Indonesia’s deadly flooding was an “extinction-level disturbance” for the world’s rarest great ape, the Tapanuli orangutan, causing catastrophic damage to its habitat and survival prospects, scientists warned on Friday.

Only scientifically classified as a species in 2017, Tapanulis are incredibly rare, with fewer than 800 left in the wild, confined to a small range in part of Indonesia’s Sumatra.

One dead suspected Tapanuli orangutan has already been found in the region, conservationists told AFP.

“The loss of even a single orangutan is a devastating blow to the survival of the species,” said Panut Hadisiswoyo, founder and chair of the Orangutan Information Centre in Indonesia.

Analysis of satellite imagery combined with knowledge of the Tapanuli’s range suggests last month’s flooding, which killed nearly 1,000 people, may also have devastated wildlife in the Batang Toru region.

The scientists focused on the area known as the West Block, the most densely populated of three known Tapanuli habitats, home to an estimated 581 Tapanulis before the disaster.

“We think that between 6 and 11% of orangutans were likely killed,” said Erik Meijaard, a longtime orangutan conservationist.

“Any kind of adult mortality that exceeds 1%, you’re driving the species to extinction, irrespective of how big the population is at the start,” he told AFP.

But Tapanulis have such a small population and range to begin with that they are especially vulnerable, he added.

Satellite imagery shows huge gashes in the mountainous landscape, some of which extend for more than a kilometre and are nearly 100 metres wide, Meijaard said. The tide of mud, trees and water toppling down hillsides would have carried away everything in its path, including other wildlife such as elephants.

David Gaveau, a remote sensing expert and founder of the conservation startup The Tree Map, said he was flabbergasted by the before-and-after comparison of the region.

“I have never seen anything like this before during my 20 years of monitoring deforestation in Indonesia with satellites,” he told AFP.

‘Fragile and sensitive’

The devastation means remaining Tapanulis will be even more vulnerable, with sources of food and shelter now washed away.

Over 9% of the West Block habitat may have been destroyed, the group of scientists estimated.

In a draft paper shared with AFP, they warned the flooding represents an “extinction-level disturbance” for Tapanulis.

Environmentalists have long campaigned against industrial activity in Batang Toru, particularly a hydroelectric dam and goldmine.

The highland homes currently inhabited by tapanulis are not their preferred habitat, but it is where remaining orangutans have been pushed by development elsewhere.

Earlier this month, Indonesia’s government said industrial plantations, hydropower and gold mining in the region had “contributed significantly to the pressure on the environment”. It announced a suspension on operating permits for all projects in the region pending a review.

The government, along with environmentalists, has also said deforestation contributed to the scale of the flooding disaster.

A study published on Thursday also said climate change-linked heavier rainfall and warmer seas, which can turbocharge storms played a role.

The orangutan experts urged an immediate halt to development that will damage the remaining Tapanuli habitat, and an immediate survey of the region.

They also back the expansion of protected areas and work to restore lowland forests.

Hadisiswoyo said the region had become eerily quiet after the landslides.

“This fragile and sensitive habitat in West Block must be fully protected by halting all habitat-damaging development,” he told AFP.