Invasion of the Turtles

Hi blog.

We’ve had some glorious weather, perfect for cycling to work.  The home trip is not quite as satisfying, mostly because of the tiny flying insects that swarm under the trees in the late afternoon and collide with my face.

I’ve spotted pheasants, both male and female, a masked palm civet, seen the feeding habits of crows, heard the cries of thrushes and bush warblers… pity that the ride ends at work!

I’ve seen the Mississippi red-eared sliders (Trachemys scripta elegans) too.  I’ve mentioned them in an older post, and have often wondered why the local governments don’t seem to be doing anything about them.

Alien invasion! Walk for you lives!

Then this article from the Japan Times made its way into my news feed:


Alien red-ear sliders greatly outnumber Japan’s own turtles



APR 26, 2016

Invasive red-ear slider turtles now vastly outnumber endemic Japanese turtles and are causing significant stress to the ecosystem, the Environment Ministry said Friday.

A study has put the number of red-ear sliders at 8 million, eight times the total population of endemic species.

Originally from the United States, the animals are widely kept as pets. However, they can grow to a considerable size and are often dumped in ponds and rivers when they outgrow their lodgings.

The species is known in Japan as midorigame and in some other countries as the red-ear terrapin.

“The growing population of red-ear slider turtles would mean the depopulation of insects, fish and other turtles that live on water weeds,” Masato Morikawa, an official in charge of monitoring alien species, told The Japan Times on Monday. “The population has gradually but continuously been increasing over the years.”

The species is believed to have been introduced after World War II. From the 1970s, the animals were widely sold at matsuri (festivals) and pet shops.

It is only one of several invasive turtle species now displacing local species.

The ministry said red-ear slider turtles have mainly colonized waterways in Kanto, Chubu and the Inland Sea areas. The entire population is estimated to consume up to 320 tons of water weeds each week.

Morikawa conceded that the need to control other alien species is more pressing as they can cause harm to humans: the poisonous red-back spider and the snapping turtle, which can bite off a finger, are among the priorities.

“At this point, the red-ear slider turtles are exterminated only in areas that are extremely overpopulated, but we are strengthening measures against them,” he said.

The ministry plans to restrict imports, crack down on the abandoning of pets and step up culls.

Article ends.

The writer did make a noticeable mistake in the article – baby red-eared sliders are known as midorigame whereas the species is known as akamimigame or, more correctly, mishishippi akamimigame.

Many people are unaware that it is not a native species.  Others simply take the dichotomal view that it is “foreign” as opposed to “Japanese” – rather than the infinitely more accurate and helpful “introduced” or “feral” as opposed to “native”- and therefore has some natural advantage.  (Much the same way foreign-born sumo wrestlers somehow have an unfair natural advantage… because…  er… reasons)

Red-eared sliders do have certain advantages in this case.  Firstly, they mature at an earlier age than the native turtles they compete with.  They also grow larger, enabling them to successfully compete for basking and nesting space, plus acting as a deterrent against would-be predators.  Thirdly, they are omnivores – the young have a tendency towards carnivorous habits while older turtles prefer plant material – and will feed on either plant or animal matter as need dictates.  Finally, the Japanese suburban and semi-rural environments lack predators that significantly impact their population.  The Mississippi red-eared slider’s natural enemies include alligators, raccoons, and skunks, all missing from the Japanese ecosystem.  Foxes and badgers may prey upon young turtles, but these are noticeably absent from most suburban environments.

My take: The reason for these turtles damaging the environment can be put down to human irresponsibility.  No kind of permit is required to buy the babies sold at shops or even stalls.  A lack of understanding of the responsibilities involved (“What?  I’m supposed to look after this for the next 30 years?”) plus a complete absence of any understanding of the biology of the sliders – like that they don’t remain babies forever.

They start off small, cute and green… but grow to be not small, not cute and not green.

I really have a disdain for killing reptiles, but I feel that culling will be the only way to control their numbers, in addition to banning further imports and restricting ownership.

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