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The Sumatran orangutan (''Pongo abelii'') is one of the three species of orangutans and is native to the island of Sumatra, Indonesia. The most recent population estimate for the Sumatran orangutan stands at 13,846 individuals, inhabiting a total forest area of 16,775 km² (Wich et al. 2016). Considering only populations with over 250 individuals (deemed potentially viable in the long term) leaves 13,587 individuals. The majority, 95.0%, reside in the Leuser Ecosystem, while others are found in the Sidiangkat and Pakpak. This 2016 estimate surpasses the previous one of around 6,600 individuals, owing to improved survey techniques and expanded coverage rather than an actual increase. Notably, overall numbers continue to decline significantly (Singleton et al. 2023).

The Sumatran orangutan (''Pongo abelii'') is one of the three species of orangutans and is native to the island of Sumatra, Indonesia. The most recent population estimate for the Sumatran orangutan stands at 13,846 individuals, inhabiting a total forest area of 16,775 km² (Wich et al. 2016). Considering only populations with over 250 individuals (deemed potentially viable in the long term) leaves 13,587 individuals. The majority, 95.0%, reside in the Leuser Ecosystem, while others are found in the Sidiangkat and Pakpak. This 2016 estimate surpasses the previous one of around 6,600 individuals, owing to improved survey techniques and expanded coverage rather than an actual increase. Notably, overall numbers continue to decline significantly (Singleton et al. 2023).

Given the discovery of orangutans at altitudes up to 1,500 m asl in various areas, connectivity among subpopulations in the mountainous Leuser Ecosystem is likely better than previously believed (Wich et al. 2008). However, recent studies indicate genetic differentiation between subpopulations, partly attributed to geographic barriers like rivers and high mountain ridges, even within the Leuser Ecosystem (Nater et al. 2013).

Given the discovery of orangutans at altitudes up to 1,500 m asl in various areas, connectivity among subpopulations in the mountainous Leuser Ecosystem is likely better than previously believed (Wich et al. 2008). However, recent studies indicate genetic differentiation between subpopulations, partly attributed to geographic barriers like rivers and high mountain ridges, even within the Leuser Ecosystem (Nater et al. 2013).

Apart from wild populations, two new Sumatran orangutan populations are emerging through the reintroduction of confiscated illegal pets—one around Bukit Tigapuluh National Park (Jambi and Riau provinces) and another around Jantho Pine Forest Nature Reserve in northern Aceh, with over 260 individuals reintroduced. The aim is to establish genetically-viable, self-sustaining wild populations as a safety net (Singleton et al. 2023).

Apart from wild populations, two new Sumatran orangutan populations are emerging through the reintroduction of confiscated illegal pets—one around Bukit Tigapuluh National Park (Jambi and Riau provinces) and another around Jantho Pine Forest Nature Reserve in northern Aceh, with over 260 individuals reintroduced. The aim is to establish genetically-viable, self-sustaining wild populations as a safety net (Singleton et al. 2023).

'''Threats'''<br>

'''Threats'''<br>

The survival of the Sumatran orangutan faces serious threats primarily due to habitat loss and fragmentation caused by large-scale clearing of forests for oil-palm plantations and logging activities (Wich et al. 2008, 2011, 2016). The creation of new roads, often for illegal settlements and agriculture, poses additional risks by fragmenting populations and providing access to wildlife poachers. Industrial plantations force orangutans to seek refuge in remaining forest patches, leading to long-term challenges like malnutrition and starvation due to limited resources. The illegal pet trade and deliberate killings further jeopardize their existence, with human-wildlife conflicts arising from incidents like crop raiding (Wich et al. 2012).

The survival of the Sumatran orangutan faces serious threats primarily due to habitat loss and fragmentation caused by large-scale clearing of forests for oil-palm plantations and logging activities (Wich et al. 2008, 2011, 2016). The creation of new roads, often for illegal settlements and agriculture, poses additional risks by fragmenting populations and providing access to wildlife poachers. Industrial plantations force orangutans to seek refuge in remaining forest patches, leading to long-term challenges like malnutrition and starvation due to limited resources. The illegal pet trade and deliberate killings further jeopardize their existence, with human-wildlife conflicts arising from incidents like crop raiding (Wich et al. 2012).

The most significant current threat stems from the government-ratified spatial land-use plan in Aceh Province, initiated in 2013. Despite obligations for Leuser Ecosystem conservation under Aceh's autonomy law, the plan neglects its existence, allowing the designation of vast orangutan habitats for plantations, timber, and mining concessions. Legal challenges seek to replace this plan with one complying with laws and providing proper protection for the Leuser Ecosystem. Until then, the 2013 Aceh plan legitimizes illegal roads, exacerbating fragmentation, hunting, and encroachment, posing severe risks to Sumatran orangutan populations (Singleton et al. 2023).

The most significant current threat stems from the government-ratified spatial land-use plan in Aceh Province, initiated in 2013. Despite obligations for Leuser Ecosystem conservation under Aceh's autonomy law, the plan neglects its existence, allowing the designation of vast orangutan habitats for plantations, timber, and mining concessions. Legal challenges seek to replace this plan with one complying with laws and providing proper protection for the Leuser Ecosystem. Until then, the 2013 Aceh plan legitimizes illegal roads, exacerbating fragmentation, hunting, and encroachment, posing severe risks to Sumatran orangutan populations (Singleton et al. 2023).

'''Conservation'''<br>

'''Conservation'''<br>

Wich, S. A., Singleton, I., Nowak, M. G., Utami Atmoko, S. S., Nisam, G., Arif, S. M., ... & Kühl, H. S. (2016). Land-cover changes predict steep declines for the Sumatran orangutan (Pongo abelii). Science advances, 2(3), e1500789. <br>

Wich, S. A., Singleton, I., Nowak, M. G., Utami Atmoko, S. S., Nisam, G., Arif, S. M., ... & Kühl, H. S. (2016). Land-cover changes predict steep declines for the Sumatran orangutan (Pongo abelii). Science advances, 2(3), e1500789. <br>