Aerial images of some of the elephant carcasses seen in the Okavango Delta
Toxins in water produced by cyanobacteria killed more than 300 elephants in Botswana this year, officials said on Monday, announcing the result of an investigation into the deaths which had baffled and alarmed conservationists.
Cyanobacteria are microscopic organisms common in water and sometimes found in soil. Not all produce toxins but scientists say toxic ones are occurring more frequently as climate change drives up global temperatures.
Cyril Taolo, deputy director of the Department of Wildlife and National Parks, told a news conference the number of elephant carcasses found since deaths were first reported around early May had risen to 330, from 281 in July.
"What we just know at this point is that it's a toxin caused by cyanobacteria," said Taolo, adding the specific type of neurotoxin had yet to be established
Authorities will monitor the situation during the next rainy season, and Taolo said for now there was no evidence to suggest that Botswana's wildlife was still under threat as officials were no longer seeing deaths
The department's principal veterinary officer Mmadi Reuben told the same news conference that questions remained as to why only elephants had been affected.
Other animals in the Okavango Panhandle region appeared unharmed.
Some cyanobacterial blooms can harm people and animals, and scientists are concerned about their potential impact as climate change leads to warmer water temperatures, which many cyanobacteria prefer.
Southern Africa's temperatures are rising at twice the global average, according to the Intergovernmental Panel on Climate Change.
"It amounts to having the right conditions, in the right time, in the right place and these species will proliferate," Patricia Glibert, a professor at the University of Maryland Center for Environmental Science, who has studied cyanobacteria, told Reuters.
"These conditions are coming together more often, in more places, so we are seeing more of these toxic blooms around the world."In neighbouring Zimbabwe, about 25 elephant carcasses were found near the country's biggest game park
and authorities suspect they succumbed to a bacterial infection.
The animals were found with tusks intact, ruling out poaching and deliberate poisoning. Parks authorities believe the elephants could have ingested the bacteria while searching for food. The carcasses were found near water sources."We considered the possibility of cyanobacteria but we have no evidence that this is the case here (in Zimbabwe),"
said Chris Foggin, a veterinarian at the Victoria Falls Wildlife Trust, which tested samples from dead elephants from Zimbabwe and Botswana.
Zimbabwe has sent samples to Britain and is waiting for permits to send samples to two other countries, Foggin said.
Africa's overall elephant population is declining due to poaching but Botswana, home to almost a third of the continent's elephants, has seen numbers grow to around 130,000.
Not only do the researchers have no hard evidence, but they don't sound very sure of their conclusions. This makes sense because elephants are likely to have encountered cyanobacteria before - the water would likely stink and the bacteria would form a bloom
, alerting the elephants to it's presence - and so it's unlikely all of them would make the same mistake of drinking copious amounts of contaminated water; moreover, this doesn't explain those that died, also en masse, in neighbouring Zimbabwe. So the question still remains, what led to the mass death of these elephants?
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that the investigation hasn't convinced everyone and that more research is needed to identify the cause of death:
The elephant deaths dropped off near the end of June, as the pans and watering holes dried up and the species of cyanobacteria that produces neurotoxins died.
Tests were conducted in laboratories in South Africa, Canada, Zimbabwe, and the United States, though local officials in Botswana declined to name specific labs or agencies. The same officials vowed to conduct more testing of waterholes for algal blooms ahead of future rainy seasons to prevent similar die-offs from reoccurring.
These kinds of toxins were initially ruled out as the cause of the die-off, as only one other animal, a horse, died in close proximity to watering holes and in similar circumstances to the elephants. Scientists now suspect that prolonged exposure to the cyanobacteria due to bathing and additional drinking time among elephants may explain the discrepancy.
However, conservationists such as Dr Niall McCann, director of conservation at UK-based charity National Park Rescue, have called for increased research into the algal blooms believed to be responsible so the wildlife community can better protect the pachyderms.
McCann also decried a lack of more thorough testing of the elephant carcasses, which must be done in a highly specific and timely manner, to better narrow down and explain the die-off events.
"Just because cyanobacteria were found in the water that does not prove that the elephants died from exposure to those toxins. Without good samples from dead elephants, all hypotheses are just that: hypotheses," said McCann, highlighting that correlation doesn't equal causation, especially if there is to be any real hope of protecting the animals in future.
One leading theory is that they were felled by a strain of a bacteria called pasteurella, which killed hundreds of thousands of Saiga antelope in Kazakhstan in 2015.