The animal favors lowland coastal areas, and much of its habitat runs from the northern to the southeastern part of the island.
But this same region is also home to most of the island's 2,318 human residents.
Izawa said she has no doubts about the most serious threat to the cat's survival: the destruction and fragmentation of its habitat by humans.
People first settled on the island shortly after World War II. Over the last decade the human population has increased by a fifth, while the number of tourists has almost tripled since 1990 to current counts of more than 350,000 visitors a year.
Although Iriomote Jima only has a single main road, that highway runs along the northern coast—straight through the nocturnal feline's habitat.
Forty-one roadkill deaths have been recorded since 1978, most of which happen at night, when the cat hunts.
To make the road safer for the animals, part of it has been designated an "eco-road," with warning signs for drivers and no less than 80 special underpasses meant for the cats to use when crossing.
Since 1995 the Iriomote Wildlife Conservation Center has operated a clinic on the island to look after ill and injured cats. To date 12 cats have been taken in and 4 successfully released back into the wild.
The center also tries to safeguard the cat's varied prey.
At the top of the island food chain, the Iriomote cat eats everything from small mammals to birds, lizards, snakes, fruit bats, crickets, and crabs. And unusually for a cat, it also hunts frogs.
That is why scientists are deeply concerned about the risk from chytrid fungus, a deadly frog disease first reported in Japan near Tokyo late last year.
(Related news: "'Frog Hotel' to Shelter Panama Species From Lethal Fungus" [November 2, 2006].)
If the fungus reaches the island, it could have a catastrophic effect on the frog population with correspondingly severe consequences for the Iriomote cat.
Conservationists have laid out disinfectant mats in the island's ports, and a poster and flier campaign is underway to warn residents and visitors of the danger.
The wildlife center is also working to keep out poisonous cane toads, an invasive foreign species that has already reached nearby islands in the Ryukyus.
But the Iriomote cat is still on the decline, and there is no end in sight to the problem of habitat destruction.
Despite opposition from conservationists, a new hotel with room for 423 guests was built and opened in July 2004.
"In the present situation we are not able to do much to limit the increase and are concerned the island will be overexploited," said Maki Okamura, a scientist at the Iriomote Wildlife Conservation Center.
Iriomote is in Japan's poorest region, and many islanders are keen to increase tourism as well as bolster local agriculture.
"The most difficult and important thing is gaining the understanding of the islanders on the need to protect the cat," Okamura said.
"At times the island's development and the cat's protection are directly opposed."
Extending reserves is one option, Izawa of the University of the Ryukyus said. But, she noted, the cat already shares much of its main habitat with islanders, tourists, and vehicles.
"Reserves are not the solution for all problems. We need some regulation or management by government for the development for tourism."
Both Okamura and Izawa stress that it is still too early to think about captive breeding, saying that the first priority should be efforts to protect the cat in the wild.
"Hopefully," Okamura said, "the reclassification to critically endangered will help to increase awareness that the cat is facing extinction."
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