Amami's Rivers

Characteristics of Rivers on Amami Oshima

The Yuwandake mountain standing at 694m (approx. 2277 feet) in height is the highest peak on Amami Oshima. It is connected with other glossy laurel forests forming a mountain range in the mid-central region of the island. Unlike other areas in Ryukyu Islands, a warm and humid climate brings an annual precipitation of nearly 3000mm (approx. 10 feet), creating a few rivers stretching over 10km (approx. 6 miles) in length.  Most of the river bases are covered with forests with well-developed mid-stream. Every time these rivers meander, they create numerous shallow and deep pools. As a result, extensive mangroves have been formed at river basins as in the Yakugachi River and Sumiyo River.

Yakugachi-gawa (Yakugachi River)

There are nearly 300 species of inland water fish that have been identified to exist on Amami Oshima.  Among them, very few of them spend their lifetime in freshwater areas and those are called “pure freshwater fish.”  One of such rare species is Minami Medaka (Japanese rice fish: Oryzias latipe).  In general, the fish most often spotted are migratory ones; in other words, those that traverse between rivers and the ocean (this phenomenon called diadromous migration). 

Giant mottled eel (Anguilla marmorata)

These include Oo unagi (giant mottled eel: Anguilla marmorata), Yugoi (flag tail: Kuhlia marginata), and a species of Yoshinobori (goby: Rhinogobius spp.).  Estuaries, as represented by mangroves, are ideal places to find fish as brackish water areas, where freshwater and saltwater come together, provides rich and diverse environments, as well as a wealth of benthos, which are feeds to fish. Species of Hiraaji (Horse kingfish: Caranx spp), juveniles of Fuedai species (starsnapper: Lutjanus spp.), Minami Mikuro dai (Okinawa seabream: Acanthopagrus sivicolus), bora species (gray mullet: Mugilidae spp.) and variety of species of haze (goby: Gobioidei spp.) also thrive in mangroves.

​​Rhinogobius yonezawai

Rhinogobius giurinus

Okinawa seabream (Acanthopagrus sivicolus)

Japanese mitten crab (Eriocheir japonica)

Photos:  Toshihiko Yonezawa, Horizon Editorial Office

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