Scientists find more gorillas in West Africa than they expected - but also warn of a rapid decline

A study has found there could be more gorillas and chimps in West Africa than scientists previously thought.

But it has revealed there is a dark side to the seemingly good news.

While the number of the endangered primates could be more than double previous estimates, it is also declining at an alarmingly rapid rate.

In a first-of-its-kind study, researchers spent a decade in a vast 190,000km2 area of forest, counting lowland gorillas, chimpanzees, and their nests.

It guessed that the 2013 population of gorillas was around 362,000.

This is far more than the previous 150,000-250,000 estimate by the International Union for the Conservation of Nature.

But it is also believed to be 19% less than eight years ago. Then, some 450,000 lived in the forested region of West Africa where such primates are native, according to the team's estimates.

The study's author Fiona Maisels said humans hunting gorillas for food and forest loss could be to blame for the present and future decline of the animals.

Her findings indicate that 80% or more of gorillas will be gone by the end of the century.

Primate expert Paul Garber, who was not involved in the study but praised it, said the losses are likely to have accelerated in the five years since the 2013 count.

"That is a doomsday scenario, and we need to reverse this immediately," he said.

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The study, which spanned an area in Angola, Central African Republic, Equatorial Guinea, Republic of Congo and Gabon, relied on researchers walking about 1.2 miles a day while they looked up, down and sideways to find primates.

Running physical checks in about one quarter of the forest and using computer simulations to account for the rest of the area, they discovered about 20,000 nests - something nobody else had done before, according to Ms Maisels.

The team found around 129,000 chimpanzees as well as hundreds of thousands of gorillas.

While the sample size meant it was not possible to account for a change in the chimp numbers, the team behind the research suspect there has been a decline.

While at least two external scientists say the study is "important", however, it has not been universally praised.

Volker Sommer at University College London said the method of counting nests couldn't be trusted, as it is difficult to tell if they are used in the day or night, if at all.

Adding a computer modelling approach took the "questionable approach" to "new heights", he argued.