Traces of cocaine present in freshwater are drastically altering the behavior of wild salmon, driving them to swim farther and disperse over much greater distances than normal. This is the finding of a major international study, the first to document these effects directly in nature, published in the prestigious journal "Current Biology." The research was led by Griffith University in Australia, in collaboration with scientific institutions from Sweden, Germany, and the Zoological Society of London.
To analyze this phenomenon outside controlled laboratory conditions, researchers monitored 105 young Atlantic salmon for eight weeks in Sweden's Lake Vattern. Using slow-release chemical implants and advanced telemetry technology, the fish were divided into three groups: a control group, a group exposed to cocaine, and a group exposed to benzoylecgonine, which is the primary metabolite of cocaine regularly found in urban wastewater.
The results were startling; fish exposed to benzoylecgonine swam up to 1.9 times more during a week compared to those unaffected by the pollution. Furthermore, these salmon dispersed up to 12.3 kilometers farther within the lake. Scientists noted that these changes became more pronounced over time, indicating that continuous exposure fundamentally alters how fish utilize space in the ecosystem.
Researcher Marcus Michelangeli from Griffith University explains that the location of fish determines everything; from what they eat to the predators that hunt them. If pollution is changing these movement patterns, the entire ecosystem could be affected in ways that science is only beginning to understand. A key finding of the study was that the cocaine metabolite had a stronger effect than the drug itself, suggesting that biological risks in rivers and lakes may have been underestimated until now, as assessments typically focus on the base substance.