New analysis looking at elephant carcass distribution and algae levels in watering holes indicates that climate-induced poisoning has killed over 300 African elephants.
King’s College London researchers have been studying the deaths of 350 African elephants in Botswana (which occurred during a single year in 2020). The researchers have concluded these are the result of drinking from water holes where toxic algae populations have significantly increased due to climate change.
The scientists indicate their analysis shows animals were very likely poisoned by watering holes where toxic blooms of blue-green algae (cyanobacteria). This occurred after a very wet year followed a very dry one.
The loss in numbers is significant. Botswana is home to a third of all African elephants, and this unprecedented die-off underlines concerns surrounding the impact of drought and climate change.
Elephant carcasses were detected in the north-eastern sector of the country’s Okavango Delta between May and June 2020. Poaching was ruled out as the cause. Instead, toxins produced by the algae growing in watering holes was one suspected cause, though evidence has remained inconclusive.
This was determined by combining satellite data and spatial analysis. This enabled the scientists to examine the relationship between about 3000 waterholes and the locations of deceased elephants.
The analysis revealed waterholes near the carcasses showed elevated algal levels and repeated bloom events in 2020 compared to previous years. This was particularly during the period associated with the mass mortality event.
The researchers also showed that decayed elephant carcasses were more spread out across the landscape than fresh carcasses, indicating that the die-off in 2020 was different from typical elephant mortality patterns.
There were 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.
After drinking, elephants were estimated to have walked an average of 16.5 km from the toxic waterholes and died within about 88 hours of exposure.These findings suggest a heightened risk and likelihood of the presence algal toxins in these waterholes.
It is of concern, going forwards, that Southern Africa is projected to become drier and hotter under climate changes, and as a result waterholes across this region will likely be drier for more months of the year.
The research appears in the journal Science of The Total Environment, titled “Remote sensing and spatial analysis reveal unprecedented cyanobacteria bloom dynamics associated with elephant mass mortality.”
