ALIEN SPECIES IN JAPAN: FISH, TURTLES, MONGOOSES, RACCOONS, NUTRIA

ALIEN ANIMALS IN JAPAN:

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Tanukis threatened by American raccoons Alien animals, indigenous to places outside of Japan, have caused havoc in Japan. They have disrupted the local ecosystem and threaten indigenous wildlife. Among the animals that have shown up are alligators, piranhas and goats. About 2,000 alien species are found in Japan, including snapping turtles, nutria, largemouth bass and smallmouth bass.. Alien species are designated by the Alien Species Law as invasive alien species. The importing, releasing or raising them can be imprisoned and/or fined.[Source: Japan News, October 2016]

Alien species are animals and plants brought from another country and released into local natural environments. They can harm indigenous species, and efforts have been made across Japan to eliminate them. Alien animals are a threat everywhere but Japan is particularly vulnerable to them because it has a delicate island ecosystem with unique species that have not faced threats from competitors like animals living on the continents. Alien insects present many problems. They can damage the environment and farms. Rare cross breeds of stag beetles have been released, threatening local species.

Masked civets brought in from Southeast Asia, nutria from Latin America, minks from North America and golden-backed tree squirrels and Taiwan squirrel have all caused crop damage and threatened local species. Feral goats are blamed for eating rare plants on Japanese Islands. Siberian weasel introduced to Japan in some places are displacing Japanese natives. Rabbits set free by pet owners are blamed for eating rare kinran orchids in the Tokyo area. Yellow-legged hornets native to China, Taiwan and Southeast Asia have harmed people and caused damage to the bee-keeping industry. They eat insects, including honeybees, and muscle out native species of hornets

List of Alien Species in Japan Online Resources, National Institute for Environmental Studies, Japan nies.go.jp

Invasive Species and Japan

In Wakayama and Aomori prefectures, Taiwanese macaques have established themselves and hybridized with native Japanese macaques, “contaminating” the gene pool of the native species. In Tokyo and Chiba Prefecture, there are populations of snapping turtles, released by people who purchased them as pets. These turtles attack and eat native freshwater animals. The fall webworm, the caterpillar of a kind of moth has devastate native trees. [Source: Rowan Hooper, Japan Times, May 17, 2014]

Green anoles are a kind of lizard native to the southeastern part of the U.S. that was introduced to the Bonin Islands during the mid 1960s (Chichijima), early 1980s (Hahajima) and late 1980s (Okinawajima). The animals are believed to have been pet animal and/or hitchhiked with U.S. military forces. They have preyed on endangered native insects and competed with native lizard. Many endemic insects on Ogasawara have been seriously damaged by the predation, and some species are nearly extinct on Chichijima and Hahajima islands.

Hard clams — a species native to North America and the basis of clam chowder — are thriving in Tokyo Bay. They were first found in the 1990s and likely arrived in the ballast of commercial ships. In the 2000s, there were a number of unexplained kangaroo sighting in the woods around Asaki in Miyagi Prefecture in northern Honshu. The area is regarded as too cold for kangaroos.

The Bonin Islands of Japan are overpopulated with Giant African snails. These five-inch mollusks were introduced from east Africa in the 1940s as a folk medicine for everything from tuberculosis to kidney trouble and were given to Japanese soldiers in World War II. In some places the snails are so numerous it is hard to take a step without crushing one of their shells. They do have one attribute: they are an early warning signal for storms; whenever a typhoon is coming the head for higher ground.

Pests that originated in Japan that have caused problems around the world include: 1) tiger mosquito, thought to have entered the United States in a shipment of used tires; 2) tsugakasa aburamushi, a hemlock-killing aphid thought to have entered the United States in a shipment of hemlock wood from Japan; and 3) brown marmorated stink bugs, dime-size shield-shaped creatures that give off an unpleasant smell when squashed or irritated. The latter first arrived in the United States in Allentown, Pennsylvania in 2001 and are now found in 29 states.

Nutria and Mongooses in Japan

Nutria (Coypus) are small mammals that look like a cross between a beaver and a rat. Native to South America, they were introduced to Japan in the 1930s and bred for their fur, which was used to make winter clothing for the military. Some of the animals were let go or escaped and bred quickly because they have no natural predators. Now they are particularly plentiful in Tottori Prefecture where they are blamed for damaging crops. They have become such pests there that the local government pays a ¥2,000 bounty for every one killed.

The main predator of endangered Amami rabbits on Amami island are mongooses (Herpestes javanicus), which were introduced to Amami Oshima Island south of Kyushu to kill venomous habu snakes (Protobothrops flavoviridis) in 1979, but has since become a bigger problem than the native snakes.

After they were introduced the mongooses population exploded, eating many native animals, such as the rare Amami rabbit, but largely leaving snakes alone. This is because the mongooses are primarily diurnal animals and the snakes are nocturnal. The first mongooses in Japan were brought to Okinawa in 1910 to control rats and habu snakes there. Mongooses are native to West Asia and Southeast Asia. They preferred other prey and ate threatened species such as Okinawa rails. Rats and habu snakes have continued to thrive while less hardy native species have suffered.

Mongooses are generalist predators of many terrestrial animals, such as Amami rabbits. Some small animal populations increased in the presence of mongooses, due to trophic cascade effects (mongooses ate the middle level predators, which normally preyed upon the smaller species) but most small mammals (including Amami rabbits), dramatically decreased in areas where mongooses were present. The number of captured mongooses in the northern area or Okinawa rose from around 50 in 2000 to almost 600 in 2007 and declined to 127 in 2014. [Source: Japan News, October 2016]

Rascal and the Introduction of Raccoons in Japan

Araiguma Rasukaru

North American raccoons, imported as pets in the late 70s following the success of a popular animated series about a boy and his pet raccoon, now range in large numbers across Hokkaido and other places. Jason G. Goldman wrote in Nautilus: Our story begins when a young Wisconsin boy named Sterling North adopts an orphaned baby raccoon and names him Rascal. The boy and the raccoon were inseparable as best friends, and for a year they did everything together. The true story of Sterling North and Rascal the raccoon formed the basis for North’s award-winning 1963 memoir, “Rascal: A Memoir of a Better Era”. In 1969, Disney would go on to create a feature film based on the book, predictably called Rascal, and a 52-episode anime series called Araiguma Rasukaru, based on the book, aired in Japan throughout 1977. [Source: Jason G. Goldman, Nautilus, Science Connected, September 18, 2013]

“Once upon a time, raccoons were strangers to the island of Japan, save for the occasional critter kept in a zoo. That all changed when Araiguma Rasukaru aired and turned a nation onto raccoons’ inherent charm. “Its round, funny face with a bandit’s mask across the eyes and a striped bushy tail create a humorous impression,” writes Japanese researcher Tohru Ikeda of Hokkaido University, “and people find its habit of washing of food prior to eating curious.” Suddenly, every Japanese child wanted their own pet raccoon, like the boy hero of the cartoon. At the peak of their popularity, Japan imported more than 1,500 North American raccoons each year. And while the government eventually banned their import and the ability for Japanese citizens to keep them as pets, it was too late.

“Life imitated art when some of the Japanese children who had kept pet raccoons released their pets into the wilderness, like the boy in the cartoon and the real-life Sterling North before him. Other raccoons, being wild animals and not domesticates like dogs, cats, or horses, simply escaped. Still others were released out of frustration by their owners. Raccoons, like chimpanzees, are friendly when young, but as they age they become more aggressive, harder to control, and pose a potential threat to humans. Raccoons, like chimpanzees, are simply not suitable pets.

Raccoon Pests in Japan

With no natural predators, they breed freely, eat corn, other crops, chickens and ducks and defecate and urinate and set up nests in the attics of houses. Raccoons threaten foxes and the nests of grey herons and other birds. They are particularly threatening to tanukis (raccoon dogs), which are of similar size and look kind of similar. Raccoons have severely injured tanukis in fights and have aggressively claimed their food, causing tanuki populations to drop. Raccoon running loose in Kyoto temples are blamed for making holes in roofs, knocking over Buddha statues and eating goldfish in World Heritage Site temples. A campaign has been launched to exterminate them there and other places. Wildlife people catch raccoons using a mixture of dog food, caramel corn and sugar-coated, fried bread as bait.

Jason G. Goldman wrote in Nautilus: “Raccoons have proliferated in Japan, where they have no natural predators, and by 2004, they had spread at least 42 of 47 prefectures.. In some parts of the country, they invade cattle farms, where they feed on the same corn that gets fed to cows, and find safe spaces for reproduction in the tall grasses of grazing pastures. In other places, fish farms provide them with a veritable buffet. The animals damage crops across the food pyramid: corn, melons, strawberries, rice, soybeans, potatoes, oats, and more. [Source: Jason G. Goldman, Nautilus, Science Connected, September 18, 2013]

Raccoons have taken a toll on the ecology of Japan, preying on native mammals like the gray red-backed vole, along with snakes, frogs, dragonflies, damselflies, butterflies, bees, cicadas, and shrimp and other shellfish. They hunt the Japanese crayfish, a species classified as vulnerable by the Japanese Ministry of Environment, and the Tokyo salamander, which is threatened. They compete both for food and for territory with the native tanukis and the red fox, and push native owls out of nesting spots in hollow trees. Ever since raccoons attacked a reproductive colony of grey herons in Nopporo Forest Park in 1997, the grand birds have not returned to their historic breeding grounds. Raccoons are also important vectors for the spread of infection diseases. They’re known to carry rabies, and a 2011 report in the Journal of Parasitology even found evidence for the potentially dangerous and brain-altering parasite Toxoplasmosa gondii in raccoon droppings.

Damage Caused by Raccoon in Japan

captured raccoon

The amount of damage to agricultural products caused by raccoons rose from near zero in 2000 to 330 million yen in 2014. There have been many cases of damage to corn and watermelon crops. [Source: Japan News, October 2016]

Jason G. Goldman wrote in Nautilus: “ In 2004 Ikeda and colleagues estimated that raccoons were responsible for more than thirty million yen (approximately US$ 300,000) worth of agricultural damage each year on the island of Hokkaido alone. Raccoons have also adapted to city life in the more urban parts of Japan, where they nest in air vents beneath floorboards, attic spaces of older wooden houses, Buddhist temples, and Shinto shrines. In cities, raccoons forage by going through human garbage, and hunt carp and goldfish that are kept in decorative ponds. [Source: Jason G. Goldman, Nautilus, Science Connected, September 18, 2013]

“Following the passing of a law protecting native Japanese ecosystems in 2004, local governments began the culling of invasive raccoon populations. That year, Reiji Yoshida wrote in the Japan Times that Hokkaido would kill 2,000 raccoons each year. Predictably, there was public backlash to the harming of these cute, furry animals. “When the Kanagawa prefectural government announced the raccoon eradication plan in 2005, comments from the public revealed a wide range of opinions, including preference for control over eradication, negative response to lethal methods, skepticism of success, and opposition toward using great amounts of tax revenue for the plan,” said Harumi Akiba and colleagues in a 2012 paper in the journal Human Dimensions of Wildlife. Indeed, according to their survey of Kanagawa prefecture residents, only 31 percent of the population supported the complete eradication of invasive raccoons in Japan. Further, they discovered that Araiguma Rasukaru no longer held sway over the public perception of raccoons. More than half of the study participants had seen the series, but Akiba’s statistical models showed that it didn’t influence peoples’ support or rejection for raccoon culls. The anime series that had originally instigated the raccoon invasion itself has lost its control over public opinion.

Feral raccoons have hindered the nesting of Ural owls native to Hokkaido. A team, led by Hokkaido University professor Itsuro Koizumi, conducted research on the owls and raccoons in Nopporo Forest Park near Sapporo. Raccoons are good at climbing trees and sometimes use tree hollows to raise their young, as birds do. The team studied 341 tree hollows of more than 10 centimeters in diameter in the park by installing tiny cameras in 2011-12. Based on fur and feathers left at cavities as well as past photos, the team found that 37 hollows were occupied by raccoons and 34 by owls. Four of them were used by both creatures in different years according to the results of its study. [Source: Daily Yomiuri, December 28, 2013]

Civets in Japan

Masked palm civets are known as hakubishin in Japanese. With lifestyle patterns similar to those of raccoons, they are omnivorous and primarily nocturnal creatures that often make their homes under roofs or floorboards of people’s houses. They are not native to Japan and are thought to have been introduced from China. They live mostly in villages in valleys in mountainous areas. Masked palm civets have been blamed for causing extensive crop damage in Saitama Prefecture.

masked civet in Japan

Masked palm civets (Paguma larvata) are the most widespread of all civets. They range from northern Pakistan and Kashmir in the west to much of eastern and southern China in the east and southwards through Vietnam, Myanmar, Laos Cambodia and Thailand in Southeast Asia to the to the Malay Peninsula and Sumatra and Borneo in Indonesia. Among the islands found in their range are Taiwan, Hainan, and the Andaman and Nicobar Islands. Humans introduced this civet species to the Japanese islands of Honshu and Shikoku. Genetic studies indicate that those in Japan were introduced multiple times over the centuries, with at least two from Taiwan. [Source: Wikipedia, Barbara Lundrigan and Steve Baker, Animal Diversity Web (ADW) /=]

Masked palm civets are found in deciduous, evergreen, scrub and mixed deciduous forests, as well as in tropical rainforests, mountainous regions and near human settlements. They civets are omnivorous (eat a variety of things, including plants and animals), mainly eating fruits, but also consuming eat small vertebrates, insects, and birds. These civet have lived up to 20 years in captivity, but probably average about 10 years in the wild. /=\

Alien Fish in Japan

Alien fish which have shown up in Tamagawa River in Tokyo included piranhas, tiger oscars and silver arowana from the Amazon, alligator gars from North America, crown loach from Indonesia and polypterus palmas from Africa. Most of are believed to have originated in household aquariums. The Environment Ministry decided to launch a full-scale extermination program at two ponds in a national park in Hokkaido that were under threat from two foreign tropical fish — guppies and tilapias.[Source: The Japan News, November 3, 2013]

Black bass and blue gills, introduced from the United States, have increased rapidly in Japanese lakes and squeezed out indigenous fish such as “koi” (carp) and “funa” (crucian carp). Other introduced species such as American channel catfish, which can reach a length of four feet, and alligator gars, aggressive fish with big teeth, also threaten local fish. In some rivers there are large populations of guppies that have bred from pet fish left in the river. Alien species found in the Tanawa River which empties into Tokyo Bay include black bass and tropical fish such as guppies and arowana. The Northern Pacific starfish, a species native to waters off Japan, has been carried in ballast water in Japanese ships to Australia, where it has damaged fish farms.

Alligator gars are native to North America and can reach lengths of three meters, making them one of the world’s largest freshwater fishes, With a mouth that somewhat resembles an alligator, it has been found in the moat of Nagoya Castle and other places. It has been designated an alien species. [Source: Japan News, October 2016]

Black bass (also known as large mouth bass) are a favorite catch for fishermen in the United States. They were intentionally released in Japan by fishing enthusiasts and bait salesmen as well by some local organizations hoping to attract fishermen. Black bass can lay eggs up to three times year and they are voracious carnivores that feed on the eggs and fry of other fish. The first black bass were reportedly brought from California and placed in Lake Ashi near Tokyo in 1925 by a fishermen who found them sporting to catch. Over the years more were introduced and spread, with some even finding their way into the moat around the Imperial Palace.

Blue gills are fast-reproducing and highly adaptive fish that feed on the eggs of indigenous fish. It is not uncommon to see children with a bucketful of them after a day of fishing in a local canal or lake. They have been intentionally released by fishing enthusiasts and bait salesmen because they are easy to catch and grab at almost any bait. The first blue gills were reportedly given as a gift in 1960 to the crown prince of Japan by the mayor of Chicago.

Among the species adopted for the “if you can’t beat ‘ em, eat ‘m” strategy are channel catfish which are fried and made into catfish burgers and crawfish which are used to make capriccio, salads and soups. Both species are native to North America. In some places the channel catfish are sliced up as sashimi and marketed as “river fugu” (fugu is the famously toxic puffer fish, which is regarded as delicacy in Japan).

Alien Fish in Lake Biwa

red-eared slider

The problem with foreign species is particularly acute in Lake Biwa, Japan’s largest lake, near Kyoto. Thirty-five species of foreign fish have been caught by local anglers while numbers of indigenous fish have declined. By some estimates blue gills now make up 80 percent of the lake’s total fish population. One a fishermen who caught 300 fish in one spot said all the fish he caught were blue gills.

The problems has become so worrisome the local authorities have introduced harsh penalties for anyone caught releasing foreign species and set up patrols to look for them. In April 2003, a new law took effect that penalized any fishermen for releasing a foreign fish after it is caught. Fishermen sharply opposed the ban. They say that releasing bass after they are caught is a fundamental aspect of bass fishing and that bass don’t cause a serious problem the blue gills do. About $2 million a year is spent on trying to get rid of blue gills in Lake Biwa.

Catching heaps of black bass and bluegills is fine but what do you do with all the unwanted fish? Recipes for bluegill sushi and fermented bluegill have been introduced on website to encourage people to eat the fish. A company called Suzuki Shofudo has come up with the rather novel idea of carbonating the fish by steaming them for a day and letting them dry out until they are black and selling them as deodorizers that are said to be more effective than even the best charcoal filters.

Alien Turtles and Crawfish in Japan

These days one of the most commonly seen turtles in Japanese ponds is the Mississippi red-eared slider, a species native to North America that many Japanese buy when they are young as cheap house pets and then release into ponds when they grow up. The same is also true with snapping turtles introduced to Japan. Huge ones, weighing 10 kilograms, have been found in the Imba Marsh in Chiba. In June 2009, a 37-kilogram alligator snapper was caught in a river in the middle of Nagoya near Nagoya Castle.

Called midori game in Japanese, red-ear sliders (a kind of turtle native or north America) were widely sold at pet shops and stalls. Many were released into rivers and ponds by people who could not raise them. They grow rapidly and out-compete native species. As of 2015, there were about eight million red-eared sliders and 980,000 Japanese pond turtles, who have been threatened by urban development and muscled out by the sliders, who thrive in all area of Japan and do well in urban areas. An import bans and regulations on sales are being introduced gradually to avoid a surge of abandoned pets. Imports of various kinds of turtles from the U.S. declined from over 600,000 in 2002 to 67, 691 turtles in 2015. [Source: Japan News, October 2016]

Crawfish from the United States were introduced to feed the frogs. They too escaped are bred and multiplied and are now one of the most numerous species in Japan, found throughout Kyushu and Shikoku and everywhere on Honshu except the northern part of the island. Crawfish have thrived in places were local fish and crabs have been wiped out by declining water quality. They are an important food source for weasels and birds such as egrets and kingfishers.

The signal crayfish is an alien species from North America released is Lake Mashu in Hokkaido in 1930. Conservationists blame it for driving local species of crayfish but gourmet value it as a tasty food often referred to as lake lobster.

Alien Frogs and Toads in Japan

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One of the most commonly seen frogs in Japanese ponds is the American bullfrogs. These behemoths were first introduced to Japan in the early 20th century as poor farmers were looking for new ways to make money and thought they could boost their incomes by exporting frog legs. The program worked. Farmers did make some extra cash but some frogs escaped from ponds and began breeding and multiplying in ponds, rice paddies and irrigation canals. The bullfrogs don’t appear to have disrupted local ecosystems too much. They prefer ponds while indigenous Tokyo daruma pond frogs favor irrigation canals.

Poison marine toads, native to South America and similar to cane toads brought to Australia, were brought to Ishigaki island in Okinawa to combat pests that damage the sugar canes crops there. They have multiplied quickly and spread to Iriomote island, where they present a threat to Iriomote cats who may eat the toad’s poisonous skin.

Cane toads — creatures that have caused major havoc in Australia after being introduced there — are also taking over Ishigakijima Island in Okinawa Prefecture. The toads — which are 8 to 16 centimeters long and produce a strong toxin — are vociferous eaters and lay up 50,000 eggs at one time. The toads were introduced to the island in 1979 to help exterminate a scarab beetle that damages sugar cane.

Getting Rid of Foreign Species Can Cause Unexpected Problems

Kunio Kobinata wrote in the Yomiuri Shimbun:“Recent research has found that exterminating alien species can have unpredictable, harmful effects on local ecosystems and governments are now reviewing its methods due to the unpredictable side effects extermination can engender. In a western area of Ichinoseki, Iwate Prefecture, bullfrogs native to North America were spotted from the 2000s in storage reservoirs in farming areas. They have eaten wrinkled frogs and other indigenous species in village forests, causing drastic declines in their populations. Normally hundreds of wrinkled frogs could be found in a single pond. [Source: Kunio Kobinata, Yomiuri Shimbun, August 31, 2014]

“Prof. Tadashi Miyashita of the University of Tokyo, an expert in ecological science, said just a few American bullfrogs in the same pond can nearly eliminate the wrinkled frogs. “Kubogawa Iihatobu Shizen Saisei Kyogikai, a citizens organisation working to revive the natural environment in the area, began exterminating American bullfrogs in reservoir ponds in late June. When members used nets to scoop out one pond, they caught more than 200 American bullfrogs in 10 minutes but only a few wrinkled frogs. "Though the process is daunting, domestic species will go extinct unless we continue," said 27-year-old member Ryohei Sato, who participated in the work.

“Carp had also been released into reservoir ponds for farming or ornamental purposes, living alongside the bullfrogs. Most of the fish came from China, however, so Sato worked to exterminate them as well. However, research conducted on the site by a team led by Miyashita showed that the carp had eaten bullfrog tadpoles, even though both were alien species. The carp were indirectly protecting the indigenous wrinkled frogs. Ponds with carp had less than half as many American bullfrogs as ponds without the fish. In experiments inside water tanks, the carp ate three times more American bullfrog tadpoles than wrinkled frog tadpoles. The wrinkled frog tadpoles are believed to be hard to spot because they are hidden in waterweeds. If the carp are exterminated, the number of American bullfrogs could increase.

“Miyashita’s team conducted biological research in reservoir ponds in Namegawa, Saitama Prefecture, before and after it exterminated black bass, a freshwater fish species that is native to North America. After the extermination, there was an explosion in the population of red swamp crawfish, which the black bass had preyed on, and they consumed water chestnuts and other indigenous waterweeds with abandon, causing a drastic decrease in the number of waterweeds. The population of an indigenous damselfly species also nosedived as the indigenous insects lay eggs on the waterweeds.

Goats in the Ogasawara Islands

Kunio Kobinata wrote in the Yomiuri Shimbun:“On the Ogasawara Islands, which are a World Natural Heritage site, goats that were brought to the islands as livestock in the 19th century escaped and became wild. They ate and damaged indigenous plants on the islands. [Source: Kunio Kobinata, Yomiuri Shimbun, August 31, 2014]

“The Tokyo metropolitan government began exterminating the goats, and they have been almost entirely wiped out except for those found on Chichijima island. However, as a result, an alien species of tree called she-oaks and lead trees spread on Anijima island. The trees were originally planted on the island to be later used as fuel. The trees now cover most of the island. Because the goats disappeared, the alien plant species with its strong reproductive power drove away indigenous plant species and expanded its habitat. The central government joined the efforts of the metropolitan government in exterminating the alien plant species.

“Prof. Naoki Kachi of Tokyo Metropolitan University, an expert on ecological science, said: "It’s inevitable that priority is placed on the goats, which cause the most significant harm to the ecosystem. However, we have to consider how many alien species need to be exterminated to minimise the impact on indigenous species. The only way is to proceed while checking the effects of our actions."

Image Sources: Japan-Animals blog, Wikimedia Commons

Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, Daily Yomiuri, Yomiuri Shimbun, Japan National Tourist Organization (JNTO), New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, BBC, CNN, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.

Last updated March 2025