'Cocaine sharks' discovery sparks fears over potential dangers of drug-induced 'erratic' behaviour

Sharks might be getting high on cocaine dumped in the ocean, scientists fear . The shocking revelation comes as shark attacks are on the rise , with experts suggesting that sharks could be ingesting the drug from illegal drug labs chucking their chemical waste into the sea or from sewage polluted by users' excretions.

Researchers reckon the most likely source is the ocean being contaminated with cocaine through sewage tainted by drug users. Rachel Ann Hauser-Davis, a British researcher at the Oswaldo Cruz Foundation in Rio de Janeiro, revealed the findings show "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".

The study involved 13 Brazilian sharpnose sharks caught by local fishers off the coast of Rio. Tests showed each shark had worryingly high levels of cocaine in their systems .

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The study, published in the journal Science of the Total Environment, suggested that sharks exposed to cocaine might be becoming more aggressive due to the effects of the addictive substance.

"Cocaine targets the brain, and hyperactive and erratic behaviour has been noted in other animals. It's a possibility and further studies are required," explained Dr Enrico Mendes Saggioro, an ecotoxicologist from the Oswaldo Cruz Institute.

The shark species was chosen for the study because of its lifelong habitation in coastal waters, where traces of cocaine are believed to be most concentrated. Shockingly, researchers found cocaine concentrations up to 100 times higher than previously discovered in other marine creatures in the sharks' muscles and livers.

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While there's currently little evidence to suggest that the drug is causing the sharks to go into wild frenzies, it could have long-term effects on their health, warns one expert. Dr Tracy Fanara, a specialist in ecotoxicology and environmental engineering from the University of Florida , suggested that it might affect the sharks' growth rates and breeding levels.

"They may not be going nuts from the cocaine but it could reduce their life expectancy," she shared with the Telegraph. She has called for more research into how man-made chemicals influence ecosystems and impact animals both on land and sea.