Mass elephant deaths of 2020 in Africa possibly due to climate-induced poisoning, study finds

Climate change may have induced a poisoning in water that elephants drank, thereby causing mass deaths in 2020 in Botswana, Africa, according to a new study that provided satellite evidence.

In May and June 2020, more than 350 elephants died in northern Botswana under "mysterious" circumstances, according to a report by The Guardian.

While poaching was soon ruled as a cause for these deaths, toxins produced by algae growing in waterholes was suspected to be one, even as evidence has remained inconclusive, researchers, led by those at King's College London, UK, said.

This was because the mass deaths occurred during the COVID-19 pandemic when movements were restricted, thereby preventing the collection of samples at the time, they said.

However, 25 elephants deaths from neighbouring Zimbabwe due to septicaemia or blood poisoning in the same year cast some doubt on algae toxins being the reason for the Botswana deaths, the researchers said.

Now, the team has published evidence in the journal Science of The Total Environment, that shows toxic algae was the cause. Satellite data was used to analyse the link between 3000 waterholes and locations where the elephants died.

The analysis revealed that waterholes near the animal remains showed higher levels of algae and repeated "bloom" or algal growth events in 2020 compared to previous years –particularly during the period when the mass deaths occurred.

The animals were very likely poisoned by waterholes where toxic blooms of blue-green algae or cyanobacteria, had developed after a very wet year followed a very dry one, according to the lead author Davide Lomeo, a PhD student in the Department of Geography at King's College London.

"Botswana is home to a third of all African elephants, and this unprecedented die-off within their largest remaining population underlines the escalating concerns surrounding the impact of drought and climate change on the Okavango Delta (where carcasses were first spotted), one of the most important ecosystems in the world," Lomeo said.

The researchers also found that decayed elephant carcasses were more spread out across the landscape, compared to fresh ones, indicating that the die-off in 2020 was different from typical patterns of death.

"We identified 20 waterholes near fresh carcasses that experienced increased algal bloom events in 2020, compared to the previous three years combined. These waterholes also exhibited the highest average algal biomass of the period 2015-2023," Davide said.

With southern Africa projected to become drier and hotter due to climate change, waterholes in this region could be drier for more months of the year, Davide said.

"Our findings point to the potential negative effects on water quantity and quality, and the catastrophic repercussions on animals, this could have," the lead author said.