Drought in the Amazon can cause local caiman extirpations, spike human-caiman conflict

Drought conditions have previously been cited as a potential factor in increased alligator attacks on humans

By Brandon Sideleau
Published: Monday 30 October 2023
The black caiman is a crocodilian endemic to South America. It is an apex predator of the Amazon, along with the jaguar and the green anaconda. Photo: iStock

The Amazon river basin is currently experiencing a severe drought, which has caused the region’s waterways to reach their lowest levels since the early 20th Century. A combination of anthropogenic climate change and El Nino are the likely culprits behind the abnormally dry conditions.

The drought has had a devastating effect on the region’s air quality, due to nearly 3,000 wildfires in the surrounding rainforest, which has effectively become kindling in the parched circumstances. In addition, the receding river has left many boats stranded on dry banks, thus cutting off the region’s main mode of transportation.

The drought has also had a catastrophic impact on much of the basin’s diverse wildlife. Abnormally hot water temperatures, combined with disease, pollution, and low water levels, resulted in the deaths of at least 100 Amazon River dolphins (Inia geoffrensis), a species listed as Endangered by the International Union for Conservation of Nature Red List of Threatened Species. In many areas, water temperatures exceeded 102 F or 38.8 degrees Celsius.

The Amazon river basin is also home to four different species of caiman — the black caiman (Melanosuchus niger), spectacled caiman (Caiman crocodilus), Cuvier’s dwarf caiman (Paleosuchus palpebrosus), and smooth-fronted caiman (Paleosuchus trigonatus).

Like the Amazon River dolphin, the region’s caiman species are also likely to be adversely affected by the extreme conditions. Such droughts have caused mass caiman death in the recent past.

During northern Paraguay’s severe 2016 drought populations of yacare caiman (C. yacare) were eradicated from many areas along the Pilcomayo River. The parched conditions result in large congregations of caiman into ever shrinking pools of water.

Eventually, many of these pools dry up entirely and the caiman must travel over land in search of new pools. Any caiman unable to accomplish this are likely to die in the drying mud.

Though the large caiman populations in Brazil (numbering in the tens of millions) mean that even extreme drought is unlikely to significantly impact the overall status of each species range-wide, it can cause significant reductions (and even extirpations) in many areas.

Another potential and, perhaps, unexpected outcome of the drought could be increased human-caiman conflict. The American alligator (Alligator mississippiensis) is a crocodilian species closely related to caiman (all members of the Alligatoridae family).

Drought conditions have previously been cited as a potential factor in increased alligator attacks on humans. In May of 2006, three fatal attacks were reported within a span of one week in Florida.

A severe drought at the time had caused higher densities of alligators to crowded into limited habitat, resulting in more alligators wandering to find food and less crowded waterways.

A similar scenario could also occur in parts of the Amazon basin, particularly involving the black caiman, which can reach and possibly even exceed the American alligator in size. While it is unclear how many caiman attacks go unreported along the vast river basin, particularly in remote areas, at least one serious black caiman incident has already occurred during the drought. On October 15th, a 49-year-old fisherman was attacked along the main channel of the Amazon at the Mambeca community of Santarem, in Para state.

Brandon Michael Sidealeau is a PhD student studying human-saltwater crocodile conflict, Charles Darwin University

Views expressed are the author’s own and don’t necessarily reflect those of Down To Earth

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