Drug pollution alters migration behavior in salmon
Griffith University
image:
Dr Marcus Michelangeli conducting the field study in Sweden’s River Dal.
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In the largest study of its kind to date, a team of international researchers has investigated how pharmaceutical pollution affects the behaviour and migration of Atlantic salmon.
The study, led by the Swedish University of Agricultural Sciences, revealed that commonly detected environmental levels of clobazam – a medication often prescribed for sleep disorders – increased the river-to-sea migration success of juvenile salmon in the wild.
The researchers also discovered that clobazam shortened the time it took for juvenile salmon to navigate through two hydropower dams along their migration route – obstacles that typically hinder successful migration.
Dr Marcus Michelangeli from Griffith University's Australian Rivers Institute, who was a key contributor to the study published in Science, emphasised the increasing threat of pharmaceutical pollution to wildlife and ecosystems worldwide.
“Pharmaceutical pollutants are an emerging global issue, with over 900 different substances having now been detected in waterways around the world,” Dr Michelangeli said.
“Of particular concern are psychoactive substances like antidepressants and pain medications, which can significantly interfere with wildlife brain function and behaviour.
Dr Michelangeli noted that the study’s real-world focus sets it apart from previous research.
“Most previous studies examining the effects of pharmaceutical pollutants on wildlife have been conducted under controlled laboratory conditions, which don’t fully capture the complexities of natural environments,” he said.
“This study is unique because it investigates the effects of these contaminants on wildlife directly in the field, allowing us to better understand how exposure impacts wildlife behaviour and migration in a natural context.
“While the increased migration success in salmon exposed to clobazam might seem like a beneficial effect, it is important to realise that any change to the natural behaviour and ecology of a species is expected to have broader negative consequences both for that species and the surrounding wildlife community.”
The research team employed innovative slow-release pharmaceutical implants and animal-tracking transmitters to monitor how exposure to clobazam and the opioid painkiller tramadol – another common pharmaceutical pollutant – affected the behaviour and migration of juvenile Atlantic salmon (Salmo salar) in Sweden’s River Dal as they migrated to the Baltic Sea.
A follow-up laboratory experiment also found that clobazam altered shoaling behaviour, indicating that the observed migration changes in the wild may result from drug-induced shifts in social dynamics and risk-taking behaviour.
Dr Michelangeli explained that predicting the full extent of these impacts remains challenging
“When you consider realistic exposure scenarios where entire ecosystems are exposed – encompassing multiple species and a diversity of contaminants – the potential consequences become even more complex,” he said.
While the recent decline of Atlantic salmon is primarily attributed to overfishing, habitat loss, and fragmentation – leading to their endangered status – the study highlights how pharmaceutical pollution could also influence key life-history events in migratory fish.
Dr Michelangeli pointed out that many pharmaceuticals persist in the environment due to poor biodegradability and insufficient wastewater treatment. However, there is hope.
“Advanced wastewater treatment methods are becoming more effective at reducing pharmaceutical contamination, and there is promising potential in green chemistry approaches,” he said.
“By designing drugs that break down more rapidly or become less harmful after use, we can significantly mitigate the environmental impact of pharmaceutical pollution in the future.”
The study ‘Pharmaceutical pollution influences river-to-sea migration in Atlantic salmon (Salmo salar)’ has been published in Science.
In-lab demo of altered migrati [VIDEO] |
An in-lab demonstration of the impacts pharmaceuitcal pollution is having on Atlantic salmon migration behaviou
Journal
Science
Article Title
Pharmaceutical pollution influences river-to-sea migration in Atlantic salmon (Salmo salar)
Psychoactive pharmaceutical pollution alters migration behavior in wild salmon
Summary author: Walter Beckwith
Widely detected in global waterways, clobazam – a common drug used to treat anxiety – is altering the migration behavior of wild Atlantic salmon, according to a new study. The findings underscore the far-reaching ecological consequences of pharmaceutical pollutants, revealing how even trace levels of psychoactive drugs can disrupt essential survival behaviors in wildlife. Pharmaceutical pollution – particularly in waterways – is a growing environmental concern that poses a serious threat to biodiversity, ecosystem functioning, and public health. More than 900 active pharmaceutical or pharmaceutical-derived compounds have now been detected in waterbodies across the globe, including Antarctica. These contaminants, designed to target conserved neurobiological pathways and remain effective at low concentrations, persist in the environment, and even trace amounts of psychoactive pharmaceuticals, such as antidepressants and anxiolytics, have been shown to alter animal behavior by acting on neural pathways. While laboratory studies shed light on behavioral effects, they often fail to capture the complexity of natural ecosystems, leaving ecological impacts uncertain. Through laboratory assays and multi-year field experiments, Jack Brand and colleagues investigated the impact of psychoactive pharmaceutical pollutants on the behavior of Atlantic salmon. Brand et al. discovered that the anxiolytic drug clobazam – a common pharmaceutical pollutant – accumulated in the brains of exposed salmon, altering their ability to navigate dam passages and overall river-to-sea migration success. Specifically, the findings revealed that clobazam exposure increased the number of salmon smolts reaching the sea, likely due to heightened risk-taking and reduced shoaling (grouping) behavior. While there were no significant differences in overall migration speed, exposed smolts moved through hydropower dams more quickly, suggesting that increased risk-taking behavior facilitated barrier navigation. However, lab experiments revealed that clobazam also reduced shoaling cohesion, particularly in the presence of predators, which could heighten predation risk in the wild. According to the authors, the findings highlight the complex ecological consequences of pharmaceutical pollution, as behavioral changes induced by psychoactive drugs may both aid migration and increase vulnerability to natural threats.
“Our findings raise important questions about how pharmaceutical pollution alters migration behavior and survival in the wild,” said Brand. “Next, we aim to track fine-scale movements of exposed fish using high-resolution animal tracking tools and miniature biologgers – tiny electronic tags that record physiological data such as stress levels or detect predation events – to determine whether behavioral changes from pharmaceutical pollution influences predation risk. Expanding our understanding of how different psychoactive pollutants and their interactions affect migration success will be crucial for predicting the long-term impacts on fish populations. This is especially important in an increasingly polluted world, where evidence-based policies are needed to protect vulnerable species and ecosystems.”
Journal
Science
Article Title
Pharmaceutical pollution influences river-to-sea migration in Atlantic salmon (Salmo salar)
Article Publication Date
11-Apr-2025
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