Deadly Waters: Nile crocodiles in the Olifants River in South Africa are mysteriously dying en masse.
Image: Henk Bouwman
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Photos of a South African Croc Crisis
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Carcasses of adult crocodiles do not usually signal the return of winter in South Africa, but mass death seems to be becoming the harbinger of the season. Rangers at the Kruger National Park have found Nile crocodiles floating in the Olifants River or bloated and decaying along its banks. Investigators are rushing to figure out the cause and worry that the deaths might be signaling the presence of toxins or pathogens that could threaten not only the croc population but also the livelihoods of the people living near the river.
The Olifants River runs several hundred kilometers through three South African provinces and into Mozambique. It supplies water to industrial agriculture operations that send food to Europe and to the local rural communities, which also depend on those waters for fishing and farming.
The first sign of croc trouble in the river came in the winter of 2008, when rangers collected 170 dead individuals, sometimes at a rate of 20 bodies a week. A survey at the end of this May showed nearly 400 crocs living in the park’s gorge, down from at least 1,000 in 2008. So far, as of August 7, rangers and scientists have found 23 carcasses.
After slicing open some of the crocodile corpses last year, researchers determined some kind of pansteatitis—an inflammation of adipose tissue—was killing the animals. Specifically, their tails were swollen with the hardened, enlarged fat deposits, which had stiffened and immobilized the crocodiles and left them unable to hunt. Samples of the fat showed the deposits had oxidized to bright yellow.
[Slide Show: Photos of a croc crisis, including an image of the yellow fat]
The disease may not be limited to crocs. Scientists found the same kinds of fat deposits in fish in the Olifants River. And in the river’s gorge just upstream from Massingir Dam in Mozambique, which also has seen croc declines, birds were absent, raising the possibility that they, too, have succumbed to the same agent.
But the cause behind the strange fattening remains a mystery. In June a team led by Henk Bouwman of North-West University, Potchefstroom Campus, in South Africa reported test results from crocodile tissues at two European chemistry meetings. “Everything is there,” Bouwman says, referring to the detection of DDT, PCBs, dioxins and brominated flame retardants, “but nothing is screaming, ‘it’s me, it’s me, it’s me.’ ”
One possibility could be related to dinoflagellates and cyanobacteria found upstream in the catchment, which might be releasing toxins similar to those that cause red tides in marine environments, says Peter Ashton, a water resources specialist at the Council for Scientific and Industrial Research in South Africa and the University of Pretoria.
“It never is a quick, easy solution” in which it takes one test to find a culprit, explains Danny Govender, a disease ecologist for South African National Parks. She notes that samples taken from live crocs in 2007 showed that the fat of some crocodiles was beginning to harden. Along with Bouwman, she hypothesizes that all these toxins, found below harmful levels individually, could be acting together in a deadly brew.
Govender cites changes to the river’s ecosystem that stem from infrastructure outside the park, including hundreds of coal-mining operations upstream, where crocodiles have disappeared almost completely, and a dam downstream of the gorge. For the first time in the two decades since it was built, the dam’s reservoir was full last year, slowing down the Olifants’s flow through the crocodiles’ gorge. Govender wonders if the slowed water enabled toxins to build up along the crocodiles’ stretch of the river. Indeed, hydrogen sulfide, ammonia and other compounds from river sediments probably caused massive fish deaths in July, scientists have concluded, and crocs eating these contaminated fish could have been affected.
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9 Comments
Add CommentThis is just another 'dot' that is connecting to more 'dots' that's making a puzzle picture of the distruction that man is wreaking across the globe. Someday as a race of beings we may figure out that we need to be 'a part' of nature and work in harmony with all the other life instead of being 'apart' from it and thinking we can take what we want and rule the world with no consequences. My fear is that day may come too late for most.
Reply | Report Abuse | Link to thisChuck Norris is killing those crocs.
Reply | Report Abuse | Link to thisI am sorry but sometimes I want to shake those ASSHOLES off until they see what they have done and make them understand responsibility they had ruining our ecosystem! Only why - I have sitting in my mind do we have to watch and experience consequences of what these (normally it comes to one or couple of people who make the decision... and of course those followers who are too scared to say no and not act upon the evil commands they are given!!) did. We are gonna die all! first by destroying ecosystem around us and then suffering from what was done! I very much hope we all get awaken sooner than when it is too late!
Reply | Report Abuse | Link to thisRead "The Culture of Make Believe" and "Endgame" by Derrick Jensen. It will be like waking up...all the way.
Reply | Report Abuse | Link to thisHow the heck does Chuck Norris come into the equation?
Reply | Report Abuse | Link to thisYes, it's a shame that so many animals die due to the ignorance of men, but before you sit and complain about it, perhaps you should consider the part you play. Do you drive a car? Do you use a wood stove? Do you create garbage that is burnt or dumped in a landfill? Do you use cleaning products and beauty aids? Perfume or aftershave? How much plastic do you own? These are the things that create the toxic waste that is not only killing animals, but is killing people. If you live in the industrialized world, you are guilty. And yes, that includes me.
Reply | Report Abuse | Link to thisNow, how much of your lifestyle are you willing to change to save the planet?
Yellow fat disease used to be a well known condition in domestic cats. There are numerous references to it in veterinary literature. The basic cause was a deficiency of vitamin E resulting from a diet that comprised mainly tuna fish. I suggest that before before jumping to an uninformed conclusion that this condition in the Nile crocodiles has a toxic cause, a deficiency of an essential dietary ingredient should be considered. I expect that unaffected crocodiles would have the same foreign chemicals in their tissues as the affected ones.
Reply | Report Abuse | Link to thisnbajzek - priceless.
Reply | Report Abuse | Link to thisRe: Hunting a Croc Killer, SciAm, Oct. 2009: I have some experience with rivers, lakes and reservoirs and have noted from field experience the differences in each. I suspect the key in the epidemiology of the dying crocs may lie in the changes the man-made reservoir has placed on the aquatic ecology of the region. A dam placed on a large river changes everything; physically, chemically and as a consequence the biology also changes, for both aquatic and terrestrial species that formerly depended upon a free flowing stream. The reservoir interupts the natural flow of the region and changes the "seasonal" temperature and chemistry of waters discharging into the tailwater so that the reservoir is not a "natural" lake and the tailwaters are not a "natural" river. Changes in water quality created by the "new" reservoir environment can be quite dramatic. If the reservoir has any depth the standing water will stratify into a temperature gradient from surface to bottom and mixing from the surface will cease, causing also an oxygen gradient where it will completely disappear in the bottom layers and create change in the oxidation/reduction potential (ORP) of this lower region. The lake then essentially becomes an anaerobic septic environment which can cause all manner of problems with solution of products of anaerobic digestion such as methane and will also allow the solution of heavy metals, such as mercury, lead and others. The article also mentions coal mining occurring upstream. Coal is a famous source of all manner of sulfides and toxic metals. Tailings from coal mining entering the reservoir coupled with organic material on the bottom plus the lack of oxygen is a system ripe to generate all manner of toxic substances. Annual fish kills or a lack of fish and/or gill breathing aquatic insects in the tailwaters are a dead giveaway that the lake is generating toxins. Bubbles noted coming up from the bottom of the lake plus rotten egg odors in the discharge are also signs of bad chemistry occurring in the bottom layers of the reservoir. Water entering the resevoir from sidestreams or into the main channel may route through the reservoir as a density current and could conceivable carry toxins through to the tailwater discharge. Since both crocs and fish seem to have the same diagnostic evidence of pansteatitis an epidemiologist would definitely examine the possibility of the newly formed reservoir being the source of toxic chemistry being discharged from the changing ORP occurring within the reservoir.
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