The discovery of a critically endangered gorilla population in the vast forests of northern Congo is a mammoth 125,000 - double that of previous estimates - should make even the most pessimistic conservation biologist smile.

Western lowlands gorillas.
Western lowlands gorillas.

The numbers of western lowland gorillas living across 47,000 square kilometres of dense forestland were thought to have plummeted from 100,000 to half that number since the 1980s.

Just last year, the threat from the deadly ebola virus and indiscriminate bushmeat hunters prompted the International Union for the Conservation of Nature to add the apes to their critically endangered list.

The results of the census by the Wildlife Conservation Society and local government researchers were announced today at a meeting of the International Primatological Society in Edinburgh, UK.

Researchers undertook intensive fieldwork to count the number of nests - the leafy beds the secretive apes sleep in at night. They found as many as eight individuals per square kilometre, one of the highest gorilla densities every recorded.

Crude estimate

While it seems bizarre that no-one had realised quite how many gorillas there were in the region, says WCS biologist Emma Stokes, who helped coordinate the study. The difficulty in counting the animals is partly to blame, and detecting the nests can be particularly tricky in densely forested areas, as much of this region is.

Not only that, "the old number was a crude estimate", which relied heavily on extrapolation rather than direct observation, she says. Advances in census methodologies, coupled with the enormous scale and significant funding of the survey is what makes this study far more accurate.

The census is particularly positive news in the context of an IUCN evaluation, also presented at the Edinburgh meeting, which warns that 50% of the world's primates are in danger of extinction because their habitats are being destroyed and many animals are illegally hunted as food.

Protection vital

The gorillas do have "an enormous advantage of remoteness", which confers a natural protection from poachers and disease epidemics - some survey areas were 80 km away from roads and villages.

But their location won't protect them forever, cautions Stokes, because most of the gorillas live outside protected areas.

A region called Ntokou-Pikounda, in the middle of the forested area, was given national-park status by the government in 2006, but this was a largely empty gesture since officials did nothing to enforce its protection.

Given that the park is home to 73,000 of the gorillas in the study area, ensuring this region is properly protected should be the first step in saving the apes, says Stokes. This will mean stationing people to catch illegal logging trucks and establishing mobile anti-poaching teams in the area.

Because ebola epidemics can quickly reduce as much as 95% of a population, understanding how the virus is transmitted to the animals, and developing vaccines - as well as clever ways of getting the vaccines to the animals fast - will be crucial to protecting the animals, says Stokes.