Keep your distance: using Instagram posts to evaluate the risk of anthroponotic disease transmission in gorilla ecotourism.
Mountain gorilla Gorilla beringei beringei trekking is a substantial source of revenue for the conservation of this threatened primate and its habitat. Trekking, however, may pose a threat of human-to-gorilla disease transmission that could have disastrous effects on wild gorillas. We used 858 photographs posted on Instagram in 2013-2019 to analyse the proximity of tourists visiting mountain gorillas in the wild. We classified photographs of the encounters according to the distance between the closest gorilla and human, the age class of the gorilla, the trekking location and presence of a surgical face mask on the tourist. We ran a generalised linear mixed model to test whether these variables influenced the distance between the human and the wild gorillas in the photographs, and to test whether these distances have changed over time. Most sampled photographs (86%) showed tourists within a critical 4 m of the gorillas, with 25 incidents of physical contact between a tourist and a gorilla, and only 3% at the recommended distance of 7 m or more. We only were able to record face mask use in the Democratic Republic of Congo, where these were present in 65% of uploaded photos. Tourists and immature gorillas tended to get closer to each other than tourists and adult gorillas, and this is more pronounced in female tourists than male tourists. The mean distance between human and wild gorillas decreased by ~1 m between 2013 and 2019. The results indicate that existing rules are not enforced and raise attention to this unsustainable aspect of mountain gorilla trekking as it is practiced today. These ever-growing tourist attractions in the range countries pose risks of disease transmission in both directions between tourists and wildlife. The popularity of photograph-based social media may stimulate closer contacts and influence people into risky behaviours. We advocate the establishment and reinforcement of regulations relating to the distance between animals and tourists in any in situ wildlife ecotourism context, as well as campaigns to raise awareness regarding the risks of anthroponosis, and fines applied in case of non-compliance.