The discovery of a new great ape species is a rare event. Prior to the discovery of the Tapanuli orangutan Pongo tapanuliensis in Sumatra in 2017, the last great ape described was the bonobo Pan paniscus, in 1929. Ironically, immediately after its description the Tapanuli orangutan was categorized as Critically Endangered on the IUCN Red List. A recent study suggested that the range of the Tapanuli orangutan has declined by more than 95% in the past 130 years (Meijaard et al., 2020, bioRxiv , 2020.08.11.246058). Saving the rarest great ape in the world requires avoiding all further losses.

Approximately 800 Tapanuli orangutans remain, in three forest blocks. These blocks remain ecologically connected but the development of a hydroelectric project threatens to separate the populations. A goldmine and small-scale farming have previously resulted in loss of forest, and orangutans are being injured or killed by local people. Despite this, the Indonesian Minister of Environment and Forestry has recently declared there is no possibility that the species will go extinct (Anon., 2020, foresthints.news/minister-evidence-shows-no-possibility-of-orangutan-extinction). The Ministry's optimism is not supported by our analysis of historical records of this orangutan, which indicates that the current remaining range of the Tapanuli orangutan is c. 2.5% of the range the species occupied in the 1890s (Meijaard et al., 2020, bioRxiv , 2020.08.11.246058).

Much of this decline appears to have happened before industrial-scale deforestation for plantation development. We believe this orangutan species disappeared from much of its former range as a result of unsustainable hunting in forest that had been fragmented by land clearing for traditional agriculture.

IUCN population viability assessments indicate that an annual offtake of more than 1% of the adult population in suboptimal habitats would drive any population of this slowly reproducing great ape to extinction. Current losses are probably higher. Contrary to statements by the Minister of Environment and Forestry, we believe there is a high possibility that the species will soon go extinct unless we prevent further habitat loss and fragmentation, and ensure zero offtake.

Preventing the first potential extinction of a great ape species in recent history requires development and effective implementation of a detailed conservation action plan that applies the best science available. Such a plan will need to be endorsed by the various national and international parties involved in the area, including the Indonesian government, IUCN, funding bodies and industry.