Unlike mountain gorillas, which number in the hundreds, the western lowland gorilla population is still large enough and inaccessible enough that conservationists do not know its size with any real accuracy.
What conservationists do know is that ape populations are plummeting, decimated by the combined effects of the Ebola virus, commercial hunting and deforestation. The gorillas' ability to recover remains in question, despite recent research led by the Wildlife Conservation Society.
"Ebola has resulted in dramatic local declines in gorilla populations in Congo and Gabon in the last two decades, with population crashes of more than 95 percent being recorded," said Emma Stokes, a scientist with the Wildlife Conservation Society.
"Given the long life spans and slow reproductive cycles of great apes, recent estimates suggest it may take up to 120 years to recover from population crashes of this magnitude," Stokes said.
Threats To The Species
In 2003, a team of scientists reported in Nature that between 1983 and 2000, the ape population in Gabon declined by more than half as a result of commercial hunting and Ebola hemorrhagic fever. They called for gorillas to be listed immediately as critically endangered — a status that means they are expected to suffer a reduction of at least 80 percent in the next three generations. The scientists projected an 80 percent loss in two generations.
Until that point, commercial hunting was considered the most pressing threat to the gorillas' existence. The expanding logging industry had transformed hunting from primarily a subsistence activity into a widespread commercial enterprise, by opening previously inaccessible forest areas to hunters and by providing an infrastructure to transport the bushmeat long distances, reported the scientists.
Between 2003 and 2004, the Zaire strain of the Ebola virus further ravaged the gorilla populations in Gabon and Congo, making the disease as dire a threat as hunting. Scientists in the Lossi Sanctuary in northwest Congo reported in the journal Science that Ebola killed 5,000 gorillas in their study area alone — 90 to 95 percent of the population.
And while commercial hunting is heaviest near human populations, Ebola's scourge is concentrated in remote areas. Observations of ape carcasses that were not slain by hunters spanned 600 km, from west of Booue to the Nouabale–Ndoki region of northern Congo, and was most severe between Lossi and Odzala National Park, the scientists said.
Scientists are able to estimate losses without knowing entire population numbers because losses are generally recorded by measuring changes in gorilla density or numbers in limited areas.
Critically Endangered
The World Conservation Union classified the western lowland gorilla as "critically endangered" in 2007.
It is the most populous of the gorilla subspecies and currently lives in seven countries across western equatorial Africa. Whereas western mountain gorillas can still be counted in the tens of thousands, the eastern lowland gorilla numbers in the thousands and the mountain and cross-river gorilla populations have shrunk to mere hundreds.
The 125,000 apes newly counted in the Wildlife Conservation Society's survey are an enormous boost for the subspecies' chance of survival and for the efforts of conservationists. But the miraculous finding is not without a shadow.
"Ebola is a localized threat to gorilla populations," said Stokes. "These important gorilla populations of 125,000 individuals are adjacent to areas that are known to have been impacted by Ebola outbreaks in recent years."
Although her team's data show that the virus has not yet reached these populations, she said that working quickly to protect this new found mother lode is paramount.
"Until it can be established that the risks from Ebola and hunting are sufficiently reduced or removed across their range," Stokes said, "then western gorillas will remain critically endangered."
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