When CIRAD statistical expertise is at the service of the conservation of gorillas

A report(1) published by the Wildlife Conservation Society (WCS), Fauna & Flora International (FFI) and the Institut Congolais pour la Conservation de la Nature (ICCN) has revealed that between 1995 and 2015, Grauer's gorilla (Gorilla beringei graueri ) numbers fell from 17 000 to around 3800. According to its authors, this 77% reduction in numbers warrants the Grauer's gorilla's classification as "critically endangered" (CR) as per International Union for the Conservation of Nature (IUCN) criteria.

"CIRAD contributed to the study by providing the tools and statistical expertise that enabled estimates of the size of the residual gorilla population based on a partial sample", Ghislain Vieilledent, a CIRAD researcher and co-author of the report, explains. The hSDM software(2), developed by CIRAD, enabled accurate estimates of the Grauer's gorilla distribution area.

This gorilla, which can measure up to 1.83 m and weigh up to 225 kg, is currently the world's largest primate. It lives in the forests of eastern Democratic Republic of Congo (DRC), between the Lualaba River and the Burundi-Rwanda-Uganda border. Unfortunately for the great apes, since 1996, eastern DRC has been plagued by insecurity and anarchy. The mass influx of refugees fleeing Rwanda following the 1994 genocide destabilized the region, triggering two successive civil wars. Although the second has officially been over since 2003, numerous militia groups have settled in the region and established mining camps to fund their operations. As a result, tin (cassiterite), tungsten, diamonds and coltan (a metal used in mobile phones and computer hardware) are being extracted with no heed for any regulations, by miners who make part of their living from bushmeat. Because of their size, the great apes (gorillas and chimpanzees, which are also significantly affected, albeit less so) are among the preferred species, and are often poached.

The steps to be taken to remedy the situation and stop the collapse of Grauer's gorilla numbers - disarming militia groups, regulating mining operations, raising awareness among local people, developing alternative sources of income to mining, monitoring and protecting gorilla populations, setting up community reserves and relocating villages within those reserves - call for substantial human and financial resources and unfailing political commitment. The challenge is huge, but it is the price to pay to avoid losing one of the four known sub-species of gorilla. In effect, if the decline in numbers continues at the current rate (around 5% per year), the sub-species could die out within the next few years.

Literature

(1) Plumptre, A.J., Nixon, S., Critchlow, R., Vieilledent, G., Nishuli, R., Kirkby, A., Williamson, E.A., Hall, J.S., & Kujirakwinja, D. (2016). Status of Grauer’s Gorilla and Eastern Chimpanzee: Historical and current distribution and abundance. Unpublished Report to ARCUS Foundation, USAID and US Fish and Wildlife Service. ISBN 10: 0-9792418-5-5. Available here: www.albertinerift.org

(2) Vieilledent, G., Merow, C., Guélat, J., Latimer, A.J., Kéry, M., Gelfand, A.E., Wilson, A.M., Mortier, F. & Silander, J.A. (2014). hSDM: hierarchical Bayesian species distribution models. Available here: R package version 1.4, doi: 10.5281/zenodo.48470