Conservation Benefits of Lake Outlet Dam Removals: Reduced Mercury in an Apex Fish Predator

ABSTRACT Biomagnification of environmental toxins is influenced by food chain length, which in turn is shaped by habitat connectivity and food web dynamics. Dam removals are increasingly used as restoration measures, yet their role in reducing contaminant exposure has rarely been quantified. We tested if mercury concentration in pike ( Esox lucius ) muscle tissue was reduced by removals of lake outlet dams in five oligotrophic, boreal lakes, using a before‐after design. For pike of average size (50 cm), mean mercury concentration decreased from 843 to 598 μg Hg per kg muscle tissue following dam removal, which corresponds to a 29% reduction. These results show that dam removal can lower mercury bioaccumulation in apex predators, providing an additional conservation benefit of restoring natural aquatic connectivity, with positive implications for both ecosystem integrity and human health.