The island of Shikoku has two major coastlines, one facing the Seto Inland Sea and its various straits, and the other the Pacific Ocean.
Thanks to the Kuroshio current, water temperatures stay warm even through the winter months, and diving is possible all year round.
The waters offer a great diversity of species, including subtropical and more temperate water marine life and particularly good macro diving, as well as reef diving on colonies of table and stony coral and remarkable pelagic action on more remote, exposed sites of the Pacific coast.
The Seto Inland Sea coast is dotted with small islands, and the underwater topography is varied, with drop-offs, pinnacles, arches and caves.
MAIN DIVING AREAS MENTIONED
Seto Inland Sea Coast
- Akehama (Ehime Prefecture)
- Ainan (Ehime Prefecture)
- Uguru (Ugu) Island (Kōchi Prefecture)
- Kashiwa Island (Kōchi Prefecture)
- Okitsu (Kōchi Prefecture)
- Muroto (Kōchi Prefecture)
- Kan-no-ura (Kōchi Prefecture)
- Takutsushi (Kōchi Prefecture)
- Mugi (Tokushima Prefecture)
- Shishikuisho (Tokushima Prefecture)
DIVING HIGHLIGHTS AND ICONIC MARINE LIFE
UNDERWATER VISIBILITY, HARD AND SOFT CORAL
Uguru (Ugu) Island, located 23 kilometers off the town of Sukumo, or Kashiwa Island on the coast of south-western Shikoku offer amazing underwater visibility in season, which is said to be up to 50m on a good day, probably the best salt-water visibility in the country.
The islands are also famous for their coral colonies, which are actively protected by the local government.
Sites like Tokushima Prefecture’s Mugi or Shishikuisho are famous for their colonies of hard and soft coral, including the Mugi’s “One Thousand Years Old Coral” (Porites lutea ), an impressive colony which now reaches a height of over 9 metres.
MACRO DIVING, ODD AND RARE CRITTERS
The Shikoku island region also offers good macro diving options, with over 100 types of nudibranchs recorded in the area, as well as various juveniles, frogfish, rare gobies or seahorses, especially on sites like Akehama (Ehime Pref.), Uguru and Kashiwa islands (Kōchi Pref.).
The small island of Kashiwa (Kōchi Pref.) is itself famous for its biodiversity, macro life and coral reefs, and has over 10 dive operators on its 4 km², catering mostly to macro diving enthusiasts and underwater photographers.
SCHOOLING FISH, PELAGICS AND PREDATORS
In the summer to autumn months, Pacific coast dive sites of the Kōchi prefecture offer the chance to see migratory fish such as rainbow runners (Elagatis bipinnulata), especially in Tatsukushi, or Japanese amberjacks (Seriola quinqueradiata) that congregate in large schools.
The more remote Uguru Island area, or more exposed Pacific coast sites of Okitsu and Muroto (Kōchi Pref.) all offer good chances of seeing turtles and also large migratory fish in season, including bluefin, dogtooth and yellowfin tuna, various mackerels, yellowtail and bigeye trevallies.
Other visitors include the occasional manta ray, mola-molas or hammerhead sharks.
Thresher sharks (Alopias vulpinus) are often seen in Tokushima Prefecture’s Mugi area, in the early summer months.
The famous Asian sheepshead wrasse (Semicossyphus reticulatus), can be observed on various Shikoku sites on the Seto Inland Sea.
Recently, a seasonal hammerhead shark viewing point was discovered in south-west Shikoku’s Ainan area (Ehime Prefecture)
Local high season for scalloped hammerheads (Sphyrna lewini) is said to be between July and September, and other than the hammerheads, oceanic black tip sharks (Carcharhinus limbatus) and blacktail reef sharks (Carcharhinus melanopterus) were also spotted.
Some photos of sightings can be seen here.
SPAWNING EVENTS AND AGGREGATIONS
Akehama (Ehime Prefecture) and Kashiwa-jima (Kōchi Pref.) also offer the chance to observe large schools of migratory fish as well as bigfin reef squid (Sepioteuthis lessoniana) spawning events in the summer months.
Kan-no-ura, on Kōchi Prefecture’s Pacific coast, offers divers one of Japan’s only chance to witness whitespotted bambooshark (Chiloscyllium plagiosum) spawning events between the months of May and July.
Loggerhead turtle (Caretta caretta) nesting events take place in Tokushima Prefecture’s Mugi area, from the end of June to July.
WHALES AND OTHER CETACEANS
Migratory whales are also seen in south Shikoku.
On Kōchi Prefecture’s Pacific coast, especially in the Kuroshio-chō area, the season runs from April to September, with the peak from July through September.
Common encounters include humpback whales (Megaptera novaeangliae), sperm whales (Physeter macrocephalus) and also Bryde’s whales (Balaenoptera brydei) Risso’s dolphins (Grampus griseus) or bottlenose dolphins (Tursiops aduncus)
Click here for more precise, detailed and practical information on diving in the Shikoku region.