Why crocodiles in South Africa are losing their teeth

The likely culprits are lead-based fishing weights

Ethan Freedman
Climate Reporter, New York
Thursday 09 June 2022 11:05
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1 In 5 Reptiles Threatened With Extinction

Crocodiles in a South African lake are being found with missing and fragmented teeth — and lead poisoning is probably to blame.

Researchers studying Nile crocodiles in Lake Saint Lucia, along the country’s east coast, found reptiles with massively high lead levels in their blood, which they attribute to lead weights used in fishing.

This threat to the local crocodiles requires “urgent attention”, says the study, published last week in Chemosphere.

The team took samples from 22 wild crocodiles, as well as three captive crocs from a local conservation centre. While the three captive crocodiles had an average of 208 nanograms of lead per millilitre of blood, some of the wild males had more than 1,000 ng of lead per millilitre.

Of those, five had more than 6,000 ng per millilitre — and one had a whopping 13,100 ng per millilitre. Researchers noted signs of lead poisoning in all five of those crocodiles, with four showing “loss of many teeth” and one seeming anaemic. The worst tooth loss showed up in the crocodile with 13,100 ng of lead per millilitre.

Lead — which accumulates in the bodies of many animals, including humans — can often pile up in crocodile bones and teeth, and could be hampering dental health, the study notes. In addition, anaemia as a result of lead poisoning has been documented in other species, they add.

The source of the lead is likely lead-based fishing weights, the authors say. Other lead products, like bullets, have been found to harm wildlife as well — and efforts to reduce lead exposure in wildlife has helped populations, they note.

For example, after lead fishing weights were regulated in Britain in 1987, the mute swan populations doubled in the decades following.

“At Lake St Lucia, the case for discontinuing the use of [lead] in fishing activities is clear,” the paper says.

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