Sharks testing positive for cocaine found in waters off Brazil

2023 was a notable year for the concept of "sharks on coke." It began with the release of "Cocaine Shark," a B-movie featuring mutant, murderous sharks (which, ironically, never actually encountered the drug). A few months later, a more serious documentary titled "Cocaine Sharks" was released, investigating whether sharks in the Gulf of Mexico consume the many packages of cocaine lost or dumped by drug smugglers.

Tracy Fanara, a science communicator with the National Oceanic and Atmospheric Administration (NOAA), told The Guardian last year, “It’s a catchy headline to shed light on a real problem.” Fanara, who participated in the documentary, emphasized the issue of wildlife being exposed to drugs and other pollutants. However, the documentary found inconclusive evidence of sharks consuming cocaine.

Sharpnose sharks, like this one, have tested positive for cocaine near Rio de Janeiro.

Recently, scientists in Brazil have reported the first evidence that sharks are indeed exposed to cocaine. Researchers reported in the journal Science of the Total Environment that 13 sharpnose sharks from coastal waters near Rio de Janeiro had traces of the drug in their muscles and livers.

Sara Novais, a marine ecotoxicologist at the Marine and Environmental Sciences Centre of the Polytechnic University of Leiria, commented that the findings are "very important and potentially worrying." Although she was not involved in the study, she stressed the need for more research to determine if the sharks—or the humans who consume them—are harmed by the exposure.

Cocaine has been detected in sewage and rivers in various countries, including Brazil. Around Rio de Janeiro, the drug likely enters the sea directly from drainage linked to illegal labs where cocaine is refined, as well as from drug users via untreated sewage. Cocaine packs lost or dumped by traffickers might also contribute to this pollution.

Enrico Mendes Saggioro, an ecotoxicologist with the Oswaldo Cruz Institute, and his colleagues sought to determine if sharks might be exposed to cocaine. Brazilian sharpnose sharks (Rhizoprionodon lalandii), which live their entire lives in coastal waters, seemed likely candidates for such exposure, either directly from seawater, from consuming contaminated fish, or from ingesting drifting packages. Unlike the large, fearsome sharks featured in "Cocaine Sharks"—great hammerheads, tiger sharks, and other large species—the Brazilian sharks studied were juveniles and small adults, averaging 52 centimeters in length and weighing less than a quart of milk.

The research team acquired 13 sharks from small fishing vessels targeting this species and others. In the lab, they dissected the sharks and tested muscle and liver tissues using liquid chromatography with tandem mass spectrometry. All samples tested positive, with concentrations up to 100 times higher than previously reported for other aquatic creatures.

Floating packages of cocaine could be a source of drug contamination of sharks, but polluted water may be a more likely source.New Zealand Defense/ZUMA via Alamy

Anna Capaldo, an endocrinologist and environmental pollution expert at the University of Naples Federico II, who did not participate in the research, stated, “This is evidence of the increasing danger of cocaine pollution.”

One concern is that toxicants in the sharks’ livers could hinder the production of vitellogenin, essential for egg yolk formation. All females in the study were pregnant, though the impact of cocaine exposure on the fetuses is unknown. Additionally, it remains unclear whether the drug affects shark behavior.

Cocaine can be toxic to mollusks, crustaceans, and bony fish. Previous lab studies have shown that environmentally realistic concentrations can cause DNA fragmentation and cell death in zebrafish embryos and disrupt important hormones in eels. However, only a few studies have tested wild fish for illegal narcotics.

Saggioro and his co-authors advocate for more testing for cocaine in coastal waters to pinpoint its sources. As apex predators consuming fish across wide areas, sharks could serve as indicators of hotspots of illegal drug pollution. The team also notes that sharks are a common food source in Brazil and, if highly contaminated with cocaine, could pose a health risk to humans.

If you would like to write for The Daily Jaws, please visit our ‘work with us’ page

For all the latest Jaws, shark and shark movie news, follow The Daily Jaws on Instagram, Twitter and Facebook.