The Crocs That Turned To Rubber

In May 2008, rangers at South Africa’s Kruger National Park stumbled across a horrifying sight in the isolated Olifants Gorge. The gorge, normally a haven for giant Nile crocodiles, was littered with their corpses. Before long, more than 30 dead crocodiles were located, all of which bore no outward signs of injury. The rangers were perplexed as to how these extraordinarily resilient creatures could come to die en masse.

Park authorities immediately launched an investigation into the mysterious deaths, led by ecologists Danie Pienaar and Dr Danny Govender, but no clues were forthcoming. “It was impossible to comprehend that the crocodiles could be suffering this fate in this area of the park that is so far removed from human impact,” Pienaar explains.

However, after conducting post-mortems on some of the dead crocodiles, the team realised that a disease known as pansteatitis was behind the mass die-off. “When we first cut open these crocodiles we noticed this orange, really hard, really rubbery fat,” Dr Govender recalls. “It was like shoe rubber.” Pansteatitis, which is more common in domestic cats, is caused by a combination of consuming too much rancid fat, and a lack of vitamin E. The condition causes fat to solidify, leaving infected creatures lethargic, heavy and unable to hunt, eat, or defend themselves.

Meanwhile, the death toll in Olifants Gorge continued to rise. “"The numbers were just escalating,” Pienaar remembers. “Every day there would be another couple.” Soon, the rangers spotted a crocodile feeding on the corpse of one of its own kind. The crocs had turned to cannibalism, and the only method of preventing the disease from spreading in this way – and potentially into the land predators such as lions – was to remove all the corpses from the gorge. The taskforce embarked upon a massive clean-up operation, which was no easy feat with each corpse weighing more than 200kg. The intervention had an instant effect, and for several months no deaths were recorded.

Before long, the team had another huge setback when pansteatitis appeared to return to the gorge. Another mass die-off claimed the lives of 179 crocodiles. Two months later, a spate of fish deaths occurred – and this time the fish were discovered to be carrying the same disease. The dead creatures were all African sharp tooth catfish – a favourite food of crocodiles. Catfish feed on the bottom of the river, which again led the experts to suspect that pollution might be the cause.

The only thing that appeared to coincide with the start of the deaths was the opening of the controversial Massingir dam, 20 miles downstream and across the border in Mozambique. When the dam opened, water levels in the gorge rose by about 20metres, and the flow of water was dramatically slowed. The gorge was also flooded with a fine, sticky silt that clogged the water.

No one chemical in the water was abundant enough to kill the crocs. However, researchers found around 1,500 toxins in the water – most of them stemming from unregulated mining and sewage disposal. These toxins, coupled with increased silt levels, could have created a toxic soup. The catfish feed on the heavily polluted silt and in turn they are fed upon by the crocodiles, spreading the fatal disease.

However, with the rate at which the crocodiles are dying, Pienaar and Govender believe there is little that can be done to save them. “As sad and depressing as it might sound,” Pienaar says, “I don’t think the crocodiles in this gorge have got much of a future.”