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A young Tapanuli orangutan. Fewer than 800 members of the species remain in a fragmented 1200-square-kilometer area in North Sumatra.

Andrew Walmsley/Minden Pictures

Dam threatening world’s rarest great ape faces delays

A threat to the world’s rarest ape has receded. After an international pressure campaign, the Bank of China this summer abandoned its plan to finance the Batang Toru hydropower project, which would further reduce the tiny habitat of the Tapanuli orangutan (Pongo tapanuliensis), officially recognized as a separate species only 3 years ago. In the wake of the move, scientists and conservationists are calling for a new, independent scientific assessment of the population and an effort to save the species, which has frizzier, lighter colored hair than its relatives.

The bank did not respond to requests for comment from Science, and the company building the project, P.T. North Sumatra Hydro Energy (NSHE), declined to confirm the decision. A spokesperson said the bank is “only one of several lenders” and that construction, already underway, will proceed as planned. But Ikhsan Asaad, megaproject director at Indonesia’s National Electricity Company, the owner of the project, told local media in June that the bank’s withdrawal—which he said was because of environmental issues and the COVID-19 pandemic—might cause the project to be postponed to 2025. The World Wildlife Fund China praised the bank’s decision in a statement in early September.

Only 767 Tapanuli orangutans remain in an already fragmented area of 1200 square kilometers (km2), according to the International Union for Conservation of Nature (IUCN). The hydropower plant, meant to provide a sustainable electricity supply to 400,000 households in North Sumatra, will be built in the ape’s habitat, but NSHE spokesperson Firman Taufick says, “The Tapanuli orangutan will be safeguarded.”

The project’s footprint will be relatively small, Taufick says, because it is a run-of-the-river plant, which does not require a large reservoir. A study published in February led by Didik Prasetyo of the Center for Sustainable Energy and Resource Management at the University of Indonesia, says only 3.4 km2 of forest has been cleared for the project and that more than half of that “will be subject to ecological restoration.” The study, which was funded by NSHE, found that “at least six” orangutans were living in the project area.

But the report doesn’t discuss the core issue, says Erik Meijaard, a member of the IUCN group and director of Borneo Futures, a consultancy company based in Brunei. The project sits at the crossroads of three subpopulations of the Tapanuli orangutan and is likely to separate them permanently, which increases the risk of extinction. “It is not about how much habitat has been lost,” Meijaard says, “but more about the vital role [the area] plays in keeping populations connected.” (He and others also worry the construction of roads for the project will attract additional development.)

Primatologist Wanda Kuswanda of the government’s Natural Resource Conservation Agency thinks the dam will have little impact on the orangutans, arguing that those connections were lost well before the project started. The two main populations, named the east block and the west block, are separated by the Trans-Sumatra Highway and the Batang Toru river. That river also separates the west block from a third, smaller population, named the west-south block, which sits in South Tapanuli district, the area where the hydropower project is located. A few trees with overhanging branches still act as natural bridges, Kuswanda says, but the rise of smallholder plantations on the riverbanks since 2000 has made orangutan crossings rare.

Instead, the main threat to the Tapanuli orangutan today is an increasing number of conflicts with local people, Kuswanda says. A study he and his colleagues published in the journal Biodiversitas in July showed 85 orangutans live outside protected areas in South Tapanuli, roaming on community land and eating locally grown crops such as durian and petai beans. People often try to scare them off by “using fires, shouting while throwing sticks, and even gunshots,” Kuswanda wrote in the paper.

Kuswanda says his study is independent: “NSHE nor the IUCN pays me for a living. And I am presenting the data the way it is.” The Indonesian Ministry of Environment and Forestry (KLHK) has said it is carefully monitoring the project’s impact on orangutans and that the population is not at risk of going extinct. KLHK has also said it will develop “corridors” connecting the subpopulations, together with NSHE and PanEco, a Swiss conservation group that initially opposed the project but now is helping mitigate its impact.

Primatologist Serge Wich of Liverpool John Moores University, vice chair of IUCN’s Primate Specialist Group, is critical of both studies for not making their raw data—such as nest locations and human-orangutan conflicts—publicly available in the A.P.E.S. database.

Meijaard says the two studies don’t give scientists a full understanding of the threats to the orangutan. “It would require a much broader study of population size and trend, dispersal rates between subpopulations, updated viability studies, and accurate quantification of annual losses of animals,” he says.

A third study by Wich, Meijaard, and others, published as a preprint in September, shows how much Tapanuli orangutan habitat has already been lost. Historical records—including natural history books and newspaper reports from the colonial era—show the species once roamed as far away as South Sumatra, 1050 kilometers from its current habitat. The authors estimate the species has held on to just 2.7% of the range it had in 1890, and 5% of its territory in 1940. The study shows “the species is extremely sensitive to the combined effects of hunting and habitat fragmentation, and that populations can go extinct very quickly and easily,” Meijaard says.

“We trust that the Indonesian government recognizes the urgency of this issue,” he says, “and that it will work with the various national and international experts to prevent what could otherwise be the first great ape extinction in modern times.”