Explanation for elephant dieoff

Back in July, we brought you the tragic news of a mass elephant die-off in Botswana’s Okavango Delta: hundreds of the animals were found dead. Originally, the cause was unknown, but, this week, Botswana’s Department of Wildlife and National Parks think they’ve identified the culprit: blue green algae in stagnant water. Phil Sansom spoke to conservationist Vicky Boult, from the University of Reading…

Phil - The first of the elephant deaths were reported back in March. Then from May, the carcasses started appearing in droves.

Newsreader - 169 elephant carcasses were found. By June, that number had risen to over 350.

Phil - Some look like they died incredibly quickly, keeling over onto their knees and faces. Others were reported looking disoriented, walking around in circles before eventually collapsing.

Newsreader - This is deeply troubling. Elephants don't just drop dead for no apparent reason.

Phil - For Africa's largest elephant herd, this unknown devastation looked like an existential disaster. Among all the possible reasons that were suggested, from starvation to dehydration, to deliberate poisoning, Niall McCann from the UK charity National Park Rescue mentioned the following on The Naked Scientists -

Niall - The least likely is that this is a natural toxin. Something like anthrax or a blue-green algae. If it was any of those things, we'd be expecting to see many other species also coming as well.

Phil - Well Botswana's government have just announced that this is indeed the reason.

Vicky - Tests have revealed that it is a cyanobacteria, which is a blue green algae that lives in water bodies.

Phil - [That was] elephant conservationist, Vicky Boult.

Vicky - Cyanobacteria are in many water systems across the world, but they become toxic when they bloom. We call it an algal bloom, which is just a mass generation of new cells, new bacteria. And we see these like blue, green scummy layers on top of water bodies, which is why it's called blue green algae. Usually that water body should be quite warm and nutrient rich and also slow moving or stagnant.

Phil - There's certain types of this blue green algae, this cyanobacteria, that produce neurotoxins. Toxins that hurt your nervous system. Make it start to shut down.

Vicky - You might see symptoms such as confusion, muscle weakness, muscle spasms. And that actually aligns quite closely with some of the symptoms that were reported in these elephants.

Phil - Interestingly, these blue green algae may have actually been the cause of some prehistoric mass elephant die-offs, which would be a bizarre turn of events because there's no record of them happening since. Until possibly now. And why here, in this part of Botswana in the Okavango Delta?

Vicky - The area where these elephants have died is very much enclosed from the broader ecosystem. There are fences separating Namibia from Botswana, but also a veterinary fence, which keeps wildlife and livestock from intermixing. The only other water source that's not a small stagnant pond is the Okavango pan handle. But for elephants to access that they have to move through human settlements and through farmland. So that cleaner water potentially is not readily accessible to them, which may have forced them to use these toxic water bodies.

Phil - No other wildlife species on the planes were affected by this toxic water. And even scavengers like hyenas and vultures that we're seeing feeding on the elephant carcasses showed no signs of illness.

Vicky - There's a couple of possibilities why we're not seeing that. Firstly, it might be that just due to an elephant's sheer size, they drink a huge amount of water and perhaps it's the amount of water and therefore the amount of toxins that they're ingesting. The other option is that elephants and elephant carcasses are very well monitored in Africa. And so it's possible that actually we're recording these dead elephants and not recording anything else because other things are harder to survey or less important to survey.

Phil - Both of these are just theories at the moment.

Vicky - I have seen a lot of people online, still quite skeptical. And I think that's mostly based upon the lack of transparency in the reporting from the Botswanan government. We have very little idea of exactly what samples were taken from the elephant carcasses, but also from the water sources and the broader environment. But we also haven't seen the pure lab results.

Phil - Like we reported last time on the programme when we covered this story, this is bad news for elephants as a whole, because back when researchers just didn't know what this was, there was a worry that this could sweep through the whole of the elephant population, and become their equivalent disaster while coronavirus sweeps through us. If it is the blue green algae, though, then we might hope that this is a limited area, not going to happen now that the temperatures are going down. But if this indeed is something that happened this summer because of warmer temperatures, then who's to say it won't happen next summer or the summer after that?

Vicky - It might be that we've seen the perfect climatic conditions for causing these blooms. Potentially a worry as we're moving into a warming world under climate change, we might start to see some of these algal blooms happening more often.