Pharmaceutical pollution alters Salmon migration, study finds

Salmon are known for their remarkable life journey, beginning in freshwater streams and rivers, where they hatch, and continuing with a long migration to the ocean. This transition from freshwater to saltwater is crucial to their development into mature adults and has been shaped over millions of years. However, in the modern age, salmon are encountering a new, human-made challenge: pharmaceutical pollution of their inhabited waterways, which is now affecting their behavior in unexpected ways.

A study published in the journal Science has revealed that exposure to a drug called clobazam, commonly found in wastewater, can influence salmon migration patterns. Clobazam is a benzodiazepine, a class of medications used in humans to treat conditions like epilepsy, anxiety, and sleep disorders. It works by depressing the central nervous system. Because fish share similar neural and physiological structures with humans, they are highly susceptible to drugs designed to alter human neurochemistry. This similarity raises concerns about how such substances might interfere with natural fish behaviors.

The recent research showed that juvenile salmon with clobazam in their systems migrated to the ocean faster and were more adept at navigating obstacles like dams. At first glance, these effects might appear beneficial, helping fish overcome man-made barriers more efficiently. However, scientists caution against this interpretation. Any human-induced alteration in animal behavior, especially via psychoactive substances, is cause for concern. The long-term impacts on salmon’s health, reproductive success, and overall population dynamics remain unknown.

Dr. Christopher C. Caudill, a professor of fish and wildlife sciences at the University of Idaho who was not involved in the study, emphasized in an interview to the CNN the biological similarities between humans and fish. He explained that due to shared anatomical and physiological traits, it's expected that drugs affecting the human brain can also affect fish behavior. This insight deepens the concern about the presence of pharmaceuticals like clobazam in aquatic environments.

While earlier studies had suggested that benzodiazepines could alter salmon behavior, they were largely conducted in artificial laboratory settings and used drug concentrations much higher than what fish would typically encounter in nature. In contrast, the recent study took a more realistic approach. Researchers tracked the full river-to-sea migration of wild juvenile salmon in their natural environment, using clobazam levels that mirrored real-world environmental exposures.

Dr. Marcus Michelangeli, a coauthor of the study from Griffith University in Australia, highlighted this methodological difference. He explained to the publication that their work provides a clearer picture of how actual environmental drug exposure affects wild salmon over their entire migratory path.

The findings underscore a broader ecological issue: pharmaceutical pollution is an emerging threat to wildlife globally. As more drugs enter waterways through wastewater, the unintended consequences on ecosystems may intensify. This research serves as a warning that substances designed for human use can ripple through the environment, disrupting the behaviors and lifecycles of non-human species in subtle yet potentially harmful ways.

By Nazrin Sadigova