Cocaine Pollution May be Changing How Far Atlantic Salmon Swim — with Potential Ecosystem Effects
Atlantic salmon are born in freshwater rivers, migrate to the ocean, and then return with unerring accuracy to their spawning rivers to breed. All that travel is tiring, but it appears some of these fish may be swimming further from an unusual source.
Researchers have studied the effect of cocaine pollution on wild salmon for the first time in a paper published in Current Biology. The researchers used implants that slowly released cocaine or its main metabolite into their salmon’s bodies, along with telemetry devices that tracked the fish’s movements over two months.
“The idea of cocaine affecting fish might seem surprising, but the reality is that wildlife is already being exposed to a wide range of human-derived drugs every day,” said Marcus Michelangeli, an environmental scientist at Griffith University and co-author of the new paper, in a statement. “The unusual part is not the experiment, it’s what’s already happening in our waterways.”
Salmon and Cocaine Pollution
Cocaine pollution is increasing in our waterways, but previous work had only studied the drug’s impact on fish in laboratory settings.
The study found, perhaps unsurprisingly, that fish on cocaine and its metabolite swam further than unexposed fish. The authors say that the findings matter because anything that changes how salmon move and migrate will impact their ecosystem.
“Where fish go determines what they eat, what eats them, and how populations are structured,” said Michelangeli. “If pollution is changing these patterns, it has the potential to affect ecosystems in ways we are only beginning to understand.
Read More: Caffeine, Cocaine, and Painkillers Found in Sharks in the Bahamas — A Sign of Human Pollution Reaching Marine Predators
Increasing the Salmon’s Swimming
Michelangeli and his team studied a group of 105 salmon over eight weeks that migrated to and from Lake Vättern, Sweden’s second-largest lake. The team divided their fish into three groups: a control group not exposed to any chemicals, a group exposed to cocaine, and a third group exposed to a compound called benzoylecgonine, a cocaine metabolite frequently found in wastewater samples.
All three fish groups decreased their movement over the eight weeks of the study as their overall activity declined. But by the end of the study, fish exposed to cocaine or benzoylegonine were more active than the control fish.
In the study’s final two weeks, fish dosed with cocaine swam roughly 3 miles (5 kilometers) more than control fish, and those dosed with benzoylegonine swam nearly 8 miles (14 kilometers) more — nearly double the distance.
The drugs also changed the fish’s migration routes. Unexposed fish stuck to the lake’s southern portion, while cocaine- and metabolite-dosed fish moved north. By the final weeks of the study, benzoylegonine-exposed fish had traveled more than 7 miles (roughly 12 kilometers) farther away from their release site than control fish.
Cocaine Pollution Effects
The finding that benzoylegonine had a stronger effect on movement than cocaine itself is important because risk assessments focus more on cocaine than its metabolites, even though the latter are more common in waterways.
There’s likely no risk of this chemical adventure impacting people who snack on salmon, according to the study authors. The levels of cocaine they dosed the salmon with reflected levels already present in waterways, and the compounds decay over time.
The researchers now plan to determine how significant this type of pollution is in our waterways and whether cocaine affects salmon’s reproduction or lifespan.
Read More: Are Sharks Ingesting Bales of Cocaine and Other Pollutants?
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