Islanders aim to stamp out poisonous toads
BY YUMI NAKAYAMA
THE ASAHI SHIMBUN
ISHIGAKI, Okinawa Prefecture--Introduced to this subtropical island to combat insects damaging sugar cane crops, the cane toad is today a far greater environmental pest than the creatures it was meant to stamp out.
Operations are under way to cull the toad, a voracious feeder that secretes potentially lethal toxins when attacked, and prevent it further damaging the island's ecosystem.
The population of the amphibian soared to an estimated 30,000 to 50,000, comparable to the human population of 45,000, in the 31 years since it was introduced from a nearby island.
Islanders and researchers fear the toads, which can devour huge quantities of insects, could upset the natural balance of Ishigakijima island, part of a national park, as they compete for food with other animals, including amphibians.
They are especially concerned that cane toads could inundate neighboring Iriomotejima island, posing a risk to the Iriomote yamaneko, a wild cat designated for special protection by the central government. The endangered cat preys mainly on insects, lizards and rats, but occasionally eats toads.
Preying on a cane toad could be lethal to the Iriomote Yamaneko because of the amphibian's strong venom.
Islanders say dogs and snakes have died after swallowing the toads.
Originally from Latin America, cane toads inhabit ponds and rice paddies, breeding throughout the year.
Growing to 8-15 centimeters, it typically preys on insects, but has also been known to eat snakes and rats.
It secretes poison from the skin behind its ears when threatened.
The main component of the venomous substance is bufotoxin, which is powerful enough to cause cardiac arrest in mammals and other vertebrates.
The toad was designated as an introduced pest species in 2005 and there are regulations on keeping and disposing of the creature.
One night in late July, all 39 students, their parents and teachers at Ibaruma Junior High School in the northern part of Ishigakijima gathered in the school gym for a special lesson on cane toads.
Equipped with flashlights, work gloves and plastic bags, they were scheduled to go out and catch the unwelcome toads later that night for the first time.
Itsuha Katsube, an official with the Ministry of Environment Ishigaki Ranger Office, opened the session by explaining the life of the amphibian.
"Cane toads across Ishigakijima island devour the equivalent of 600 kilograms of insects a month," Katsube said. "One toad lays a whopping 10,000-50,000 eggs at a time."
When they went outside, a girl cried, "I've found one!" A flashlight caught the animal sitting in the grass.
The cane toad moved to flee when boys rushed to it. But it was so big and slow that it was easily caught. Twenty-six cane toads were captured in an hour of hunting.
Cane toads were apparently introduced to Ishigakijima around 1978 from Minami-Daitojima island, more than 700 km away.
Shigeru Nakama, who works for a company in the sugar cane industry in Minami-Daitojima, recalls a visitor from Ishigakijima.
"A person in the sugar-refining business came over one day and captured several cane toads and scooped tadpoles in a pond in order to get them to remove insects damaging sugar canes," Nakama said.
Cane toads can be seen around Ishigakijima throughout the year. They are very active in summer and come out from their habitats at night.
On Aug. 9, the island started a full-fledged campaign to cull the amphibian, with many islanders joining the effort.
Collection boxes were placed at 12 locations for islanders to dispose of their catches.
The first such effort last fall culminated in the capture of 2,582 cane toads in just two weeks. The number totaled about 3,200 in one year.
This summer, 5,097 were caught between Aug. 9 and Aug. 31.
While the eradication campaign is designed to preserve the ecosystem of Ishigakijima, it also has a growing urgency to prevent cane toads from reaching neighboring islands.
Ishigakijima, about 410 km southwest of the prefectural capital of Naha, is a hub for ships traveling on to Taketomijima island, Hatomajima island and other islands in the Yaeyama island chain.
Cane toads could potentially become mixed in with cargo bound for the other islands.
The ministry last year hired Katsube, who has studied amphibians, to lead efforts to cull the creatures.
The island deemed most vulnerable to an explosion in cane toad population is Iriomotejima, a 40-minute trip by boat from Ishigakijima, with which it has a steady flow of people and cargo.
The survival of the Iriomote yamaneko, a critically endangered species, could be further threatened.
Iriomotejima confirmed the presence of a cane toad for the first time in 1986. The amphibian has been sighted almost every year since 2000.
One island where the poisonous toads are welcomed is Minami-Daitojima, a habitat for cane toads since before World War II.
Many islanders say they would be in trouble with more insect pests if not for the cane toad.
Sugar cane cultivation accounts for 90 percent of the island's agricultural produce.
Locust outbreaks are a much greater source of fear for farmers than cane toads.
Records show that a plague of grasshoppers in the early Showa Era (1926-1989) forced islanders to toil day and night for three days to eradicate the insect pest.
In recent years, swarms of locusts have devoured sugar cane crops.
Kazuaki Higashi, an official with expert knowledge of the flora and fauna of the island, says any attempt to stamp out the amphibian could end up harming the ecosystem of the island.
Higashi works at Shima Marugoto Kan, a facility to explain the island's culture and history.
"Three species of the amphibian here were all introduced from elsewhere," he said. "If they were gone, it would give a rise to the number of bugs, destroying the ecosystem that was established in the pioneering days of the island."(IHT/Asahi: September 14,2009)
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