The staggering and unexplained deaths of over 300 African elephants in early 2020 — one of the largest mass mortality events of wild mammals in recent history — was most likely due to toxins in water that proliferated due to climate extremes, according to a fresh analysis of a decade’s worth of satellite data.
The mass death, a “conservation disaster” that occurred over the course of three months in Botswana’s Okavango Delta, saw some elephant carcasses clustered around waterholes and others collapsed face-first on the ground. While the region is a known poaching hotspot, the tusks of the elephants were found intact, ruling out human interference and prompting scientists to look for other causes.
Yet, efforts to establish a definitive cause of the mass mortality event — which would have involved collecting water and tissue samples to directly test for the presence of cyanotoxins — were hindered by the remote location of the Okavango Delta and further complicated by logistical challenges due to the COVID-19 pandemic. The tragedy occurred during the peak of the pandemic, which restricted movement and delayed critical fieldwork, preventing researchers from gathering direct evidence.
Now, however, a study combining satellite observations and aerial surveys of over 3,000 waterholes in the region found elevated algal levels near the deceased elephants, strengthening previous evidence that cyanobacterial neurotoxins — toxic compounds produced by microscopic blue-green algae called cyanobacteria — are the likely culprit behind the mass deaths.
“Algal blooms are routinely monitored by satellite, but this data isn’t often used to investigate mass mortality events,” study lead author Davide Lomeo of King’s College London said in a statement. “As the scale of elephant deaths from unknown causes was much higher than anything that’s been seen before, it’s important to use all sources of evidence to investigate what happened to these endangered animals.”
Cyanotoxin concentrations in African inland water sources are often found to be thousands of times higher than World Health Organization guidelines regarding safe drinking water for animals and humans. Still, satellite images of the Okavango Delta between 2015 and 2023 revealed cyanobacteria blooms had exploded to unprecedented levels during an unusually rainy season in early 2020, following the driest season in decades during the year prior.
This extreme shift from drought to intense rainfall delivered…
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