Boundaries

The ecoregion includes all but the northwest coast of Sakhalin Island (excluding the Amurskiy Liman Strait basin and the southern coast of Sakhalinskiy Bay), Hokkaido Island, and the southern Kuril Islands (from north to south: Ostrova Chernyye Brat’ya, Urup, Iturup, Kunashir, Shikotan, Zelenyy, and Habomai islands).

The continental part of the ecoregion encompasses coastal rivers of the Sea of Japan from south of the Amurskiy Liman Strait (Zaliv Chikhacheva Bay) down to the Tumen-Ula [Tumannaya = Tuman-gang] (Lake Khasan inclusive). The western border of the ecoregion (with Lower Amur [616]) runs along the dividing ranges of the Sikhote-Alin’ Mountains (from north to south): Sredinnyy Khrebet, Golyye Gory, and Bolshoy Yang. The southwestern border follows the Khrebet Przhevalskogo Range and the northwestern slopes of the Nangang Mountains.

Topography

The Sikhote-Alin Mountains stretch along the continental portion of the ecoregion, with elevations reaching over 2000 m.

The Kuril Islands extend from Cape Lopatka (50° 56’ N and 156° 30’ E) of the Kamchatka Peninsula down to Hokkaido Island (40° 25’ N and 145° 24’ E), dividing the Sea of Okhotsk from the Pacific Ocean. The total length of the island chain is around 1200 km. There is an additional chain of small islands (the Lesser Kuril Ridge) 100 km long along the southern coast of Kunashir Island. There are over 30 islands, but only 10 of them are larger than 200 km². There are also a number of rocks.

Sakhalin lies off the East Asian coast between 54° 24’ N (Cape Elizabeth) and 45° 54’ N (Cape Krilion) for a distance of 948 km. The maximum width of Sakhalin reaches 157 km, and the minimum width in the narrowest part of the Schmidt Peninsula is 6 km. The average width of the island is approximately 100 km, and its area is 76 400 km². The northwestern part of the island nearly adjoins the continent, and is only separated from it by the shallow Nevelsky Strait, with depths of 7-12 m. The southern part of Sakhalin is separated from Hokkaido by only 40 km at the La Pérouse Strait, its average depth being approximately 60-70 m.

Much of the relief of Sakhalin is relatively diverse and complex. In the southern and central part of the island mountains of average altitude (500-800 m) are predominant, and only a few peaks exceed 1000 m. The Eastern Sakhalin Mountains, stretching from the Terpeniya Peninsula in the south up to the Nabil River in the north, are a major mountain chain in Sakhalin.

The Kuril Islands are located within a tectonic and volcanic zone that is characterized by a combination of young active volcanoes and adjacent deep oceanic hollows. The surface structure of the Kuril Islands is largely determined by ancient and recent volcanic activity connected with tectonic breaks. About 160 volcanoes can be counted today, 40 of which are currently active. Often lakes are located in craters of volcanoes.

Bussol Strait (over 2000 m deep), lying between Urup and Simushir islands in the central Kurils, is the most significant biogeographic boundary within the Archipelagho, and divides the Archipelago into two parts, the northern one, which belongs to the Kamchatka & Northern Kurils ecoregion [613], and the southern one, which belong to this ecoregion.

The largest southern Kuril Islands (from north to south) are Urup, Iturup, Kunashir, and Shikotan. The islands are separated from eachother by shallow straights. Most islands contain one to several lakes, which are connected by a stream to the sea or are isolated.

Tectonic structures formed the relief of the islands. Thus, the Eastern Sakhalin composite anticline includes the Easterm Sakhalin Mountains, which stretch from the Schmidt Peninsula up to the Tonino-Aniva Peninsula on Sakhalin Island. The Western Sakhalin composite anicline conforms to the Western Sakhalin Mountains. The Central Sakhalin synclinorium forms a system of intermontane depressions that stretch in a sublongitudinal direction. These tectonic depressions are Baikalskaya, Tym’-Poronaiskaya, and Susunaiskaya. They continue further south on Hokkaido Island, which together with Sakhalin represents a single elevation of the Cenozoic folded system.

Freshwater habitats

The rivers of the ecoregion are characterized by a relatively low spring tide, heavy summer floods, and particularly low winter mean water. The regime of Sakhalin\'s rivers is complex, reflecting three stages of flood. Spring flood is caused by snowmelt within the plain parts of drainages; in early summer, the flood is formed by mountain snowmelt; and, eventually, middle summer (July – August) floods are caused by monsoon rains.

Many of the ecoregion’s rivers are of mountain character in the upper reaches and of plain character in the lower reaches. The rivers normally freeze in November – December and break up in April or May.

Water bodies of Sakhalin are diverse, comprising more than 16 000 lakes of various types, including water erosion (bayous), water-accumulative (delta and lagoon), dammed, holed (thermokarst), anthropogenic (reservoirs), and volcanic, with a total surface area of 1004 km². The overwhelming majority of the lakes have surface areas less than 0.4 km² and are associated with low and plain regions. A number of large lakes are of marine origin. They were formed by surf waves that inwashed sand beaches (dunes), separating the bays from the sea. The largest of these lakes are Nevskoye, Tonnai, Ainskoye, Vavaiskoye, and Sladkoye. In the North-Sakhalin Lowland, on the coast are large lagoons, small bays, Lunskii, Nabilskii, Nyiskii, Chaivo, and Piltun, which are separated from the sea by sand-pebble spits, sometimes attaining considerable width. There are thermokarst lakes in the northern part of the island, and bayous in its middle part, particularly in floodplains of the Tym (280 km) and Poronai (250 km) rivers.

South of the Amur River estuary up to the frontier with Korea many relatively small rivers, flowing from the eastern slopes of the Sikhote-Alin, fall into the Sea of Japan. They all have a mountain character of flow, large slopes, and high flow velocities. The largerst of these rivers is the Tumnin River, which is 270 km in length and 22 400 km² in drainage area. Catchment areas of other rivers of this group do not exceed 6000-7000 km².

In the region of Vladivostok, the Suchan, Maikhe, and Suifun [Razdol’naya] rivers fall into the Peter the Great Bay. The largest of these is the Suifun River, with a length of 288 km and drainage area of 18 450 km². The Tumannaya River flows along the frontiers of Russia, China, and Korea. It begins on the eastern slopes of the extinct Pektusan Volcano on the Chanbaishan Plateau. The length of the river is 516 km, and catchment area is 33 168 km². Due to large fluctuations in atmospheric precipitation, the major part of which falls from July through August, and shallowness of rivers in winter, the flow throughout the year changes ten-fold. A large part of the Tumannaya River drainage is situated in highlands, which accounts for its high flow velocity. The main tributaries of the Tumannaya River are the Gaiya, Buerkhaton, Khailan, and Khunchun (left tributaries) rivers. A large part of the catchment area of the Tumannaya River lies at an altitude of 400-1000 m in the uplands, covered by forest and shrubs with narrow valleys. Approximately 40-50 km from the estuary the lower Tumannaya River has a plain character. This area includes extensive floodplains and marshlands abounding in lakes and lagoons. The river width varies from 200 m around 20 km upstream from the estuary, up to 1500 m within the esuary.

Water bodies of the Kurils represent a wide variety of relatively small streams and lakes that are connected to the sea. Some of them are influenced by volcanic activity.

Terrestrial habitats

The terrestrial ecoregions include Okhotsk-Manchurian taiga (north) and Ussuri broadleaf and mixed forests (south) along the Maritime coast; Sakalin Island taiga (north) and South Sakhalin-Kurile mixed forests (southwest) on Sakhalin Island; Hokkaido montane conifer forests and Hokkaido deciduous forests on Hokkaido Island; and South Sakhalin-Kurile mixed forests and Kamchatcka-Kurile meadows and sparse forests on the south Kuril Islands.

Description of endemic fishes

There are eight endemic species in the ecoregion, including two Gymnogobius (G. petschiliensis and G. taranetzi) and two Cottus (C. czerskii and C. volki) species. Others include forktongue goby (Chaenogobius annularis), Gobio macrocephalus, Pungitius polyakovi, and seaweed pipefish (Syngnathus acusimilis). A large portion of the endemic forms are from the Cottidae and Gobiidae families, which are secondary freshwater or euryhaline. The systematics of many of them need further studies.

Other noteworthy fishes

Acipenser medyrostris mikadoiis is an extremely rare and threatened fish. It is still known to enter a few rivers along the Sea of Japan coast for spawning.

Charrs of the Kuril Islands represent an interesting complex of brook, riverine, lacustrine, and migratory forms.

An undescribed species, Kunashir smelt (Hypomesus chishimaensis) (Kunashir Island) may be a distinct species from the southernmost islands of the Kuril Islands. It may represent a local lacustrine resident form of Japanese smelt (Hypomesus nipponensis).

Ecological phenomena

The distribution of species in rivers of the ecoregion is mosaic, correlated with the size of the river drainage. In shallow rivers the number of fish species is lower than in large rivers. Primary freshwater fishes are absent in the Kuril Islands.

Justification for delineation

As early as 1889 A.M. Nikolskiy concluded that in the Pleistocene Sakhalin and Hokkaido islands on the one hand, and the Japanese islands (Honshu and islands south of it) and Korea on the otherhand, were two peninsulas of the Asian continent separated by the sea at the present Tsugaru Strait. An analogous correlation of land and sea could have existed in the Late Miocene, Late Pliocene through the Early Eopleistocene, and in the cold epochs of the second half of the Pleistocene (Pletnev 2004). During the “cold” Pleistocene (0.7-0.01 mya) repeated climatic changes (thermo- and cryochrones) and wide-range fluctuations of the sea level, from -130 m to 10-15 m, were noted.

During the cryochrones (60 000 - 40 000 and 22 000 - 11 000 years ago) glacioeustatic a sea level decline of 100—130 m occurred, which led to the closing of the shallow Nevelsky and La Pérouse straits and the origination of isthmuses in their place. The last post-glacial transgression, which began 15 000 - 17 000 years ago, developed rapidly, with an initial rise in sea level up to 9 m per 1000 years. As a result, in less than 10 000 years the sea level reached present levels or even slightly higher levels, after which the rate of the transgression slowed down abruptly. The La Pérouse Strait and Nevelsky Strait opened, 12 000 - 11 000 years ago and ca 7000 years ago respectively, and Sakhalin became an island again.

The wide-ranging changes of sea level in the “cold” Pleistocene repeatedly led to the joining of Sakhalin with the continent and Hokkaido Island. The most favorable conditions for penetration of thermophilous elements into Sakhalin occurred in the Eopleistocene. For the dispersal of cryophilous elements of the biota, cold epochs of the Late Pleistocene were preferable, when sea level declined to 110 - 130 m and mean annual temperature was 7~9 °C lower than present.

There are objective historic prerequisites for joining all of the subregions in question into one ecoregion. It includes a relatively large number of species with a predominance of originally marine (mostly migratory) and euryhaline forms. The number of residential, originally freshwater, forms are much fewer than in large river drainage systems of Amur or Siberia. The diversity of freshwater, amphidromous, or euryhaline gobiids is characteristic of the ecoregion.

Level of taxonomic exploration

Good