The rampant rise of red-eared terrapins is posing an ecological threat in a park in Nagakute, Aichi Prefecture.
The turtles have been rapidly breeding in a popular pond in Irigaike Park since being abandoned by their owners.
The 38,000-sq.-meter pond, originally used for agriculture, used to be surrounded by pastoral landscape. But it gradually turned into a residential area as urbanization progressed in Nagakute, the fastest-growing city in the prefecture.
In 1986, a park was built around the pond and became an popular leisure place for children and adults. Its population of red-eared terrapins had started growing near the end of the 1970s.
On sunny days, it is not uncommon to see rows of the pond turtles basking in the sun on rocks in the pond. But they’re about the only creatures left.
“Originally there was plenty of other marine life in the pond, like yellow pond turtles, catfish and turtlehead, but now it’s mainly just the red-eared terrapins that remain,” said resident Hisami Yamamoto, 83, who used to swim in the pond as a child. “Very few people remember what the pond used to be like.”
This particular breed of turtle is native to the Mississippi River and is commonly found downstream.
Young turtles are about 3 cm to 5 cm long and sold as pets in Japan. But they get a large as 30 cm when fully mature, and they also bite, so many owners eventually abandon them.
The turtles are strong breeders and omnivorous, and will eat the eggs of other turtle species.
In September, the Environment Ministry began considering banning the import and breeding of red-eared terrapins.
According to Aichi Gakusen University professor Takashi Yabe, who specializes in the ecology of turtles, the number of red-eared terrapins in the pond is estimated to be between 500 to 2,000.
“Irigaike is a closed environment, so it does not have a direct impact on other marine life in different environments,” Yabe, 50, explained.
“But if the pond overflows in the event of a heavy rain, the turtles may enter other habitats,” he warned.
In January 2012, Nagakute came up with a city development plan that aims for coexistence between agricultural communities and urban areas.
The first thing they did was to determine which natural environments need protection. This prompted an investigation by the city’s environmental department into the natural habitats of rare species in the region last summer.
During a city assembly meeting in September, a member asked: “After hearing the investigation report, what does the city plan to do with foreign species that threaten local ecology?”
“We have no choice but to remove those species in order to preserve the ecology,” a city representative said in response.
However, Yabe said that it is difficult to completely remove the turtles even by draining the pond because they can survive on dry land for months.
On Dec. 21, the city will hold a symposium on foreign species that includes experts and other citizens.
“I think the only solution is to control the number. With the help of the residents, we want to come up with ways to remove the turtles,” said a member of the environmental department.
This section, appearing Saturdays, features topics and issues from the Chubu region covered by local daily Chunichi Shimbun. The original article was published on Dec. 2.