Finless Porpoise Whales Circling the Ocean Surface

A Sea Designated for a Whale

On the map of Japan's national Natural Monuments, most entries name a tree, a cave, a colony of nesting birds. The Sunameri Kujira Kaiyū Kaimen — literally "the sea where finless porpoise whales migrate" — is one of the rare cases where the protected object is the water itself. A circle of sea 1,500 meters in radius, drawn around a single rocky promontory called Shirohana-iwa at the southern tip of an uninhabited island called Abashima, was inscribed in November 1930 as a place that belonged to a small grey whale.

The island sits just off the coast of Takehara in Hiroshima Prefecture, in the Seto Inland Sea. From the mainland it looks unremarkable: two low ridges divided by a saddle, the highest point only about a hundred meters above the water. There is no ferry. No one lives there. The designation was never really about the rocks. It was about what happens in the water around them between late January and early May, when the finless porpoises arrive to breed.

The Finless Porpoise — Sunameri

The Japanese name is sunameri, written with characters meaning "sand-smooth." English calls it the finless porpoise, and the name is literal — where most cetaceans carry a triangular dorsal fin, this small whale has only a low ridge running down its back to the tail. The head is rounded, with no beak. Adults reach 1.5 to 1.8 meters and weigh fifty to sixty kilograms, which makes them among the smallest of the world's roughly one hundred whale species.

Their range stretches from the Persian Gulf along the coasts of Asia. Within Japan, isolated populations live in Ise Bay, the Ariake Sea, the waters off Sendai, and — most numerous historically — the Seto Inland Sea. The Inland Sea population is treated as genetically distinct from the others; the animals do not appear to cross between regions.

Western Inland Sea fishermen had their own name for the porpoise: zegon, or zegondō. The Takehara dialect uses these terms still, though there are fewer and fewer occasions to.

Why a Sea Became a Monument

The designation in November 1930 was made under the criterion covering "animals or animal communities characteristic of a specific natural environment." What the criterion really protected, in this case, was a phenomenon. Each year in late January, finless porpoises began arriving in the waters off Abashima. By the equinox in late March, groups of fifty or more were swimming together in the small circle off Shirohana-iwa, breeding and feeding. By May they had dispersed back into the wider Inland Sea, and by autumn they were gone south.

Pre-war Japan recognized that this concentration — predictable, observable from shore, easy to study — was itself a kind of natural heritage. A 1930s travel guide noted that anyone could observe the social life of a whale group at this single spot during this single season, and the rarity of that opportunity was the point. To protect the porpoises one had to protect the sea they returned to.

It was an early and unusual decision. Most of Japan's "scenic and natural" monuments at that time were terrestrial: ancient trees, geological formations, specific cliffs. To draw a circle on the water and call it heritage required a different way of thinking about what could be preserved.

The Fisherman's Marker

Before 1930, the porpoises were not abstract. They were a working tool of the local fishing economy.

A traditional Inland Sea technique called sunameri-ajiro fishing used the porpoises as living indicators. The porpoises hunted sand lances — ikanago, small slender fish that bury themselves in sandy bottoms. When a sunameri pod swept through, the sand lances bolted upward in panic, and the predatory fish that fed on them — sea bream and sea bass — rose with them. The fishermen, reading the porpoises' movement on the surface, dropped lines into the disturbance and pulled in the larger fish that had been drawn up. The whales themselves were not targeted; they were partners. On Shirohana-iwa, the rocky cape at the center of the protected zone, fishermen built a small shrine to pray for a good catch — a quiet acknowledgement that the porpoises were sacred to the work.

That fishing method has not been practiced in living memory. The sand lance populations collapsed, the porpoises followed, and the technique disappeared with them.

Visiting Today

The reality of visiting Sunameri Kujira Kaiyū Kaimen has to be stated honestly. Abashima is private land, with no public access and no scheduled boats. The sea designated as the monument cannot be entered by tourist craft. And the porpoises that once arrived in groups of fifty are now reduced — according to Takehara City's own counts — to perhaps five or six visible animals. Sand lance numbers have not recovered. Sightings, even in the late-March peak, are far from guaranteed.

What can be visited is the marker on the mainland. On National Route 185, on the strip of coast just past the Takasaki tunnel and near Bamboo Park, a small hillock holds a stone monument and an interpretive panel called the Sunameri-hi. Stand on the rise and you look directly across the strait at the southern slopes of Abashima, with Shirohana-iwa just out of sight at its tip. The sea between the two is the monument. On a clear, calm morning in March, with binoculars, the patient watcher occasionally catches a dark back and a low ridge breaking the water before sinking again.

It is not a spectacular sighting. It is the kind of small, quiet evidence that the place still does what it was protected for, even at a fraction of the old scale.

Around Takehara

The monument lies on the Takehara coast, and the area has more rewarding stops than the porpoise sea alone. Five minutes by ferry from nearby Tadanoumi Port is Ōkunoshima, internationally known as "Rabbit Island" — a small national-park island overrun by feral domestic rabbits, with a darker history as a wartime poison-gas production site that the on-island museum addresses directly. The town of Takehara itself, a short drive inland, preserves a quarter of late-Edo merchant houses from its days as a salt-producing center; it is nicknamed "the Little Kyoto of Aki." Behind Tadanoumi rises Kurotaki-yama, a sharp rock peak laced with chain-handled climbing routes that delivers a panoramic view of the Inland Sea and its scattered islands.

Taken together, these stops give the porpoise monument context: it sits in one of Japan's most photographed inland seascapes, and the sense of a damaged, half-recovered marine environment threads through everything you see.