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The cause of the outbreak is unknown, but scientists believe it is always fatal.
“I’m flustered looking for words here,” said Joel Berger, a senior scientist at the Wildlife Conservation Society. “To lose 120,000 animals in two or three weeks is a phenomenal thing.”
Before the end of the Ice Age, saiga lived over a vast range stretching from England to Alaska. After the climate warmed, they continued to thrive on the steppes of Central Asia.
After the fall of the Soviet Union, however, the saiga population fell by more than 95 percent. Poachers were mainly responsible, killing the animals to sell their horns in China for use in traditional medicines.
In 2006, the five nations where saiga still survived — Kazakhstan, Mongolia, Russia, Turkmenistan and Uzbekistan — signed a memorandum of understanding to conserve the species. Anti-poaching measures have helped the population recover from less than 50,000 to about 250,000 before the current die-off.
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Earlier this month, Aline Kuehl-Stenzel, the terrestrial species coordinator of the Convention on the Conservation of Migratory Species of Wild Animals, an environmental treaty overseen by the United Nations, received a report from the Kazakhstan government that hundreds of saiga had suddenly died, including many mothers with nursing calves. The death toll has continued to climb ever since
Many species of grazing mammals suffer periodic die-offs, which can be caused by drought or viruses such as rinderpest. But because the saiga population is so reduced, the current die-off has claimed a huge proportion of the species.
“The scale is absolutely unprecedented,” said Dr. Kuehl-Stenzel.
Recently Richard A. Kock, an expert on wildlife disease at the Royal Veterinary College, and his colleagues went to Kazakhstan to help with the investigation. They examined dead animals, performing necropsies on 15 of them.
The scientists found that once the disease struck a herd, it killed every animal. “It is an extraordinary thing to get one hundred percent mortality,” Dr. Kock said.
The scientists found that the animals were infected with two species of deadly bacteria, Pasteurella and Clostridium. But Dr. Kock is convinced that the bacteria are not the fundamental cause of the die-off.
Both species of bacteria are present in healthy animals, becoming lethal only when the animals grow weak. Dr. Kock also observed that the saiga died so quickly from their infections that they could not have spread the bacteria to other animals.
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Dr. Kock and his colleagues are investigating other factors that may have triggered the die-off, including the possibility of an unknown virus. Dr. Kock said it will take three or four weeks to isolate any agent in the necropsy tissues.
The scientists are also looking at how changes in the environment may have put stress on the saiga. Heavy rainfall this year may have altered the ecology of the steppes, disrupting their food supply, for example.
Central Asia has also experienced heavy chemical pollution over the decades from both factories and farms. “There’s a lot of history there,” said Dr. Kock, who will be examining pollution’s possible role in the die-off.
There has been speculation that the saiga were poisoned by fuel from Kazakhstan’s rocket program, but Dr. Kuehl-Stenzel doubted the hypothesis.
“I haven’t seen any data to support the rocket theory,” she said.
Determining whether the environment contributed to the die-off may take years. “We have some simple stories, but it’s probably more complicated,” said Dr. Kock. “We have to do the science and let the evidence speak.”
On Thursday, the convention issued a statement saying that “the mass die-off has come to an end.” But Dr. Kuehl-Stenzel said on Friday that there were reports that more saiga are dying.
“The die-off may not be over,” she said. “This is unconfirmed, but it fills us with great fear.”
source:www.nytimes.com
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