Kushiro Wetlands
Many rare and native species of plants and animals inhabit the Kushiro Wetlands, including Japan’s only known population of the endangered Japanese crane (Jp. tancho; Grus japonensis), as well as species that have been in the area since the last ice age. The primitive lowland environment, forming the largest wetland area in Japan, has changed little since sea levels fell around 6,000 years ago. The Kushiro Wetlands are protected under the Ramsar Convention, an international treaty for the conservation of wetland areas.
The glacial period
Around 30,000 years ago, during the coldest part of the last ice age known as the Wisconsin glaciation, sea levels were 100 meters lower than they are now. At that time, a land bridge connected Hokkaido to the Eurasian continent through the island of Sakhalin, allowing animals to migrate from the continent to Hokkaido. Over several millennia, temperatures rose, causing glaciers to melt and sea levels to rise, and the area that is now the Kushiro Wetlands became a bay.
Changing seas
Some 6,000 years ago, temperatures and sea levels dropped again, and this low-lying area became landlocked. Prehistoric societies left mounds of discarded shells along a plateau bordering the wetlands. These shell mounds show how sea levels have changed over time, indicating that the coastline was once further inland. Several lakes and water reservoirs remained after the sea retreated.
