| In the last decade, it has been discovered that most major rivers and lakes in Sweden, and the entire Baltic Sea, are now contaminated with pharmaceutical pollution (e.g. antidepressants, antibiotics). Despite this, regulation concerning the release of pharmaceutical waste into the environment is still non-existent in Sweden, and many other countries, because legislators lack an understanding of how these contaminants impact aquatic ecosystems. This is very concerning as wildlife are being exposed to dangerous combinations of active drugs that could have unpredictable and long-lasting consequences. For this reason, our research group, led by Prof Tomas Brodin, has spent the last 8 years studying the ecological impacts of drugs in the wild. Our research is world-leading and has revealed previously undetected effects of drug pollution on wildlife behaviour, species demographics, and ecosystem functioning. This includes our recent analysis suggesting that one of Sweden’s most valuable species, the Atlantic salmon (Salmo salar), may be especially vulnerable to the effects of pharmaceutical pollution. We found that Atlantic salmon exposed to environmentally relevant concentrations of pharmaceutical pollutants bioaccumulate these drugs to a high degree in their brain, muscle, and liver tissues. This is alarming as much lower drug concentrations have been shown to compromise ecologically important behaviours in other fish species. In view of these new findings, we outline a series of world-first experiments to investigate the potential for two of Sweden’s most widespread and hazardous pharmaceutical pollutants, clobazam and tramadol, to change the schooling behaviour and migration success of Atlantic salmon. Schooling is an important behavioural process for salmon during their downstream migration to the sea and return migration for breeding. Yet, no research to date, has examined the effects of pharmaceutical pollution on schooling behaviour in salmon, which strongly influences their migration timing, navigation, and success. Such research is crucial for the protection of salmon populations in Sweden, which are already highly threatened and could be at further risk due to the increasing presence of drugs in the environment. We will first conduct a detailed assessment of the independent and combined effects of clobazam and tramadol on the movement and leadership structure of salmon schools using a high-throughput camera and software system in the laboratory. This detailed analysis in the laboratory will then inform a second experiment, which will utilise state-of-the-art animal tracking technology to determine how drug mixtures influence the collective movement, timing, and navigation of salmon during their migration in the wild. In doing so, our project will generate critical new knowledge about how drug mixtures affect our aquatic systems and wildlife. This knowledge will empower regulators to make informed decisions regarding the mitigation and prevention of pharmaceutical pollutants entering the environment. Importantly, our project will also shine a light on emerging issues regarding the conservation of Atlantic salmon populations, and directly addresses Sweden’s National Environmental Quality Objectives (e.g Flourishing Lakes and Streams)
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