Can a new plan to relocate the Tasmanian devil save the species?
If you could trade stock in species, now might be the time to sell TSMD: Tasmanian devil. In the past decade, a grotesque cancer has rippled through the island population, killing 90 percent of devils in some areas. Wildlife scientists—baffled by the mysterious disease that spreads only through biting—can't diagnose infected devils until tumors erupt on their faces. Invasive red foxes, which appear to have migrated to Tasmania, could devour the remaining marsupials as the cartoon devil Taz devoured anything in his path.
The latest plan to salvage the devils calls for transplanting hundreds of them to several nearby islands, starting with Maria, a national park off the southwest coast of Tasmania. "We have virtually no other short- to medium-term options available," says wildlife researcher Hamish McCallum of the University of Tasmania. "If we want to ensure free-ranging devil populations that are disease free, putting them on offshore islands is the only alternative we've got."
The proposal, which state and federal officials could decide on by the end of June, is peppered with contention. Some fear the devils might dine on the endangered species—the forty-spotted pardalote and swift parrot, for instance—that live on Maria (pronounced mah-RYE-uh). Others worry that the inevitable increase in dead kangaroos will alarm the campers who frequent the island.
These problems, however, seem minor to experts. Each endangered species on Maria exists in areas of Tasmania where devils thrived before the cancer. And every year hundreds of kangaroos—which, ironically, were moved to Maria in the late 1960s as a potential food supply for another failing species, the now-extinct Tasmanian tiger—are hunted off the island. The devils might simply make this dirty work more visible.
But Maria on its own could not house enough devils to recreate a significant population, and that's where some feel the plan swells in complexity. "To have substantial numbers we'll have to have four or five islands," says Nick Mooney, a biologist with the Tasmanian Department of Primary Industries, Water and Environment (DPIWE). As a national park, Maria has but one owner: the government. Expanding the plan to other islands, however, will require the agreement of land-owning farmers, many of whom fear the devils will eat their livestock. Though the devils will also eat rabbits, wallabies and other native grazers— perhaps even producing a net benefit for the land—negotiations among these many parties could be difficult.
Many wildlife workers believe island relocation suffers from a greater, and more uncontrollable, flaw: the introduction of a diseased devil to one of these clean new locales. That someone would sabotage a signature species might seem absurd (can anyone imagine a person climbing a tree to plant DDT in a bald eagle nest?), but several researchers insist it is a strong threat. "A malicious introduction is real and could easily happen," says Mooney. Even a false tip of such an action could prompt a costly and difficult search. "If you've got the disease in one place," he says, "why risk putting it somewhere else?"
Of course, the risk of moving a diseased devil exists even with a transfer managed by experts. The process of vetting healthy devils is a delicate one. To begin, researchers must pinpoint the dwindling pockets of uninfected Tasmania. They try to stay at least 30 miles away from known diseased areas—a measure of precaution that will become increasingly smaller.
After locating a low-risk area, researchers try to select devils fresh from weaning. At this age, the animals have been in contact with only their mothers. By the time they reach age two or three, however, many devils—especially males—could have engaged in physical interaction with other devils.
From that point, wildlife workers monitor the animals in captivity for ten months after they reach sexual maturity—the timeframe during which tumors typically appear. Such a long observation period, while necessary, carries the risk that the devils might become acclimated to captive living. But the feisty marsupials stand a good shot at re-acquainting themselves to the wild because they learn to scavenge at a young age, says DPIWE's Heather Hesterman. Besides, moving devils into a disease-free area without this incubation period carries the greater danger of contaminating the entire population. "If some have been exposed, it could all be unraveled," says Hesterman. When they are moved to a new location, she says, "it's one-way."
One plan that avoids this path of no return is to erect large, wild enclosures in disease-free areas of Tasmania. But an expansive fence has its own problems, says McCallum. Unlike Australia's dingo fence, where animal prints on the wrong side are conspicuous, a devil barrier would have animal tracks on both sides; a breach wouldn't become apparent until tumors started popping up on the clean side of the fence. "A physical barrier against disease progression needs to be water tight," McCallum says. Removing devils from the wild entirely, an option that requires neither fence nor sea, is hamstrung by the species' poor reproduction rate in captivity.
The lack of unity over any single proposal is, in part, a testimony to the mystery of the facial cancer, and the speed with which it has swept across the island. "It's mind-boggling how rapidly a species can be fiercely affected," says Hesterman, who was studying devil reproduction when the outbreak gained wide notice in the scientific community. The first signs of the cancer, known as "devil facial tumour disease," appeared in 1996. Once a devil is infected, tumors that can be as large as tennis balls balloon from its face. Within a few months, the animal dies of starvation. "There's no sign of resistance," says Hesterman. "There's no sign of recovery."
Typically in nature, when a pathogen ricochets through a population in this manner, the disease begins to disappear once too few animals are left to transmit it. In a 2006 paper in PLoS Biology, McCallum and colleague Menna Jones write that, as far they know, no infection has ever driven its host to extinction. Perhaps because much of the cancer's transmission stems from biting that occurs during sexual interaction, however, this universal failsafe has not held firm. In areas of Tasmania that have been tracked since the first sightings, devil numbers have plunged by 90 percent. "There's no evidence of a decline drop-off," says McCallum. "If the population is dropping by 90 percent in ten years, you won't have much left in 20."
So far, researchers have no vaccine for the rare cancer, which they believe is caused not by a virus but by cells implanted through biting. (Only one other illness, a non-lethal disease in dogs, has similar characteristics.) One popular theory of how the cancer originated—that the pesticide known as 1080 contributed to its emergence—is largely refuted. That chemical is used widely by foresters in Tasmania. In 2005, DPIWE announced plans to test devils for toxins, including 1080. Those tests have yet to be conducted, according to an article in the April 29, 2007, Sunday Tasmanian.
The devil decline could enable the red fox population to establish on Tasmania—a prospect that Mooney sees as a worse threat than the cancer itself. The fox was introduced to Australia in the mid-19th century, and despite public doubts that it has landed on Tasmania, Mooney calls evidence for fox presence there "extremely convincing." Most likely, he says, devil populations suppressed a fox outburst to this point. "You take away devils, it's like taking wolves out of Yellowstone," says Mooney, referring to the disruption caused in the biological chain when gray wolves were removed from the U.S. national park.
If foxes do live on Tasmania, removing them could be extremely expensive, says conservationist Josh Donlan of Cornell University, who is familiar with the devil's plight. When Donlan participated in the removal of goats from the island of Santiago in the Galapagos, he says, it cost $5 million to remove the first 70,000 or so goats, and another million to get rid of the final 1,000. "And Tasmania," he says, "would be starting with the last ones."
Scientists do have another option: relocate the devil to free-range areas in mainland Australia. Of course, then Tasmania would lose jurisdiction over its eponymous species. And would a Tasmanian devil living anywhere but Tasmania be properly named? That question, however touchy, would likely be welcomed if it meant the devil had survived the current scare. "Every 50 devils we put somewhere is 50 devils that would have contracted the disease and died," says Hesterman. "If we leave them in the wild, we know what's going to happen to them."