What you may not have read about the scary decline in Grauer's Gorilla numbers

Cover of the WCS and FFI Report

Over a week ago, a report from Wildlife Conservation Society and Fauna and Flora International hit the press about Grauer's gorillas (Gorilla beringei graueri).  Grauer's gorillas, previously known as eastern lowland gorillas, are one of four subspecies of gorillas. Consuming fruits and vegetation, Grauer's gorillas are the largest subspecies. They are listed as endangered and are found only in the Democratic Republic of Congo (DRC).

They made the headlines, and not just on the science news sources, because the latest data shows their numbers have declined dramatically. Over the past twenty years, Grauer's gorilla numbers have declined by an astonishing 77%, with only 2, 585 animals estimated alive today. Their range has been reduced by 84-93%. If you saw this on the news, you probably also saw that civil unrest and other human pressures are the reasons behind the sudden decline. This is hardly surprising.

What you may have missed are some of the more nuanced details behind these numbers, details that can be found in the report itself, which also covers chimpanzees in the same area. In their report titled, "Status of Grauer's Gorilla and Chimpanzees in Eastern Democratic Republic of Congo: Historical and Current Distribution and Abundance," we learn that increases in agriculture and the availability and use of shot guns caused habitat loss and extinctions of local populations in the 60s and 70s. Surveys done in the 90s also suggested species decline due to expanding human populations and hunting. The late 90s and early 2000s saw these threats exacerbated when refugees from civil war in Rwanda, internally displaced people, and armed groups in the DRC put further pressure on DRC forests and wildlife. This influx of people needed fuel for firewood, land for agriculture, timber, and also hunted wildlife and mined.

The main threats to Grauer's gorillas are hunting for bushmeat and habitat loss due to the spread of agriculture. Hunting practices are related to artisanal mining though. These mines are found adjacent to or even in protected areas, are illegal, and are controlled by armed militias (Kirkby et al., 2015). They allow people an economic opportunity to earn an income quickly and attract people from multiple social classes(Kirkby et al., 2015). Once working at these remote mines, miners rely on bushmeat for food and consume primates and other large mammals(Kirkby et al., 2015). The miners aren't evil people though, as many said they wouldn't hunt bushmeat if alternatives were available and also said they wanted to leave the mining industry.

SMART patrols, reconnaissance surveys, transects, and occupancy surveys were used to determine gorilla decline and show that one of the areas with the highest number of animals, Kahuzi-Biega National Park saw a decline of 87% in gorilla density, and this is with a portion of the Park protected reasonably well. Seven of the eleven sites surveyed through encounter rates show an average decline of 94%. These findings are enough to support raising the IUCN status of Grauer's gorillas to critically endangered.

Occupancy probability model from report. Blue areas
mean high likelihood and red very low likelihood of gorillas

Behind these alarming numbers, a story emerges of people pushed beyond their limits and forced to use the forests available in order to survive. Civil war, changes in government, and general civil unrest gives the DRC its tumultuous historic timeline, the effects of which not only impact people but also the flora and fauna of the region. Some may find it easy to forget, but humans and nature are intricately linked.

You may think you have no connection to this story other than one as an innocent bystander, but the resources mined from the DRC are part of an industry many of us play into. Most of the mines are for cassiterite, gold, coltan, and wolframite. The first is an important source of tin, the second you may be wearing now, coltan is used in electronics such as our cell phones, and the last is an important source of tungsten. Given that mining is one of the main reasons Grauer's gorillas are threatened, chances are many of us are connected to this problem, as uncomfortable as that may make us feel.

Links of potential interest
IUCN Page for Grauer's Gorillas
IUCN Categories and Their Criteria
BBC's Country Profile of the DRC

Works cited:

Kirkby, A., Spira, C., Bahati, B., Twendilonge, A., Kujirakwinja, D., Plumptre, A., ... & Nishuli, R. (2015). Investigating artisanal mining and bushmeat around protected areas. Unpublished report to USAID and Arcus Foundation.

Plumptre, A.J., Nixon, S., Critchlow, R., Vieilledent, G., Nishuli, R., Kirkby, A., Williamson, E.A., Hall, J.S. & Kujirakwinja, D. (2015). Status of Grauer’s gorilla and chimpanzees in eastern Democratic Republic of Congo: Historical and current distribution and abundance. Unpublished report to Arcus Foundation, USAID and US Fish and Wildlife Service.