Tradition: Japanese Mythology
Alternative Names: Umishika
Category: Deer
The Myth
Umishika, meaning “sea deer,” are dangerous sea monsters said to inhabit the open waters south of Japan, particularly around the island of Yakushima and off the southern coast of Kyūshū. Because they live deep beneath the sea, little is known about their appearance. Fishermen who encounter them describe seeing dark, shadowy forms lurking beneath the waves. They are greatly feared by the island’s fishermen.
Umishika are carnivorous and prey on medium-sized fish such as skipjack tuna. They are also aggressive toward humans and will attack fishing boats that enter their feeding grounds.
According to a legend from Yakushima, the umishika are responsible for the taboo against fishing on the sixteenth day of the fifth month of the old lunar calendar.
Long ago, the sixteenth day of the fifth month was considered a holy day belonging to the mountain gods. On that day, all the gods and spirits of the mountains gathered together for a great banquet, and villagers were forbidden from entering the mountains.
One year, however, a fishing boat from the village of Issō went out onto the open sea northwest of Yakushima to catch skipjack tuna. A huge number of fish were swimming close to the surface, and the fishermen were certain that a large shoal was nearby.
When they reached the spot, the fishermen were delighted by how easily they could catch fish. They pulled one tuna after another from the water.
Suddenly, a huge dark shape appeared beneath the surface. One of the elder fishermen recognized the danger and cried out, “It’s an umishika!”
The fishermen immediately pulled in their lines, raised the sails, and prepared to flee toward shore. But the umishika had already noticed them.
The monster pursued the boat, diving beneath the waves and appearing again between the swells. The wind made it difficult for the fishermen to escape, while they rowed with all their strength. They attempted to slow the creature by throwing all of the tuna they had caught into the water behind the boat, hoping it would stop to feed on them.
The tactic failed. Before long, the umishika had caught up with them.
As the monster prepared to climb aboard the boat, one of the fishermen seized an oar and thrust it with all his strength into the creature’s open mouth. The umishika recoiled and fell back into the sea, abandoning its pursuit.
The fishermen rowed continuously toward shore, exhausted by their struggle but grateful to have survived.
Afterwards, the villagers decided that the prohibition on the sixteenth day of the fifth month should apply not only to the mountains but also to the sea. From then on, hunters and fishermen remained at home on that day, making offerings and holding festivals for the gods of the mountains and the sea.
Sources
“Umishika.” Yokai.com: The Japanese Yokai Encyclopedia. Accessed September 5, 2026. https://yokai.com/umishika/