The lead weights used in fishing are poisoning the crocodiles on Lake Santa Lucia.
- Lake St Lucia crocodiles are losing their teeth and suffering from anemia due to exposure to lead in the water.
- In some cases, blood lead concentrations are 10 to 25 times higher than the levels considered lead poisoning in birds and mammals.
- The lead ends up in the water through the fishing weights that the crocodiles ingest.
The crocodiles of Lake Santa Lucia, part of the World Heritage Site – iSimangaliso Wetland Park – have lost their teeth and suffer from anemia due to their exposure to toxic levels of lead.
Lake St Lucia is known for its wildlife, including hippos. It is an ecotourism destination that includes recreational fishing allowed in some parts. The estuary also provides nursery habitats for young fish.
In the recent past, the estuary’s mouth was closed due to the collection of sediments which negatively affected the biodiversity of the area. The government has examined the impact of the man-made eruption of the river mouth. Floods in KwaZulu-Natal in April contributed to a natural breach in the river mouth, Fin24 previously reported.
a document, Elevated lead exposure and clinical signs of toxicosis in wild Nile crocodiles (Crocodylus niloticus) from a world heritage site: Lake Santa Lucia estuary system, South Africa, which was recently published. It is based on a study investigating the impact of chronic lead exposure on crocodile health.
The blood and tail fat tissues of 25 Nile crocodiles (out of about 1000) were sampled for the study. The samples were collected over two weeks in May and June 2019. A total of 22 crocodiles were from the St Lucia Estuary and three were from the St Lucia Crocodile Center, a conservation facility. Captive crocodiles were assumed to have low lead exposure and serve as a reference for the study.
The document indicates that crocodiles ingest fishing lead, particularly from recreational fishing in the area, which has been happening since the 1930s. This means that adult crocodiles from Lake Santa Lucia have been exposed to lead for several decades.
One of the authors of the paper, Professor Marc Humphries of the Environmental Geochemistry Lab at the University of the Witwatersrand, explained that, like birds, crocodiles are unable to pass ingested lead objects and, as a result, have to cope with a chronic lead poisoning. In some cases, the concentration of lead in the blood was 10 to 25 times higher than the levels considered lead poisoning in birds and mammals.
The paper indicated that the range of measured lead concentrations is higher than previous reports for Lake St Lucia and represents the highest ever reported concentrations for crocodiles worldwide. According to Humphries these are the highest concentrations ever recorded for all vertebrate species (animals with a backbone or spinal column).
The study showed that lead was detected in all 22 wild crocodiles sampled.
The incidence of lead poisoning was higher in male than female crocodiles. This difference is behavioral: adult male Nile crocodiles are 20% larger than females and may have a greater tendency to ingest larger items, the paper reads.
“Dominant males may also be more opportunistic in their feeding strategy, targeting fishing lures more frequently, thereby increasing the likelihood of Pb. [lead] weight ingestion in males “.
Lead accumulates in the bones and dental tissues and replaces calcium. Deteriorates teeth and causes loss.
Supplied Marc Humphries
Although most of the crocodiles appeared to be in good physical condition, they suffered from anemia and tooth loss. These are symptoms seen in birds and mammals with lead poisoning.
“… We noticed that many of the sampled males had broken and missing teeth. One crocodile appeared abnormally pale in color and showed obvious signs of lethargy both during capture and release. We suspected this individual was suffering from severe anemia.” it reads in the document.
Tooth loss contributes to “nutritional stress” and death. Although the consequences of anemia are unknown, extreme cases can lead to sick and weak crocodiles which may be susceptible to disease and may be at risk for predators (mainly other crocodiles).
In addition to the blood and tooth disorders found in crocodiles – which will affect their long-term survival – it could also affect their reproductive systems, but that warrants further research, the paper indicated.
So far, research shows that high concentrations of lead in egg yolks have been found in captive American alligators, suggesting the link between lead exposure and embryo mortality. In addition, the negative impacts of lead on the reproductive success of birds have also been documented.
Lake St Lucia is home to the largest known estuarine crocodile population in Africa. It also contains the largest crocodile nesting population in the country.
Humphries said the continued use of lead is a conservation and sustainability issue. “Globally, there is a growing effort to move away from the use of guided fishing gear to mitigate risks to wildlife and human health,” he said. Humphries believes that the country’s conservation authorities should lead such movements.
For example, in the United States there are restrictions that have led to the reduction of lead exposure in predatory birds such as the California condor.
A newspaper of 2019, The regulation of lead fishing weights involves the recovery of the mute swan population, shows how regulations imposed on lead fishing weights used in recreational fishing in Britain have seen an increase in the size of the Mute Swan population over 39 years. “The percentage of people who die from lead poisoning has abandoned the following regulation,” the document reads.
The document encourages restrictions on the use of toxic substances as a storage medium.
The Department of Forests, Fisheries and the Environment has not yet responded to Fin24’s request for comment.