Scientists are calling for all lead fishing tackle to be banned around Lake St Lucia after finding crocodiles with the highest levels of lead poisoning in the world – some now losing their teeth or showing signs of anemia .
Saint Lucia, part of the iSimangaliso Wetlands Park and World Heritage Site, is home to around 1,000 crocodiles. It is one of the few remaining breeding populations of Nile crocodiles in the country and the largest estuarine population in Africa.
Dr Marc Humphries, lead author of a study published in the journal Chemosphere, said lead was found in the blood of every crocodile tested at the lake, with concentrations ranging between 86 and 13,100 ng/mL (nanograms per milliliter). These were the highest concentrations reported for crocodiles worldwide.
Although most reptiles appeared to be in good physical condition, those most poisoned had four to five times fewer red blood cells than ‘normal’ crocodiles – and severe tooth decay.
“These results suggest that anemia and tooth loss may be clinical signs of long-term environmental exposure to lead,” said Humphries, senior lecturer and associate professor in the University’s School of Chemistry. of Witwatersrand.
Although not previously documented in crocodiles, alligators, or caimans, these symptoms were also consistent with similar lead poisoning seen in birds and mammals elsewhere in the world.
This suggests that crocodilians may be more susceptible to the long-term toxic effects of lead than previously thought.
Call for an “immediate” ban
Widespread accidental exposure of many forms of wildlife to this toxic metal – through lead fishing weights, shotgun pellets and other lead-based ammunition – is now a major global concern because lead is an accumulative metabolic poison.
Because it poisons the brain and nervous system, lead has been banned from gasoline and paint to protect human health.
Several studies have also linked exposure to neuropsychiatric disorders such as attention deficit disorder, learning disabilities and higher levels of criminality.
Now Humphries and his research colleagues are calling for an immediate ban on fishing sinkers around Lake St. Lucie.
“South Africa introduced regulations eliminating lead from petrol nearly two decades ago, but we still allow its use in some of our most important conservation areas,” he said. Our burning planet.
“On the surface, this looks pretty weird, but I think lack of awareness is one of the main issues. In my opinion, iSimangaliso should ban the use of lead immediately.
The iSimangaliso Wetlands Park Authority said it would study the report and consider its implications “in line with our adaptive management approach”.
Although lead weights do not rust and have the advantage of being heavy and easy to melt and mold, Humphries says steel and tungsten are among the most popular non-toxic alternatives internationally.
Why are crocodiles poisoned?
One of the main reasons crocodiles are so vulnerable is that they deliberately swallow small stones and pebbles (gastroliths) to help crunch food through their digestive tract.
Autopsies have revealed that some crocodiles swallow lead sinkers to serve as gastroliths, while others sometimes snatch fish snagged by fishermen at Lake St. Lucie.
Humphries and colleagues Xander Combrink, Jan Myburgh, and Robert Campbell note that several waterfowl and other seed-eating birds also swallow gravel and pebbles to aid digestion.
Unfortunately, lead fishing weights remain in the stomach because the small pyloric valve of a crocodile’s stomach prevents these objects from passing into the duodenum and being excreted as waste.
These pieces of lead can be retained and slowly dissolved in the crocodilian’s stomach for years or even decades. When it dissolves in stomach acids, lead is absorbed into the blood, body tissues and bones.
St. Lucia’s crocodiles appear particularly vulnerable because the 70 km long estuarine lake sits on a sandy coastal plain characterized by muddy sediments with few pebbles. It is therefore possible that they actively target pellets to serve as gastroliths.
read in Daily Maverick: “Lake St. Lucia Fishermen – “We just want to fish. Why are they killing us?”
The vast majority of the breeding population is found in the aptly named Narrows section of Lake St. Lucie.
Although crocodiles feed on a variety of mammals, including antelope, bushpig, and hippopotamus, the diet of adult Lake St. Lucia crocodiles consists primarily of fish.
Humphries believes crocodiles have been exposed to poisoned lead since recreational fishing began on Lake St. Lucie in the 1930s and 1940s.
Given that some of the large male crocodiles are now over 50 years old, it is likely that they have had prolonged exposure to lead, with large volumes accumulating in their bones.
Other studies show that prolonged exposure to the metal can lead to significant reductions in the calcium and magnesium content of bones and teeth.
“It appears that lost teeth are not being replaced, and it is possible that long-term damage to supporting bone tissue may prevent new teeth from growing in those affected. In severe cases, tooth loss could therefore lead to nutritional stress and possibly death.
The latest crocodile study also highlighted the wider accidental damage to wildlife caused by hunting and fishing.
In a separate study, English waterfowl researcher Kevin Woods also called for stricter regulation of lead-based ammunition and fishing tackle to reduce wildlife poisoning across the world.
He said poisoning from fishing sinkers and lead ammunition remains a major cause of death in a wide range of wildlife, including the critically endangered California condor as well as the backed vulture. white and Cape vulture endangered in Africa.
In Britain, historical studies have linked the death of 4,000 mute swans each year to the ingestion of lead fishing weights.
A voluntary campaign to reduce and phase out the use of lead among anglers was deemed ineffective and regulations were issued in 1986 to prohibit the importation and supply of lead weights in the sizes deemed most likely to lead. be ingested by swans.
Since the regulation of lead fishing weights, the number of mute swans has increased dramatically, and restrictions on the use of lead shot in North America have been effective in reducing lead poisoning in waterfowl and birds. predators.
Back in South Africa, Humphries said: “At Lake St. Lucia, the case for ending the use of lead in fishing activities is clear… A move towards non-toxic alternatives is warranted and represents the only practical way to mitigate the risk of exposure to wildlife. ” DM168
This story first appeared in our weekly daily maverick 168 newspaper, which is available nationwide for R25.