The Sea of Japan (日本海)

The Sea of Japan is a marginal sea of the Western Pacific being surrounded by Sakhalin, Hokkaido, Honshu (the main island of Japan), Kyushu as well as the Democratic People's Republic of Korea (North Korea), the Republic of Korea and the Russian Federation in the Eurasian Continent.

In English, it is referred to as the Sea of Japan or Japan Sea. It is referred to as mer du Japon, Japanisches Meer, Японское море and일본해 in French, German, Russian and Korean, respectively.

In South Korea it is also referred to as 동해 (Donghae or East Sea) while in North Korea it is known as 조선동해(Joseon Donghae or Korea East Sea) or 조선해 (Joseonghae or Korea Sea) and some Korean people call it 동조선해 (Don Joseaonghae or East Korea Sea). Nevertheless, the United Nations and the majority of international marine charts currently refer it to as the 'Sea of Japan' and those Korean names are not common worldwide. Both South and North Korea insist that 'Sea of Japan' be replaced by or followed by 'East Sea' because the current naming is a reminder of colonial administration by Japan. For details of this naming issue, see Sea of Japan Naming Dispute.


Its average depth is 1,752 meters, the greatest depth is 3,742 meters and the surface area is 978,000 square meters. Surrounding the Yamato Bank (approximately 400 meters in water depth), there are 3 major deep basins: the Japan Basin (approximately 3,000 meters in water depth) on the north, the Yamato Basin on the southwest and the Tsushima Basin on the southeast (approximately 2,500 meters in water depth, respectively). Off the coast of the Toyama Bay, the Toyama Deep-Sea Channel with as deep as 1,000 meters in water depth stretches approximately 500 kilometers in length. There are continental shelves that extend along the eastern coastal line while on the west side, they are very narrow particularly along the coast of the Korean Peninsula with approximately 30 kilometer in width.

The Sea of Japan is connected to the Okhotsk Sea through the Mamiya Strait (the Tatar Strait) between the continent and Sakhalin as well as through the Soya Strait between Sakhalin and Hokkaido. The Sea of Japan is also connected to the Pacific Ocean through the Tsugaru Strait between Hokkaido and Honshu while it is connected to the East China Sea through the Eastern Channel of the Tsushima Strait between Kyushu and Tsushima Island as well as through the Korea Strait between Tsushima Island and South Korea.

Since the straits have shallow water depth, there is little exchange of sea water with open seas except for the Tsushima Current from the Tsushima Strait flowing in. Influxes of warm currents have influence of the temperate climate of Japan. There is the Liman Cold Current flowing on the north but, as a result of a geological survey, it has come to light that the the Oyashio current (the Kuril current) was once running in that area.

In the deep layer, there is the cold and dissolved oxygen-rich sea water called the Proper Water in the Japan Sea which has totally different properties from that of the Pacific Ocean.

The areas on the north and southwest are rich with marine resources and it is considered economically important because minerals, natural gas as well as small amount of petroleum and methane hydrate are also available.

Up to 40 million years ago, the Japanese archipelago was part of the Asian Continent but it became detached from the continent approximately between 40 million and 20 million years ago. Because of this, the original form of the Sea of Japan was created and after expanding, it was arranged into approximately the current layout several million years ago. The Tsushima Strait was still part of the Eurasian Continent then and it is said that the strait was formed during Quaternary period. Later on, due to the current sea level rise that occurred worldwide during the glacial period, the strait having shallow water depth of approximately 130 meters kept opening and closing. As a result, sediment lithofacies, isotopic composition ratios and element concentrations have gone through dramatic changes.

Between Sakhalin and the coastline of the Japanese archipelago, there is a band of areas where the magnitude 7 class earthquakes frequently occur that is referred to as the Japan Sea Eastern Margin Mobile Belt. There were various earthquakes in the Japan Sea Eastern Margin Mobile Belt so far including the Neftegorsk earthquake, the South-West off Hokkaido earthquake, Middle Japan Sea earthquake, Shonai earthquake, Niigata earthquake, Niigata Chuetsu earthquake and the Niigataken Chuetsu-oki Earthquake in 2007.

Marine Pollution

With regard to wreckage, many kinds of waste materials which have been illegally disposed of mainly by Korean and Chinese freight ships and fishing boats sailing the Sea of Japan as well as from the Korean Peninsula and Japanese mainland moves with the sea current and drifts ashore along the coast of Tsushima and the Sea of Japan. The volume of wreckage is so massive that it places an enormous financial burden on the municipalities in coastal regions. Additionally, there is the possibility that radioactive materials abandoned by some countries including Russia have polluted deep waters whereby there is a concern about contamination of crabs and deep-sea fish. Russia in the midst of economic deterioration in those days was discarding nuclear power reactors of the old nuclear submarines of the Pacific fleet (Russian Navy) in the ocean trench over international waters of the Sea of Japan which is considered to be particularly problematic. Additionally, due to bad weather in the winter months, there have been many marine accidents including the Nakhodka oil spill accident which polluted the coastline with a large amount of crude oil. There is no end of dumping waste oil in the ocean by some of the Chinese, Russian and Korean ships after cleaning inside those ships with seawater. Mostly between winter and spring, there have been some accidents posing a risk to navigation in which large quantities of lumber or the like were spilled from ships underway.

Isoyake (shore-burning)

When vegetations are wiped out in the rocky areas along the shore, a wide area of rocky shore will look ash white as roasted turban shell and, hence, this term 'isoyake' which means 'shore-burning.'

It is a phenomenon seen in all of the Sea of Japan coastal areas which causes a concern over a serious impact on the entire fishing industry, with problems including that the fish population is drastically reduced and that, due to the decreased food, the growth of juvenile fish of those species valuable to human that are spawned and grow in the coastal areas will be challenged.

Due to the fact that shore-burning is uncommon around the immediate areas where river waters flow in, it is considered to be caused by change in seawater.

According to the widely-accepted opinions over the change in seawater, it results from the marine pollution caused by endocrine disrupters contained in ship bottom paint or the reduced organic matter due to the flood control measures installed for inflowing rivers. As one of the latest opinion, the reduced organic matters in seawater due to global warming (oligotrophication and reduced nutrients) is pointed out, but the cause remains unknown.

Although 'shore-burning' is the normal condition for those who are used to seeing the present rocky shores and they can not get a real sense of that term, half a century ago, people commonly saw rocky shores under water which were so densely covered with marine plants that rocks were not visible.

Eco-System and Fishing Industry

Due to the fact that there are smaller numbers of breeds and fewer indigenous species comparing to that found in the Pacific Ocean, it is said that the formation of the Sea of Japan occurred not too long ago. There are generally an abundance of costal-zone bottom animals such as crabs and slight difference is noted in fish fauna from one side of the Noto Peninsula to another. Comparing to the Pacific Ocean, the northern most range for southern species extends far north due to the effect of warm current of the Tsushima Strait. For instance, turban shells are harvested even in Aomori Prefecture on the side of the Sea of Japan, whereas, they are not found in areas north of the Kanto region on the side of the Pacific Ocean.

There are an abundance of plankton in areas where water is cold and on continental shelf off the coast, whereas, very small amount in the central region. The type of plankton is broken down into warm water species in the Tushima Warm Current and cold water species in the Liman Cold Current, but the distribution of both types is not as clearly divided as water mass distribution and there is a wide sea area where they coexist. The northern hemisphere fish include herring, salmon, trout and cod, whereas, among the southern hemisphere fish, there are a large number of yellow tails that somewhat belongs to the temperate zone fish variety but the representative warm water fish such as bonito and tuna are hardly ever caught. Those living in the temperate zone such as red sea bream, true sardines, mackerel and flatfish are more important as fish.
Comparing the distribution of these fish species to that for the Pacific Ocean, there are the following characteristics:

The recurrent migration range of the southern hemisphere fish includes the north of the Pacific Ocean coastline, whereas, the boundary for the northern hemisphere fish is far down south of that point.

Due to the fact that there are not many bonito or tuna, deep-sea fishing except for mackerel longline fishing in the central area of the Sea of Japan has not developed.

Surface water becomes warm in the summer but lower layer water just below the surface remains cold whereby warm water fish such as sardine, mackerel and sea bream is caught in the area close to the surface while cold water fish such as cutlass fish and cod is caught in deep waters and on ocean floor.

It has been also known as the migratory route of whales since ancient times and numerous whale fishing villages used to be found along the coast. As the number of whales has been sharply decreased due to whaling, whale sightings are very rare these days but many delphinoid species and, among baleen whale species, small population of minke whales and fin whales that do not take on extensive migrations remain in existence today.


The magical views created by the sea and sands such as Amanohashidate, Tottori-sakyu Sand Dunes, Senrigahama Beach and Tango no Nakisuna are well known. Additionally, numerous scenic spots and national monuments scatter in areas along the Sea of Japan and the coastlines from Hokkaido to Tsushima offer valuable tourist attractions.

National Parks

The coastal areas of the Sea of Japan that have been designated as the national parks include the following three: the Rishiri-Rebun-Sarobetsu National Park, Sanin-Kaigan National Park and Daisen-Oki National Park.

Quasi-National Parks

There are numerous areas along the Sea of Japan coastline that have been designated as quasi-national parks including the Shokanbetsu-Teuri-Yagishiri Quasi-National Park, Niseko-Shakotan-Otaru Kaigan Quasi-National Park, Tsugaru Quasi-National Park, Oga Quasi-National Park, Chokai Quasi-National Park, Sado-Yahiko-Yoneyana Quasi-National Park, Noto Peninsula Quasi-National Park, Echizen Kaga Coast Quasi-National Park, Wakasa Bay Quasi-National Park, Kitanagato Beach Quasi-National Park, Genkai Quasi-National Park and Iki-Tsushima Quasi-National Park but recently, constructions of roads, ports and harbors are damaging those landscapes.

Sea Route

There are numerous ferry routes in the Sea of Japan.

Higashi Nihon Ferry Co., Ltd. (sailing between Muroran and Hakata with a stop at Naoetsu in between) * Operation is currently suspended

Shin Nihonkai Ferry Co., Ltd. (sailing between Maizuru and Otaru; Tsuruga and Tomakomai with stops at Niigata and Akita in between [direct service is also available]; Niigata and Otaru)

Heart Land Ferry (sailing between Wakkanai and Odomari [Korsakov])

Kampu Ferry Co., Ltd.(sailing between Shimonoseki and Busan, South Korea)

Jet Ferry 'Beetle (Jet Ferry)' (sailing between Fukuoka and Busan, South Korea)

Orient Ferry Ltd. (sailing between Shimonoseki and Tsingtao, China)

Orient Ferry Ltd. (sailing between Shimonoseki and Taicang, China)

Additionally, during the summer, the sea routes between Shanghai City and North America usually start in the Sea of Japan proceeding to the Pacific Ocean via the Tsugaru Strait.

Territorial Dispute

There is a territorial dispute between Japan and South Korea over Takeshima Island (Shimane Prefecture) (Korean name is Dokdo Island), located in southwest under the occupation of the Republic of Korea.

Company names beginning with 'Nihonkai'

Nihonkai Shinpan Co., Ltd.

Shinnihonkai Shinbunsha (is a newspaper company in Tottori Prefecture publishing the Nihonkai Shimbun).
(The Press Osaka, the publisher of the Osaka Nichinichi Shimbun, is an affiliate of this company.)

Nihonkai Cable Network Co., Ltd. (a cable television broadcasting company)

Nihonkai Telecasting Co., Ltd. (abbreviated to NKT is an affiliate television station of Nippon Television Network Corporation providing broadcasting service in Tottori Prefecture and Shimane Prefecture)

Nihonkaimiso Co., Ltd. (is a manufacturer of miso or fermented soybean paste and soy sauce based at Toyama Prefecture and is famous for its commercial song written by Taro KIDA)

Nihonkai Gas Co., Ltd. (is a city gas and liquefied petroleum gas supplier mainly servicing Toyama Prefecture)

Shin Nihonkai Ferry Co., Ltd. (is a ferry operator based in Osaka City that sails between Maizuru Port and Akita Port with stops at Tsuruga Port and Niigata Port in between; between Otaru Port and Tomakomai East Port.

[Original Japanese]