Other hydrological event

In the villages of Ogimi and Kunigami in northern Okinawa Prefecture, where hawksbill turtles, green sea turtles and loggerhead turtles are known to nest, an increasing number of eggs have been found destroyed by sea waves.
Coastal erosion has, over time, removed much of the sand from the beaches in question, which puts the turtle nests under threat from the elements.
Researchers are raising the alarm, saying that if the erosion of the beaches persists, there is a risk of the sea turtles — listed on the Environment Ministry’s Red List of endangered species — no longer laying eggs in the area.
“Ten years ago, there was sand this high up,” Kunio Komesu, gesturing at chest height to highlight the height of a bank at the edge of a beach in the Kijoka district of Ogimi in October. Komesu is a member of the Sea Turtle Association of Japan and has been researching sea turtles in the village for over three decades.
Currently, the bank, which appeared lower when there was more sand on the beach, is now seen towering above his head.
As more sand disappeared, a significant number of eggs were found damaged.
In 2005, a total of 2,118 eggs were found at the beach in Ogimi, out of which 1,078, nearly half, were confirmed to have hatched. In 2023, all of the eggs at the nine nests found at the beach since June 12 had been damaged.
In 2024, six nests were discovered but only two saw all their eggs hatch.
“The beach of Kijoka is a rare place where three species of sea turtle come ashore to lay eggs, but this year we haven’t even confirmed them laying eggs,” Komesu said.
According to him, the coastal erosion has resulted in the beaches becoming narrow and steep, forcing turtles to lay their eggs closer to the water’s edge.
As a result, the eggs buried in the sand are at greater risk of being damaged by waves or carried off to the sea.
The phenomenon has also been seen in Kunigami.
Muneyuki Kayo, another member of the sea turtle association, said the eggs of loggerhead turtles, which are laid near the shoreline, are especially vulnerable.
“The laying of eggs peaked in 2013 and the number has dropped due to the deterioration of beaches,” Kayo said. “There are places where the sand has completely disappeared, leaving only pebbles.”
Komesu cites offshore sand mining as one of the causes of the coastal erosion.
“The bank suddenly began to erode a few years after sea sand extraction started,” he said. “As sand is removed offshore, the sand at the beaches must have been drawn into the sea.”
The central government and the Okinawa Prefectural Government do not recognize that the beach erosion was caused by sand mining, instead attributing it to high waves and typhoons.
“If it was caused by high waves or typhoons, the sand couldn’t have been eroded so drastically,” Komesu said. “We want the authorities to suspend sand mining and conduct investigations, and take necessary measures including making the causes clear.”
According to the sea turtle association, the number of loggerhead turtle nests increased nationwide in 2012 and 2013, and the species' population appeared to recover. But their numbers have since dwindled and remain at low levels.
The number of green sea turtles has also been declining since 2020, the association said.