Kushiro Marsh

The Kushiro Plain is a low-lying, marshy peatland less than 10 meters above sea level that covers about 80% of the Kushiro Plain, which spreads across the lower reaches of the Kushiro and Akan Rivers in eastern Hokkaido. It spans Kushiro City and the towns of Kushiro, Shibecha, and Tsurui, all under the jurisdiction of the Kushiro Regional Development Bureau. Countless small and medium-sized rivers flow into the area from the surrounding plateaus and hills, creating a palm-shaped marshland, and remnants of marine life such as Shirarutoro Numa, Lake Toro, and Lake Takkobu Numa line the Kushiro River that flows to the east, which is thought to have once been a deep bay. The area is home to a valuable low-lying marsh ecosystem, with approximately 170 species of birds, including the Japanese crane, a special natural monument, the white-tailed sea eagle, a natural monument, and the Siberian spotted owl; 26 species of mammals, including the Yezo deer; 9 species of amphibians and reptiles, including the northern salamander; 34 species of fish, including the huchen; approximately 1,150 species of insects, including the Iijimaruboshi dragonfly; and approximately 600 species of plants, including sedges, reeds, marsh grass, sphagnum moss, and alder trees.

Until the 1960s, the Kushiro Marsh extended over almost the entire Kushiro Plain, except for the sand dunes and terraces in the south where Kushiro City is located, and the Kushiro Marsh was used synonymously with the Kushiro Plain. Its area is said to be 29,000 hectares (290 square kilometers). Due to development from the 1970s to the 1990s, the Kushiro Marsh is said to have decreased to 22,000-23,000 hectares. Of this, the portion that is considered "marshland," excluding farmland and forest, is even smaller, at 18,290 hectares (1985). Of this, 5,011.4 hectares in the center, which had been designated a bird and animal protection area, was designated a national natural monument (natural conservation area) in 1967 (Showa 42), and in 1980 it became Japan's first Ramsar Convention registered wetland. In 1987, the area registered under the treaty was expanded to 7,726 hectares, and 26,861 hectares including the surrounding area (of which 18,003 hectares were wilderness and water) were designated as Kushiro Marsh National Park.

However, despite these conservation policies, it has been pointed out that development, especially outside the designated areas, such as farmland and housing development, tourism development such as golf courses, construction of material storage facilities, road construction, and river improvement, is affecting the ecosystem. Since 1989 (Heisei 1), a conservation campaign has been carried out under the National Trust system. The species can be observed from Kushiro City Marshland Observatory, Hokuto Observatory, and Hosooka Observatory in Kushiro Town, and it is also possible to walk on the boardwalks constructed around the observation decks.

[Editorial Department]

"Kushiro Wetlands" (1990, Kushiro City) ▽ "Natural Observation of the Kushiro Wetlands" (1990, Nature Conservation Society of Japan) ▽ "Kushiro Wetlands - Unknown Creatures" (1993, Hokkaido Shimbun Press) ▽ "The Ramsar Convention and Japan's Wetlands" by Yamashita Hirofumi (1993, Shinzansha Psytech) ▽ "Kushiro Wetlands - Japan's Current Environment" edited by Honda Katsuichi (Asahi Bunko)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

北海道東部の釧路川、阿寒川(あかんがわ)の下流部一帯に広がる釧路平野の約80％を占める標高10メートル未満の低湿な泥炭地。釧路市と、釧路総合振興局管内の釧路町、標茶町(しべちゃちょう)、鶴居村(つるいむら)にまたがる。無数の中小河川が周辺の台地・丘陵から流れ込んで手のひら状の低湿地をつくり、シラルトロ沼、塘路(とうろ)湖、達古武(たっこぶ)沼などの海跡湖が東側を流れる釧路川沿いに並び、かつては深い湾入であったと考えられる。特別天然記念物のタンチョウや天然記念物のオジロワシ、エゾシマフクロウなどを含む鳥類約170種、エゾシカなど哺乳(ほにゅう)類26種、キタサンショウウオなど両生・爬虫(はちゅう)類9種、イトウなど魚類34種、イイジマルリボシヤンマなど昆虫類約1150種や、スゲ、ヨシ、ヌマガヤ、ミズゴケ、ハンノキなどの植物約600種で貴重な低層湿原の生態系を構成している。

　1960年代までは釧路市街地がある南部の砂丘・段丘地帯を除く釧路平野のほぼ全域に及んでいて、釧路湿原は釧路平野と同義に用いられてきた。その面積は2万9000ヘクタール（290平方キロメートル）とされる。1970年代から1990年代にかけての開発の影響で、釧路湿原は2万2000～2万3000ヘクタールに減少したといわれる。このうち、農地、森林などを除く「湿原」に当たる部分はさらに少なく、1万8290ヘクタール（1985）となっている。うち、鳥獣保護区に指定されていた中心部の5011.4ヘクタールが、1967年（昭和42）国の天然記念物（天然保護区域）に指定され、1980年日本で最初のラムサール条約登録湿地となった。1987年には同条約の登録地が7726ヘクタールに拡大されるとともに、周辺部を含む2万6861ヘクタール（うち、原野と水面1万8003ヘクタール）が釧路湿原国立公園に指定された。

　しかし、これらの保護政策の一方で、農地・宅地開発、ゴルフ場などの観光開発、資材置き場設置、道路整備、河川改修など、とくに指定区域外での開発が生態系に影響を及ぼしているという指摘もある。1989年（平成1）以後、ナショナル・トラスト方式による保護運動が行われている。釧路市湿原展望台、北斗(ほくと)展望台、釧路町の細岡展望台などから観察でき、展望台周辺に整備された木道の散策も可能である。

［編集部］

『『釧路湿原』（1990・釧路市）』▽『『釧路湿原の自然観察』（1990・日本自然保護協会）』▽『『釧路湿原―知られざる生き物たち』（1993・北海道新聞社）』▽『山下弘文著『ラムサール条約と日本の湿地』（1993・信山社サイテック）』▽『本多勝一編『釧路湿原―日本環境の現在』（朝日文庫）』

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