Sharks found in waters off Brazil have tested positive for cocaine prompting fears the drug could potentially be affecting their behaviour.
The illicit drug has widely been detected in aquatic ecosystems, but its presence in free-ranging sharks is not thought to have previously been tested.
A new study examined 13 Brazilian sharpnose sharks, taken aboard by small fishing boats, and found every one of them tested positive for cocaine.
The drug was found in the sharks’ muscle and livers, while 92 per cent also tested positive for cocaine’s main metabolite, benzoylecgonine.
Sara Novais, a marine ecotoxicologist at the Marine and Environmental Sciences Centre of the Polytechnic University of Leiria, told Science the findings are “very important and potentially worrying”.
Dr Enrico Mendes Saggioro, also an ecotoxicologist at the Oswaldo Cruz Institute, told The Telegraph the cocaine could be affecting sharks’ behaviour.
“Cocaine targets the brain, and hyperactive and erratic behaviour has been noted in other animals,” he said. “It’s a possibility and further studies are required.”
There are also fears cocaine could reduce the life expectancy of sharks.
How the animals came to ingest the cocaine is not known, but it is thought the drug has been leaked into Brazil’s water system through human waste, and through drains from illegal laboratories.
Cocaine has been found in seas and water systems around the world, including in the waters off England’s south coast, and in London’s sewage system.
Dr Rachel Ann Hauser-Davis, a British scientist and member of the research team from the Oswaldo Cruz Foundation in Rio de Janeiro, told The Telegraph the study showed “chronic exposure due to human use of cocaine in Rio de Janeiro and the discharge of human urine and faeces by sewage outfalls, as well as from illegal labs”.
Sharks feed on other fish, meaning they could build up higher levels of cocaine and other pollutants than creatures further down the food chain.
Dr Hauser-Davis dismissed another theory, that the apex predators could have been feeding on bricks of cocaine dumped at sea by drug smugglers.
In 2023, Discovery Channel documentary Cocaine Sharks explored rumours that sharks were feeding on bales of cocaine jettisoned in the waters off Florida.
“We don’t usually see many bales of coke dumped or lost at sea here [in Brazil], unlike in Mexico and Florida,” Dr Hauser-Davis told The Telegraph.
The findings were published in journal Science of the Total Environment.
The paper’s co-authors pointed out that sharks are eaten as food in Brazil, high levels of cocaine in the animals could potentially pose a risk to humans.
