Large aggregations of bigfin reef squid (Sepioteuthis lessoniana), an iconic Kuroshio/Tsushima current species, are often observed between the months of June and October in the Oga Peninsula (Akita Pref.) and around Sado Island (Niigata Pref.).
Bigfin reef squid (Sepioteuthis lessoniana) spawning events can be observed in May on Miyake-jima in the Izu Islands, as the 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.
This is also observed on other islands in the area.
Bigfin reef squid (Sepioteuthis lessoniana) spawning events can be observed seasonally, especially in the Futo dive site area, on the east coast of the Izu Penisula, between June to August.
On the Sea of Japan side, Toyama Prefecture’s Namerikawa area is famous for its aggregations of bioluminescent firefly squid (Watasenia scintillans) which come to lay eggs in shallower waters, and scintillate like underwater fireflies…
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.
The are many seasonal squid spawning events around Kyūshū, including bigfin reef squid (Sepioteuthis lessoniana) in the spring months, especially on Miyazaki Prefecture dive sites.
Another interesting phenomenon is the “underwater aurora borealis”, formed by a large mass of bioluminescent algae. This rather unique underwater phenomenon, visible near Iōjima in Kyūshū’s Satsunan islands, (Kagoshima Pref.), is best viewed in autumn, when the visibility is good and a powerful Kuroshio warm current brings the right nutrients and conditions
Broadclub cuttlefish (Sepia latimanus) are commonly spotted on all reefs of the Okinawa region, but they’re especially common between winter and spring on Ishigaki island where, in early March, impressive mating then spawning events take place on the west coast of the island.
Iriomote island is famous for its coral spawning events, that very lucky divers can observe on night dives from May to September, roughly a few day after the full moon.