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Hidakasanmyaku Erimo Tokachi NP, Hokkaido
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Dozens of reefs stretch 1.5 km southeast, making Erimo Japan’s largest harbor-seal haul-out. It is also the seals’ southernmost range in the western Pacific, with roughly half of Japan’s population living around the cape.
In a 19th-century travel record, Matsuura Takeshirō wrote that kelp growing on Cape Erimo’s reefs was called “the gods’ beard” and left unharvested—a striking record of the cape’s sacred significance to Ainu people.
Deforestation sent red soil 10 km offshore, damaging Erimo’s seaweed beds. Restoration began in 1953; workers covered seeds with washed-up seaweed to keep them from blowing away. As the forest returned, so did kelp and fish.
Reef grounds around Erimo yield Mitsuishi kelp, sold nationwide as Hidaka kombu. On harvest days, families spread boatloads over gravel yards for same-day sun-drying; the long leaves are then cut into 105-cm lengths.
Though the reefs look like the Hidaka Mountains sinking offshore, they’re made of the separate Erimo Formation—sandstone, mudstone and conglomerate. Fossils revealed a Late Oligocene age, overturning an earlier Miocene assignment.
The cape’s Ainu name, Onne-enrum, means “great projecting headland.” Ainu-derived names also mark reef places used for kelp harvesting; a local study records Tokkari-kukido, the channel seals use.
The same Mitsuishi kelp has different forms on opposite sides of Cape Erimo, and four kinds of kelp grow near the tip. One short stretch of coast holds a surprisingly varied underwater plant community.
Two old travel writers spotted a mouse in the cape’s outline: Matsuura Takeshirō described it as a crouching mouse from afar, while Tani Gantan likened the slim rocks offshore to its tail.
