/Bonin Islands has numerous WWII wrecks, including the Daibi-Maru (sometimes recorded as Daimi-Maru), lying at 33 m depth in Chichi-jima harbour.
These wrecks are not all easily accessible, and some require special equipment and adequate training, and authorisations, so do your research.
Some beautiful pictures of the wreacks of the Ogasawara islands area can be found here.
ICONIC SPECIES
The islands of the Nanpō archipelago are famous for their endemism, where species developped in relative isolation.
There many local endemic/iconic species, including schools of wrought-iron butterflyfish (Chaetodon daedalma) and red tail triggerfish (Xanthichthys mento) found in the Nanpō archipelago’s Izu and Ogasawara islands.
Sand tiger sharks / ragged-tooth sand sharks “raggies” (Carcharias taurus) are found all year round in the Ogasawara Islands.
MACRO DIVING, ODD AND RARE CRITTERS
The Nanpō Islands offers great macro diving opportunities, where you dive to spot/photograph/film small rare critters.
The Nanpō Archipelago’s Izu Islands, especially Izu Ōshima, Hachijō-jima and Kōzu-shima, are famous in Japan for their rich macro-life, rare nudibranchs and all the usual suspects but also the famous Japanese pigmy seahorse (Hippocampus japapigu), along with more classic pigmy seahorses (Hippocampus bargibanti,. h. colemani and h. pontohi), often spotted on the Izu and also in the Ogasawara Islands.
Other macro highlights include:
Various pipefish, including ornate and robust ghost pipefish (Solenostomus paradoxus and S. cyanopterus)
Crabs, including spider crabs, decorator crabs
Rare and odd-looking frogfish/anglerfish (Antennariidae), especially in Ishibashi or Hayama (Kanagawa Pref.)
Shrimps, including the highly photogenic harlequin shrimp (Hymenocera picta) and imperial shrimp (Periclemenes imperator) or skeleton shrimps.
Rhinopias, leaf scorpion fish (Taenianotus triacanthus), seamoths (Pegasidae), devilfish (Inimicus) and other weird, photogenic critters
Rare blennies and gobies
Rare, singular jellyfish and anemones
SCHOOLING HAMMERHEAD SHARKS
It is possible see schools of scalloped hammerhead sharks (Sphyrna lewini) in the Izu islands.
While this is definitely less famous, and more adventurous Japan’s famous hammerhead viewing sites of Izu’s Mikomoto islets or Okinawa’s Yonaguni island, Izu Ōshima Island is only a 2-hour fast-ferry ride or a 40 min flight away from Tōkyō.
In the summer months, lucky divers can observe schools of scalloped hammerhead (Sphyrna lewini) on a very early morning beach entry dive (!!!) at Keikai, which is quite a unique experience.
You do have to get up at 4 am, and it is an advanced dive, quite shallow but with strong current, where you hold on to rock and watch the action go by.
On a good day, you might get to see what people call the “hammer river”, a long stream of hammerheads flowing by in the current…
Best period to view the hammerheads is said to be between mid-June and October.
DOLPHINS
Swimming and freediving/snorkeling with pods of wild bottlenose dolphins (Tursiop aduncus) is one of the highlights of the Nanpō islands, both in the Izu and Ogasawara island groups.
In the Izu island, the hub is Miyake-jima, from which a one-hour boat trip takes you Mikura-jima, where it is possible to join the 3 or 4 boat trips per day organised to snorkel/freedive with the island’s resident pods of 200+ wild (non-captive) bottlenose dolphins, who often come up to swimmers and snorkelers and play around them.
The Miyake branch of the Dolphin Communication Project tracks the pods of dolphins that live around the island.
Dolphins are sometimes also seen on dive sites of other Izu islands.
The Ogasawara/Bonin Islands also offer many great opportunities freedive /snorkel with wild dolphins and other cetaceans, and they are very frequently spotted by scuba divers on local dive sites.
TURTLES
Shikine-jima, Hachijō-jima and the other Izu islands are all famous for their “sea” turtle populations, including green and hawksbill turtles (Chelonia mydas and Eretmochelys imbricata)
Shikine-jima also has a spot where turtles like to relax in warmth of the hot springs that flow into the sea, a kind of reptilian alternative to Nagano’s bathing “snow monkey”, if you wish…
From February to August the Ogasawara/Bonin Islands are said to become one of the biggest nesting ground of green turtles in Japan.
WHALES
Humpback whales (Megaptera novaeangliae) are spotted, mostly from the boat or shore but quite regularly underwater in the winter to spring months, in the Ogasawara/Bonin Islands (usually between February and April), and also around the Izu Islands in the winter months (December to March).
Keep in mind that unless you encounter a whale while already in the water, interaction with the whales is not allowed in the Ogasawara islands, as boats are required to respect a 100 m exclusion zone around humpback whales.
Sperm whales (Physeter macrocephalus) are also common in the Ogasawara islands during the summer to autumn months, and the islands are one of Japan’s best whale watching / spotting destinations along with the north of the Okinawa island chain.
A 50 m exclusion zone is to be respected around sperm whales, again, unless you are already in the water and the whale comes up to you.
Seasonal whale watching in the Izu islands (such as Hachijō, where whales can sometimes be seen from some of the island’s outdoor hot springs / rotenburo) is still developing as an activity, so expect to hear more on that in the future.
SCHOOLING FISH, PELAGICS AND PREDATORS
Large schools migratory fish and pelagics, including dogtooth tuna (Gymnosarda unicolor), bluefin trevally (Caranx melampygus), big-eye trevallies great amberjacks (Seriola dumerili) Japanese amberjack (Seriola quinqueradiata) and rainbow runners (Elagatis bipinnulata) and various types of larger pelagic sharks can be seen seasonally in the Nanpō Islands.
This is especially true in the more remote islands of the Nanpō archipelago, from Hachijō-jima in the Izu Islands to the Ogasawara Islands.
The Ogasawara islands are famous for their massive schools of dogtooth tuna (Gymnosarda unicolor), Japanese Spanish mackerel (Scomberomorus niphonius) greater amberjacks (Seriola dumerili), trevallies or barracudas.
Pelagic thresher sharks (Alopias pelagicus), whale sharks (Rhincodon typus) and scalloped hammerhead sharks are sometimes spotted at different sites in the Nanpō islands, due to the combined effects of currents, relative isolation and deep water.
Smaller sharks such as sleeping white-tip reef sharks (Triaenodon obesus) in winter months at Kamogawa (Chiba Pref.), various rays including guitar-sharks/shovelnose rays (Glaucostegus typus) or Japanese bullhead sharks (Heterodontus japonicus) are spotted in most of the area, including the Izu Islands.
Schools of Japanese eagle rays (Myliobatis tobijei) can sometimes be seen in the summer months at Nishikawana (Chiba Pref)
Though rare, manta rays, mostly giant “oceanic” manta rays (Mobula birostris) are regularly spotted in the Ogasawara islands area (see here for more info on the subject)
SPAWNING EVENTS AND AGGREGATIONS
Japanese flying squid (Todarodes pacificus) spawning events can be observed in May in Miyake-jima in the Izu Islands,, as squid brought by the Kuroshio current congregate and spawn in the area.
The squids deposit long white tubes full of eggs in clusters on tree branches placed there by dive operators, at about 14-16m depth, on shore dive from Okubohama beach.
OTHER
It’s possible to dive at an underwater hot-spring at Shikine island (Izu Islands, 3-hour boat ride from Tōkyō), which is also sometimes visited by turtles.
Click here for more precise, detailed and practical information on diving in the Kantō region