PERSPECTIVES AND NOTES
The Tapanuli orangutan: Status, threats, and steps for improved
Serge A. Wich
| Gabriella Fredriksson
| Graham Usher
| Hjalmar S. Kühl
Matthew G. Nowak
School of Natural Sciences and Psychology, Liverpool John Moores
University, Liverpool, UK
Institute for Biodiversity and Ecosystem Dynamics, University of
Amsterdam, Amsterdam, the Netherlands
Conservation Division, The PanEco Foundation - Sumatran Orangutan
Conservation Programme, Berg am Irchel, Switzerland
Department of Primatology, Max Planck Institute for Evolutionary
Anthropology, Leipzig, Germany
Sustainability and Complexity in Ape Habitat Group, German Centre for
Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Leipzig,
Department of Anthropology, Southern Illinois University, Carbondale,
Serge A. Wich, School of Natural Sciences and Psychology, James Parsons Building, Byrom street, L33AF, Liverpool, UK.
KEYWORDS: Batang Toru, hydrodam, Tapanuli orangutan
Ever since the Tapanuli orangutan (Pongo tapanuliensis)
was described two years ago (Nater et al., 2017) it has fre-
quently been in the news for two primary reasons. First,
because of the excitement generated by the discovery of the
first new extant great ape species since 1929. Second,
because of the immediate threat posed to the new species by
the development of a hydrodam to generate electricity
(Sloan, Supriatna, Campbell, Alamgir, & Laurance, 2018).
As the species has only been described recently there is no
paper that summarizes its status and threats even though
some of that information is available from a previous study
where this species was still considered a population of the
Sumatran orangutan (Pongo abelii) (Wich et al., 2016). In
this letter, we aim to remedy this gap by providing a succinct
overview of the status of and threats to the Tapanuli orangu-
tan, as well as by identifying key steps toward improved
conservation. This is particularly relevant as there is a need
to be able to determine the impact of the hydroelectric dam
development which is best achieved from a clear baseline.
As with the other two orangutan species, the Tapanuli
orangutan is considered to be Critically Endangered by the
International Union for Conservation of Nature (IUCN)
(Nowak, Rianti, Wich, Meijaard, & Fredriksson, 2017). The
species is only found in the forests of the Batang Toru Eco-
system in the province of North Sumatra, Indonesia
(Figure 1). Based on extensive survey work from 2000 to
2012 it has been determined that the total extent of its distri-
bution covers 1,023 km
(Wich et al., 2016). It is found in
three main forest blocks with a total of 767 individuals (95%
confidence intervals [CI] [231–1,597]): the west block
which houses 581 individuals (95%CI [180–1,201] [sum of
533, 42, and 6 in Figure 1]), the east block with 162 individ-
uals (95% CI [46–341]), and the Sibual-buali Reserve with
24 individuals (95% CI [6–53], based on (Wich et al., 2016),
with possibly small populations to the north and/or in the
Lubuk Raya Reserve). Of this distribution, roughly 85% is
under some form of protection status, but 15% is land for
other uses (Nowak et al., 2017). The west block and the
Received: 8 February 2019 Accepted: 27 March 2019
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original
work is properly cited.
© 2019 The Authors. Conservation Science and Practice published by Wiley Periodicals, Inc. on behalf of Society for Conservation Biology
Conservation Science and Practice. 2019;1:e33. wileyonlinelibrary.com/journal/csp2 1of4
Sibual-buali Reserve are still moderately connected and
orangutan dispersal is expected to occur between those areas
based on the locations where nests have been found during
surveys (Figure 1). It is less clear if orangutans can still
move between the west and east block because of the pro-
vincial road from Tarutung to Padangsidempuan separating
these blocks as well as the Batang Toru River.
There are several threats to the Tapanuli orangutan.
Between 1985 and 2007, 43.3% of the forests in the province
of North Sumatra (where the Tapanuli orangutan occurs)
have been lost (Wich, Riswan, Jenson, Refisch, &
Nellemann, 2011). Annual deforestation rates were particu-
larly high from 1985 to 1990 (4.2%), decreased from 1990
to 2000 (1.2%), and then increased again from 2000 to
2008/2009 (2.3%). Particularly recent losses of peat swamp
areas on the coast where the species had been found in the
past (Wich et al., 2003) have led to a reduction of forest for
the Tapanuli orangutan as well as the slower but steady for-
est loss that occurs around all three blocks. During
1990-2009, annual forest loss for the area in which the
Tapanuli orangutan occurs was calculated as 0.11%, with a
range of <0.01–0.84% (Wich et al., 2011). This is lower
than the overall annual forest loss for North Sumatra due to
the Tapanuli orangutan occurring in more mountainous areas
which have lower deforestation rates than areas at lower ele-
vations. The other main threat is killing of orangutans. This
occurs in two circumstances. First, orangutan hunting still
occurs in the area (Wich et al., 2012). Even though hunters
do not seem to go into the forest to specifically hunt for
orangutans, they do opportunistically hunt/kill them for food
when encountered (Wich et al., 2012). Second, orangutans
that venture into community plantations have been killed as
a result of human-orangutan conflict (Nater et al., 2017). As
orangutans are long-lived and have slow reproductive rates,
even low levels of extrinsic mortality (i.e., >1% per year,
which in this case is just a few individuals) represent a major
threat to the long-term growth, stability, and persistence of
the small-sized Tapanuli orangutan populations (Marshall et
In addition to these threats there is a hydroelectric dam
with associated infrastructure planned in the area (Sloan
et al., 2018). The area of influence of the dam is planned in
an area with the highest Tapanuli orangutan densities and
covers 5.5% (42 individuals, 95%CI [14–84]) of the total
FIGURE 1 Map showing the distribution of the Tapanuli orangutans, their population numbers and threats. The 95% confidence intervals (CI)
for the various areas are: West block: 164–105, East block: 46–341, Hydro AoI: 14–84, Corridor: 2–12, Sibual-buali: 6–53
2of4 WICH ET AL.
Tapanuli orangutan population (Wich et al., 2016). Orangu-
tans in this area and surroundings will be negatively impacted
through habitat degradation and loss. This is of particular con-
cern for orangutan females because they are philopatric and
tend not to move when they lose parts of their home range
(van Schaik, 2004) and risk starvation or being killed when
this occurs. Such home range loss and subsequent dispersal
can also lead to compression of orangutans in adjacent areas
and inflated densities past the carrying capacity and hence
lead to food shortages and future reductions in density
(Husson, personal communication, January 15, 2019). If parts
of their home range are lost, orangutans in disturbed areas will
have to use the remaining parts of their own home range more
intensively than before, which can also lead to social tension
between females (Ashbury et al., 2015).
Additionally, the hydroelectric dam and its associated
infrastructure will separate the Sibual-buali Reserve from the
west block and will also impact the options for reconnecting
the east and west block. Over 20 km of road and 14 km of
electricity transmission lines through Tapanuli orangutan
habitat are planned, and at least 3 million m3 of excavated
spoil is planned to be dumped in orangutan habitat
(Comanditaire Venotschap (CV) Global Inter System, 2014,
2016). Furthermore, it is well-established that infrastructure
development, especially roads, can facilitate human access
into previously inaccessible areas, eventually leading to
additional and often unrestricted levels of habitat degrada-
tion and loss, hunting, and/or human-animal conflict
(Laurance, 2015; Laurance & Arrea, 2017; van der Ree,
Smith, & Grilo, 2015).
Taken together, the hydroelectric project will drive the
Sibual-buali and Sitandiang corridor population (30 individ-
uals, 95% CI [8–65]) and east block population (162 individ-
uals) to a status of nonviable, which is defined here as a
population with 0% probability of extinction and >90%
retention of genetic diversity for a minimum of 1,000 years
(Singleton et al., 2004; Marshall et al., 2009). Following the
results of the 2004 orangutan Population and Habitat Viabil-
ity Assessment (PHVA) workshop, a population of >500
individuals is considered viable using this definition (Single-
ton et al., 2004). This will leave the west block as the last
remaining viable Tapanuli orangutan population. But given
the current and projected threats of habitat degradation and
loss, hunting, human-orangutan conflict, an expanding
goldmine, and a neutralized logging concession in the area
(GoNSP, 2017; MoEF, 2017; MoF, 2014), this is an
extremely risky scenario and should therefore be avoided at
all costs, because these threats could drive this population to
nonviable status within as few as 1–2 generations.
In conclusion, the Tapanuli orangutan was the latest
extant great ape to be discovered, but given its extremely
small population numbers and current and projected threats,
it might well be the first one to go extinct. This would con-
travene the Indonesian Law Regarding the Conservation of
Biological Resources and Ecosystems (Law No. 5/1990), as
well as the Aichi targets to which the Indonesian govern-
ment has committed (Darajati et al., 2016; PoRI, 1990). As
such, it is imperative that the Government of Indonesia takes
some bold steps to secure its future, of which the most
important short-term ones are: (a) to halt the hydroelectric
dam development; (b) change the land use status of the
unprotected 15% of the area where the Tapanuli orangutan
occurs to a protected status; and (c) establish a corridor
between the west and east block and improve the corridor
between the west block and Sibual-buali Reserve. In addi-
tion, the ongoing hunting and small-scale deforestation need
to be halted through serious enforcement of Indonesia's reg-
ulations concerning protected species.
CONFLICT OF INTEREST
The authors declare no potential conflict of interest.
S.A.W., G.F., G.U., and M.G.N. conceived the paper,
S.A.W., G.U., M.G.N., and H.S.K. conducted the analyses,
S.A.W., G.F., G.U., H.S.K., and M.G.N. wrote the paper.
No ethics approval was needed for this study. All data are
available on request from the authors.
Serge A. Wich https://orcid.org/0000-0003-3954-5174
Ashbury, A. M., Posa, M. R. C., Dunkel, L. P., Spillmann, B.,
Atmoko, S. S. U., van Schaik, C. P., & van Noordwijk, M. A.
(2015). Why do orangutans leave the trees? Terrestrial behavior
among wild Bornean orangutans (Pongo pygmaeus wurmbii)at
Tuanan, Central Kalimantan. American Journal of Primatology,77,
Comanditaire Venotschap (CV) Global Inter System. (2014). ANDAL:
Rencana Pembangunan Pembangkit Listrik Tenaga Air (PLTA)
Batangtoru Kapasitas 500 MW Dan Jaringan Transmisi 275 KV
Dari PLTA Batang toru Sampai Desa Parsalakan Kec. Angkola
Barat Kab. Tapanuli Selatan Prov. Sumatera Utara. Medan,
Republic of Indonesia: Perseroan Terbatas (PT) North Sumatera
Comanditaire Venotschap (CV) Global Inter System. (2016). Adendum
ANDAL, RKL-RPL: Rencana Kegiatan Pembangunan Pembangkit
Listrik Tenaga Air (PLTA) Batang Toru Dari Kapasitas 500 MW
Menjadi 510 MW (4 x 127.5 MW) Dan Perubahan Lokasi Quarry
Di Kabupaten Tapanuli Selatan - Provinsi Sumatera Utara.
WICH ET AL.3of4
Medan, Republic of Indonesia: Perseroan Terbatas (PT) North
Sumatera Hydro Energy.
Darajati, W., Pratiwi, S., Herwinda, E., Radiansyah, A. D., Nalang, V.
S., Nooryanto, B., …Hakim, F. (2016). Indonesian biodiversity
strategy and action plan (IBSAP) 2015-2020. Jakarta, Republic of
Indonesia: Ministry of National Development Planning / National
Development Planning Agency of the Republic of Indonesia.
GoNSP. (2017). Peraturan Daerah Provinsi Sumatera Utara, Nomor 2
Tahun 2017,Tentang rencana tata ruang wilayah Provinsi Sum-
atera Utara tahun 2017-2037. Medan, Republic of Indonesia: Gov-
ernor of North Sumatra Province of the Republic of Indonesia.
Laurance, W. F. (2015). Bad roads, good roads. In R. van der Ree, D.
J. Smith, & C. Grilo (Eds.), Handbook of road ecology (pp. 10–15).
New York, NY: John Wiley & Sons.
Laurance, W. F., & Arrea, I. B. (2017). Roads to riches or ruin? Sci-
Marshall, A. J., Lacy, R., Ancrenaz, M., Onnie, B., Husson, S. J.,
Leighton, M., …Wich, S. A. (2009). Orangutan population biol-
ogy, life history, and conservation. In S. A. Wich, S. S. Utami
Atmoko, T. Mitra Setia, & C. P. van Schaik (Eds.), Orangutans:
Geographic variation in behavioral ecology and conservation
(pp. 311–326). New York, NY: Oxford University Press.
MoEF. (2017). Surat Keputusan Menteri Lingkungan Hidup dan
Kehutanan Republik Indonesia, Nomor: SK.1076/MENLHK-
PKTL/KUH/PLA.2/3/2017, Tentang Peta Perkembangan Pen-
gukuhan Kawasan Hutan Provinsi Sumatera Utara Sampai Den-
gan Tahun 2016. Jakarta, Republic of Indonesia: Ministry of
Environment and Forestry of the Republic of Indonesia.
MoF. (2014). Surat Keputusan Menteri Kehutanan Republik Indonesia,
Nomor: SK.579/MENHUT-II/2014, Tentang Kawasan Hutan Pro-
vinsi Sumatera Utara. Jakarta, Republic of Indonesia: Ministry of
Forestry of the Republic of Indonesia.
Nater, A., Mattle-Greminger, M. P., Nurcahyo, A., Nowak, M. G., De
Manuel, M., Desai, T., …Krützen, M. (2017). Morphometric,
behavioral, and genomic evidence for a new orangutan species.
Current Biology,27(22), 3487–3498, e3410.
Nowak, M. G., Rienzi, P., Wich, S. A., Meijaard, E., & Fredriksson, G.
(2017). The IUCN red list of threatened species 2017.
Pongo tapanuliensis. https://doi.org/10.2305/IUCN.UK.2017-3.
PoRI. (1990). Undang-Undang Republik Indonesia, Nomor 5 Tahun 1990,
Tentang Konservasi Sumber Daya Alam Hayati Dan Ekosistemya.
Jakarta, Republic of Indonesia: President of the Republic of Indonesia.
Singleton, I., Wich, S., Husson, S., Stephens, S., Utami Atmoko, S. S.,
Leighton, M., …Byers, O. (2004). Orangutan population and hab-
itat viability assessment: Final report. Apple Valley, MN: IUCN/-
SSC Conservation Breeding Specialist Group.
Sloan, S., Supriatna, J., Campbell, M. J., Alamgir, M., &
Laurance, W. F. (2018). Newly discovered orangutan species
requires urgent habitat protection. Current Biology,28,R650–R651.
van der Ree, R., Smith, D. J., & Grilo, C. (2015). The ecological effects of
linear infrastructure and traffic: Challenges and opportunities of rapid
global growth. In R. van der Ree, D. J. Smith, & C. Grilo (Eds.), Hand-
book of road ecology (pp. 1–9). New York, NY: John Wiley & Sons.
van Schaik, C. P. (2004). Among orangutans: Red apes and the rise of
human culture. Cambridge, MA: Harvard University Press.
Wich, S. A., Fredriksson, G. M., Usher, G., Peters, H. H., Priatna, D.,
Basalamah, F., …Kühl, H. (2012). Hunting of Sumatran orang-
utans and its importance in determining distribution and density.
Biological Conservation,146, 163–169.
Wich, S. A., Riswan, J., Jensom, J., Refisch, J., & Nellemann, C.
(2011). Orangutans and the economics of sustainable forest man-
agement in Sumatra. United Nations Environment Programme
(UNEP). Birkeland, Norway: Birkeland Trykkeri AS.
Wich, S. A., Singleton, I., Nowak, M. G., Utami Atmoko, S. S.,
Nisam, G., Arif, M. S., …Kühl, H. S. (2016). Land-cover changes
predict steep declines for the Sumatran orangutan (Pongo abelii).
Science Advances,2, e1500789.
Wich, S. A., Singleton, I., Utami-Atmoko, S. S., Geurts, M. L.,
Rijksen, H. D., & van Schaik, C. P. (2003). The status of the Suma-
tran orang-utan Pongo abelii: An update. Oryx,37,49–54.
How to cite this article: Wich SA, Fredriksson G,
Usher G, Kühl HS, Nowak MG. The Tapanuli
orangutan: Status, threats, and steps for improved
conservation. Conservation Science and Practice.
4of4 WICH ET AL.