Potential for contaminant biotransport by migratory fish prior to dam removal and selective fish passage in a Great Lakes tributary

Dam removals and fish passage can enhance aquatic connectivity but may also promote upstream transport of legacy contaminants by migratory fish. This study assessed the potential for contaminant biotransport in Michigan's Boardman River following the planned removal of the Union Street Dam and installation of FishPass, a selective fish passage facility. We quantified polychlorinated biphenyls (PCBs), mercury (Hg), and organochlorine pesticides in carcass and egg samples from migratory species including Chinook and coho salmon, migratory rainbow trout, common white and longnose sucker, lake trout, walleye, and sea lamprey. Chinook salmon exhibited the highest PCB concentrations in both carcasses and eggs, exceeding those of rainbow trout and native suckers. Similarly, Chinook salmon were predicted to deposit up to 2,200 mg PCBs upstream under a high run size scenario, over 80 and 100 times greater than rainbow trout and native suckers. Although suckers had lower individual contaminant burdens, their relatively large run sizes contributed moderately to potential contaminant biotransport compared with rainbow trout, indicating an interaction between abundance and spawner contaminant burden. Stream-resident brook and brown trout in reaches open to migratory fish had higher PCBs and lower Hg concentrations than in closed reaches, likely reflecting dietary exposure to eggs and growth dilution. These results demonstrate that the potential for contaminant biotransport varies widely among migratory species and highlights the need for managers to consider both contaminant burden and run size when making fish passage decisions to balance ecological restoration with contaminant exposure risk.