A new study by marine scientists has found sharks swimming off a remote island in the Caribbean are testing positive for painkillers, caffeine and even cocaine. The alarming results were picked up by a team from the Federal University of Paraná, Brazil, who were working in waters around the stunning former British colonial territory of The Bahamas.

The islands, which still have King Charles III as their head of state, are known as a tropical paradise and playground of the rich and famous. But worryingly it appears the pristine waters surrounding the archipelago are showing signs of excess that could be a dangerous indicator of man-made pollution.

Working off the coast of Eleuthera Island in The Bahamas, the scientists tested 85 sharks swimming in waters roughly four miles offshore. Incredibly, they discovered that around 30 animals showed traces of caffeine and painkillers, and some of the predators tested positive for multiple over-the-counter drugs. In one case, a shark tested by the team even showed traces of cocaine in its system.

The study "Drugs in paradise: caffeine, cocaine, and painkillers detected in sharks from The Bahamas" has now been published in the Science Direct journal.

Natascha Wosnick, a biologist with the Federal University of Paraná, said the waters where the sharks were swimming were close to fish farms where divers would operate and near to sewage outflow pipes.

She told ScienceNews she believed the results were "mostly because people are going there, peeing in the water and dumping their sewage in the water".

She added that the sharks "bite things to investigate and end up exposed" to substances, but the high proportion of results in the sample was worrying because "we're talking about a very remote island in The Bahamas".

The study reports that 28 sharks showed signs of substances, including acetaminophen and diclofenac, which are active ingredients in anti-inflammatory drugs.

In the published report it was noted: "To the best of our knowledge, this is the first report of caffeine and acetaminophen detected in any shark species worldwide, and the first report of diclofenac and cocaine in sharks from The Bahamas."

The scientists found the sharks with substances in their blood showed signs of different metabolic markers, with those exposed to to caffeine showing more movement and reaction, similar to the effect on humans.

Tracy Fanara, an oceanographer at the University of Florida in Gainesville, told ScienceNews: "What makes this study notable is not just the detection of pharmaceuticals and cocaine in nearshore sharks, but the associated shifts in metabolic markers."