Western Lowland Gorilla

There are two species of gorilla, the western gorilla (Gorilla gorilla) and the eastern gorilla (Gorilla beringei). The western gorilla consists of two recognized subspecies: the western lowland gorilla (Gorilla gorilla gorilla) and the Cross River gorilla (Gorilla gorilla diehli). The western lowland gorilla, which comprises about 99% of all gorillas, is classified as Critically Endangered according to the IUCN Red List of Threatened Species (Maisels et al. 2018), meaning that it is considered to be facing an extremely high risk of extinction in the wild.

Western lowland gorillas are found throughout the forests of Western Equatorial Africa in Gabon and Republic of the Congo, southwestern Central African Republic (CAR), Cameroon south of the Sanaga River, mainland Equatorial Guinea and the Cabinda province of Angola (Maisels et al. 2018). They appear to be most numerous in Marantaceae and swamp forests.

The most recent estimate of western lowland gorillas was about 361,900 in 2013, with approximately 60% living in the Republic of the Congo, 27% in Gabon, 10% in Cameroon and the rest in CAR, Cabinda, and Equatorial Guinea (Strindberg et al. 2018). Their population is declining at about 2.7% annually, due to the threats outlined below (Strindberg et al. 2018).

Threats

Two main threats to western lowland gorillas are consistent across the western equatorial region: poaching and disease (particularly Ebola virus disease). Poaching is hugely exacerbated by the creation of logging roads (which facilitate both entry of poachers and munitions into the forest and the export of bushmeat out of it) (IUCN 2014) and, indeed, gorilla density is very well predicted by proximity to unprotected roads and by the absence of guards (Strindberg et al. 2018). Up to the early 2000s habitat loss had not been a major threat in the region but will soon pose an serious challenge to their survival, and there is now a very recent and large scale push for conversion of forest habitat to oil palm in the Congo Basin, which will remove suitable habitat if not very carefully managed by appropriate land-use planning (Wich et al. 2012, IUCN 2014).

The meat of all wild animals (“bushmeat”) is eaten throughout Central Africa, both in rural and urban societies. The impact of this threat is on the rise with expanding human populations, improved access along logging roads mentioned above, and by easy access to modern weaponry. The principal reason for killing gorillas is to obtain bushmeat. Gorillas are sometimes deliberately hunted, and also fall victim to snares set in the forest for other mammals such as antelopes; in almost all cases the meat is then either eaten locally in villages or in logging (or mining) camps and/or sold to bushmeat traffickers and transported by logging vehicles or public transport to regional towns and major cities. (IUCN 2014). It should be stressed that gorilla meat is not a food security issue; it is extremely rare for any individual villager to eat gorilla meat, as they are so rare, and in addition, large animals are most favoured by the urban markets. Villagers eat the small antelopes and duikers that they catch, and sell the large species. Live infants for the pet trade are an additional byproduct, as they can sometimes be sold for a higher sum than the value of their meat. A very small proportion of gorillas are killed for body parts for traditional medicine. Although killing or capturing gorillas is illegal in every range state, laws are often poorly enforced.

The risk of disease transmission between humans and gorillas is also increasing as formerly remote forests are opened up for resource extraction and settlement. Ebola caused several massive western gorilla die-offs in some of the most remote parts of the species’ range, which are hugely important sites for their conservation (Williamson & Butynski 2013). While the transmission dynamics of Ebola are not well understood, some predict that Ebola epidemics will reach most of the western gorilla’s current range within the next decade (Williamson & Butynski, 2013).

Even low levels of hunting are unsustainable for western lowland gorillas, as their reproductive rate is very slow- even slower than mountain gorillas (Breuer et al. 2009). The addition of Ebolavirus to hunting is catastrophic: Ryan and Walsh (2011) calculated that recovery of a population post-Ebola would take 75–131 years in the (unlikely) absence of poaching.

Conservation

Many national, regional and international organisations are working to protect the western lowland gorilla through conservation and research programmes. Almost all (80%) of these gorillas live outside protected areas, either in logging concessions or in the swamp forests of Northern Congo; 21% are in Forest Stewardship Council (FSC) - certified logging concessions, which are protected by guards. Indeed, the largest single population lives in an FSC-certified concession in northern Congo. However, 59% of the population lives in areas unprotected by guards (covering 77% of their range) (Strindberg et al 2018).

Several western gorilla sites straddle international borders which require cooperation between two or more countries for effective conservation. One such cross border initiative is the Sangha Tri-National Landscape that includes southern CAR, northern Congo, and southeast Cameroon. This conservation initiative covers the contiguous Dzanga-Ndoki, Nouabalé-Ndoki and Lobéké national parks, and divides the area into regions in which human activity is managed or restricted, and allows for joint patrols by armed rangers from the three countries. It was listed as a World heritage Site in 2012 (UNESCO 2012).

In general, research is usually correlated with better protected sites (Laurance 2013). Research programmes are natural partners to local conservation initiatives. Long-term studies of western lowland gorillas began at Lopé in Gabon in 1983, and expanded to Mbeli in Republic of Congo, Bai Hokou in CAR and Loango in Gabon. All have proved helpful in discouraging poaching. There are a few established tourism operations based around sightings of western gorillas in CAR, Congo and Gabon, including low impact observations from platforms at the edges of the swampy clearings (bais) favoured by the great apes and other animals.

In addition to these field efforts, sanctuaries housing orphaned gorillas have been established in Cameroon, Gabon and Congo. These confiscated great apes are cared for and used to deliver conservation messages to local populations about the plight of this endangered species and their forest homes. Some success re-introducing a small number of rehabilitated gorillas in Gabon and Republic of Congo has also been achieved.

The large geographic range of the western lowland gorilla, political will for conservation, and sparse human population in much of this range, means it has fared relatively well, even in non-protected areas (Tutin et al. 2005). Despite this, the long term survival of western lowland gorillas will require a synergistic approach that includes more effective conservation strategies and enforcement of government policies (Tutin et al. 2005). In 2005, over 70 experts were convened to develop a regional strategy and action plan for the conservation of western lowland gorillas and central chimpanzees Pan troglodytes troglodytes, which are sympatric over most of their range. The result was a regional action plan that identified seven exceptional and five important areas along with priority activities necessary for the great ape’s survival (Tutin et al. 2005).

Based on the best available data and knowledge, the experts identified priority areas in western lowland gorilla conservation, based on the size and extent of great ape populations: Odzala-Lossi-Pikounda-Ngombe-Ntokou complex, Republic of Congo; Lac Télé-Likouala complex, Republic of Congo; Sangha Trinational complex, Republic of Congo, Cameroon and CAR; Loango-Moukalaba-Doudou/Gamba complex, Gabon; Dja conservation complex, Cameroon; Boumba-Bek-Nki complex, Cameroon; and Lopé/Waka complex, Gabon. Protection of these great ape populations would guarantee the survival of the majority of great apes remaining in the region, and represent a highly effective investment given the protection that would be afforded to other native fauna and flora (Tutin et al. 2005).

Priority actions for specific sites were identified along with overarching knowledge gaps. Priority actions attached to particular sites include: a disease surveillance programme and rapid response structure; bio-monitoring and baseline surveys where appropriate (Ebo-Ndokbou conservation complex, Cameroon; and Maiombe Forest Transboundary Initiative, Republic of Congo and Democratic Republic of Congo were identified as priorities for surveys); capacity building for research skills generally and standardised protocols for bio-monitoring training and implementation; improvement of judicial and law enforcement structures; development and promotion of national and transboundary structures; development and promotion of responsible great ape tourism; establishment and maintenance of basic management infrastructure at a site level; reactivation and maintenance of permanent great ape research areas; establishment of community-based biodiversity enterprises; and public education and awareness programmes (Tutin et al. 2005).

In addition to prioritizing areas and activities, the action plan also identified overarching gaps in knowledge needed to effectively conserve western lowland gorillas. Some of these knowledge gaps have been successfully bridged. Best practice guidelines have been developed for survey and monitoring of great ape populations to improve estimates of great ape abundance (Kuhl et al. 2008). The A.P.E.S Portal has improved accessibility to data by providing a centralized database with geo-referenced great ape survey data. Ongoing activities are focused on: large-scale survey and monitoring (establishment of a regional monitoring programme to coordinate surveys and ensure consistency of monitoring methods); capacity building opportunities in great ape research, monitoring methods and technical support for national researchers; and more research on Ebola (transmission dynamics and potential control measures, and evaluation of alternative vaccine delivery methods for great ape populations (IUCN 2014, Strindberg et al. 2018).

Experts believe that implementation of the plan, if successful, would guarantee the survival of the majority of great apes remaining in the region. Many other species would benefit along with the endangered Western lowland gorilla. In addition to site-specific and general knowledge gaps, the plan provides a series of immediate response needs and longer-term mitigation strategies for the three main threats consistent across the region (poaching, disease and logging). Crucially anti-poaching, it is argued, should be the foundation upon which all other great ape conservation activities rest, as it is the most effective means of protecting great apes in western equatorial Africa (IUCN 2014).

References

Breuer, T., Breuer-Ndoundou Hockemba, M., Olejniczak, C., Parnell, R.J. & Stokes, E.J. (2009). Physical maturation, life-history classes and age estimates of free-ranging western gorillas - insights from Mbeli Bai, Republic of Congo. American Journal of Primatology 71: 106–119.

IUCN (2014). Regional action plan for the conservation of western lowland gorillas and central chimpanzees 2015–2025. IUCN SSC Primate Specialist Group, Gland, Switzerland.

Kühl, H., Maisels, F., Ancrenaz, M. & Williamson, E.A. (2008). Best Practice Guidelines for Surveys and Monitoring of Great Ape Populations. IUCN SSC Primate Specialist Group, Gland, Switzerland.

Leendertz, S.A.J., Wich, S.A., Ancrenaz, M., Bergl, R.A., Gonder, M.K., Humle, T., Leendertz, F.H. (2017). Ebola in great apes: current knowledge, possibilities for vaccination, and implications for conservation and human health. Mammal Review 47: 98–111.

Maisels, F., Strindberg, S., Breuer, T., Greer, D., Jeffery, K. & Stokes, E.J. (2018). Gorilla gorilla ssp. gorilla. The IUCN Red List of Threatened Species 2018: e.T9406A136251508.

Laurance, W.F. (2013). Does research help to safeguard protected areas? Trends in Ecology & Evolution 28: 261–266.

Ryan, S.J. & Walsh, P.D. (2011). Consequences of non-intervention for infectious disease in African great apes. PLoS One 6: e29030.

Strindberg, S., Maisels, F., Williamson, E.A., Blake, S., Stokes, E.J., Aba’a, R., Abitsi, G., Agbor, A., Ambahe, R.D., Bakabana, P.C., Bechem, M., Berlemont, A., Bokoto de Semboli, B., Boundja, P.R., Bout, N., Breuer, T., Campbell, G., De Wachter, P., Ella Akou, M., Esono Mba, F., Feistner, A.T.C., Fosso, B., Fotso, R., Greer, D., Inkamba-Nkulu, C., Iyenguet, C.F., Jeffery, K.J., Kokangoye, M., Kühl, H.S., Latour, S., Madzoke, B., Makoumbou, C., Malanda, G.-A.F., Malonga, R., Mbolo, V., Morgan, D.B., Motsaba, P., Moukala, G., Mowawa, B.S., Murai, M., Ndzai, C., Nishihara, T., Nzooh, Z., Pintea, L., Pokempner, A., Rainey, H.J., Rayden, T., Ruffler, H., Sanz, C.M., Todd, A., Vanleeuwe, H., Vosper, A., Warren, Y. & Wilkie, D.S. (2018). Guns, germs, and trees determine density and distribution of gorillas and chimpanzees in Western Equatorial Africa. Science Advances 4: eaar2964.

UNESCO (2012). State of conservation of World Heritage properties inscribed on the World Heritage List: Item 7bAdd. Thirty-sixth session of the World Heritage Committee, p. 218. UNESCO, St Petersburg, Russia.

Walsh, P., Abernethy, K., Bermejo, M., Beyers, R., de Wachter, P., Ella Akou, M., Huijbregts, B., Idiata Mambounga, D., Kamdem Toham, A., Kilbourn, A.M., Lahm, S., Latour, S., Maisels, F., Mbina, C., Mihindou, Y., Ndong Obiang, S., Ntsame Effa, E., Starkey, M.P., Telfer, P., Thibault, M., Tutin, C.E.G., White, L.J.T. & Wilkie, D. (2003). Catastrophic ape decline in western Equatorial Africa. Nature 422: 1–3.

Wich, S.A., Garcia-Ulloa, J., Kühl, H.S., Humle, T., Lee, J.S. & Koh, L.P. (2014). Will oil palm’s homecoming spell doom for Africa’s great apes? Current Biology 24: 1659–1663.

Williamson, E.A. & Butynski, T.M. (2013). Gorilla gorilla western gorilla. In: Mammals of Africa. Volume II: Primates. T.M. Butynski, J. Kingdon & J. Kalina (eds.). Bloomsbury Publishing, London, UK, pp. 39–45.