Cocaine Sharks: What the Studies Mean

M.A. Dworkin

The Caribbean - Sharks off the coast of Brazil have tested positive for cocaine, according to a study published in Science of the Total Environment by marine biologists from the Instituto Oswaldo Cruz (IOC), based in Rio de Janeiro. Also, a more recent study by Environmental Pollution, an international peer-reviewed journal, confirms the findings in a report titled, "Drugs in Paradise: Caffeine, Cocaine, and Painkillers detected in sharks from the Bahamas,

The discovery was made when the scientists collected samples from 13 Brazilian Sharpnose Sharks (Rhizoprionodon lalandii) that had been landed by local fishing vessels. 

A relatively small shark reaching a maximum of just 77cm in length , the Brazilian Sharpnose shark is a coastal dwelling species, making it an ideal candidate to be tested for the presence of chemicals in the water.  

The sharks were dissected and their muscle and liver tissues were tested using a process known as liquid chromatography-tandem mass spectrometry, an analytical system used to separate and detect specific chemical compounds within a sample. 

All of the sharks in the Brazil study tested positive for cocaine and 12 tested positive for benzoylecgonine, a chemical produced in the liver during the metabolism of cocaine, meaning the sharks had consumed the drug. In the Bahamas study, 28 sharks carried measurable levels of human-derived compounds.

The study is reminiscent of the 2023 Discovery Channel documentary ‘Cocaine Sharks’, which explored if sharks off the coast of Florida had been affected by eating bales of drugs dumped into the water by smugglers. The documentary only showcased erratic behavior as a possible result of cocaine consumption, however, and no sharks were tested for the presence of the drug. The Environmental Pollution study did not show any evidence that the sharks were drugged, or behaving erratically. The study does not suggest altered aggression, unusual behavior, or anything that would change how divers should approach these animals. 

The authors of the Brazil study say erratic behavior is a possibility in the sharks they tested, but an unlikely one, as bales of dumped narcotics are not a regular occurrence in the waters off Brazil. The scientists believe it is more likely that the sharks have been exposed to cocaine in human urine and feces found in sewage outflows or drainage from illegal drug laboratories. 

Whether or not the cocaine affected the sharks behavior, or health, was not determined by the Brazil study, however, previous research in the Bay of Santos in Sao Paulo found that cocaine is toxic to mussels, oysters and eels. And the power point in the Bahamas study is that the Bahamas is not an industrial coastline. It is one of the most recognizable dive sites in the world, often marketed on the strength of its water quality and marine life. Finding these compounds in apex predators there suggests the issue is far more widespread than many assume.

Sharks sit at the top of the food chain. When they carry contaminants it is rarely an isolated issue. It suggests those substances are already moving through the ecosystem, from smaller organisms upwards. The long-term effects are still being studied, but early research in marine science has already linked pharmaceutical exposure in other species to changes in behavior and physiology.

Concerns have also been raised that the drug may affect sharks’ eyesight, affecting their ability to hunt; and also contaminate the yolk of their eggs and inhibit reproduction. 

Although there is no definitive proof cocaine makes sharks more aggressive, given this is a well-known effect of cocaine in humans and other animals, the Brazilian report’s authors noted this is a possibility requiring further study.  

Studies related to the presence of illicit narcotics in the water are limited, but increasingly show that drugs - both legal and illegal - are impacting marine life. A 2022 study by scientists from the University of Florida found a total of 58 different pharmaceuticals present in a sample of 93 fish, including blood pressure medications, antidepressants, antibiotics, pain relievers, antihistamines and opioids.