In May and June 2020 over 330 African Bush Elephants, Loxodonta africana, were found dead at locations around the Okavango Delta in northern Botswana. The Animals had apparently not been moved after their deaths, their tusks were intact, and they showed no signs of physical injury, which seemed to rule out poaching as a cause (though not the possibility that Humans were to blame, as Elephants are sometimes poisoned as a way to prevent them causing damage to crops). This caused considerable concern to conservationists, as Botswana is home to about a third of Africa's total Elephant population (around 130 000 Animals), meaning that any unidentified threat to Elephants in Botswana could potentially have a significant effect on the species as a whole.
African Bush Elephants, Loxodonta africana, found dead in northern Botswana in May-June 2020). Reuters.
A number of possible causes for the deaths were proposed, including Human activity, disease (particularly Anthrax, which is known to cause mass-deaths of large animals in Southern Africa), and poisoning by natural causes, such as Algal blooms. Scientists from the Botswanan Department for Wildlife and Natural Parks collected extensive samples from both the Elephants and the local environment, which were sent to specialist laboratories in South Africa, Canada, and the United States for testing.
The results of these tests have now been returned, and overwhelmingly support the hypothesis that the Elephants died as a result of neurotoxins produced by Cyanobacterial blooms, which flourished in the waterholes they were using. This fits well with the timing of the deaths, which ceased in June as many of the smaller waterholes in the area were drying up, according to Mmadi Reuben of the Department for Wildlife and Natural Parks. It is possible that Elephants died while other large animals were spared because of the unique way in which Elephants drink, sucking up water with their trunks before passing it to their mouths, rather than lapping it straight from the surface as most Mammals do. This means that they can obtain water from deeper than other Mammals, potentially making them vulnerable to toxins laden Cyanobacterial cells that sink after dying.
Water bodies in Southern Africa (and other parts of the world) have become more vulnerable to Algal blooms in recent years due to rising global temperatures, which often favour bloom events in which single opportunistic species, many of which produce toxins, take over from more balanced phytoplankton communities.
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