The population of snapping turtles has surged around Inba Pond in Chiba Prefecture increasing concerns that the alien species may pose a danger to humans and harm the local ecosystem.

Snapping turtles, which inhabit a wide area from southern Canada through South America, have been imported as pets since the 1960s. Some have evidently made it into the wild.

In mid-June, local fishermen around Inba Pondcaught 44 snapping turtles, including in rivers neighboring the lake.

Snapping turtles prey on fish, birds and weeds and can grow to be as big as 1 meter from nose to tail and weigh some 35 kg. They can cause serious injuries if they bite humans.

Out of concern about possible adverse effects on the ecosystem, the Environment Ministry designated snapping turtles an alien species in 2005, banning their import and breeding.

“By the time an increase in the population of snapping turtles is noticed, there is likely to have been considerable damage to the ecosystem already,” said Hideaki Kato, an instructor specializing in conservation biology at Shizuoka University.

“Governments should understand that this is a pressing issue and should quickly move to grasp the situation,” Kato said.

The population shot up around Inba Pond in particular because the area has a large number of embankments that provide a suitable spot for the turtles to lay eggs.

In its survey for fiscal 2004 to 2005, the Chiba Prefectural Government found some 1,000 snapping turtles, the most of any prefecture.

The prefectural government has also received reports of local children being bitten and fishing nets being cut.

It started hunting the species in full swing in fiscal 2007 and has caught a total of around 3,000. Since snapping turtles hide in water without moving for hours, many likely escape the traps.

The turtles are also highly fertile, laying 20 to 30 eggs at a time.

“We keep catching them, but their number won’t decline,” a local fisheries association official said. “It’s like a cat-and-mouse chase.”

The prefectural government was aiming to collect eggs during June, seeing it as one effective countermeasure.

But it said the eggs are hard to find as the species travels over a vast area.

Making matters worse, it is difficult to secure a sufficient number of volunteers to gather the eggs.

A recent study has indicated that snapping turtles live in other areas such as the Kano River in Shizuoka Prefecture. Some have also been spotted around Shinobazu Pond in Tokyo’s Ueno area.

An Environment Ministry official said that breeding sites may have already spread across Japan.

But officials in the Shizuoka Prefectural Government said they are busy hunting other alien species, such as raccoons that eat away at local farm products, and that there is no time or human resources left for dealing with snapping turtles.

Lacking detailed knowledge of the situation, other prefectural governments appear uncertain about what to do to control the snapping turtle population.