PCB Accumulation by Salmonine Smolts and Adults in Lake Michigan and its Tributaries and its Effect on Stocking Policies

Abstract

In 1987, the Wisconsin Department of Natural Resources suspended stocking of salmonines in the Sheboygan River, a Lake Michigan tributary in southeastern Wisconsin and an Environment Protection Agency Superfund site, because of contamination with polychlorinated biphenyls (PCBs). Starting in 1990, uniquely finclipped, hatchery-raised fish were stocked in the Sheboygan River and two other Lake Michigan tributaries (Pigeon and Root rivers) to determine whether PCB accumulation in salmonine species warranted a continued ban on stocking fish into that system. Smolts were collected, homogenized, and analyzed (whole-body) monthly until they migrated from the river. Skin-on fillets and whole-body PCB analyses were performed on returning sub-adults and adults. To determine levels of PCB contamination in stocked salmonines, we (1) measured PCB levels in rainbow trout Oncorhyncus mykiss and coho salmon O. kisutch smolts stocked in the Sheboygan River and compared these data with comparable data from two reference locations; (2) measured PCB levels in returning adult rainbow trout and coho salmon after residence in Lake Michigan; and (3) made recommendations regarding future salmonine stocking policy for the Sheboygan River. Sheboygan River smolts stocked in the fall accumulated higher PCB concentrations than smolts stocked in other rivers and those stocked in the spring. Total PCB concentrations in skin-on fillets of sub-adult and adult coho salmon and sub-adult and adult rainbow trout from the Sheboygan River did not differ significantly from concentrations in sub-adults and adults returning to reference rivers. Returning sub-adult and adult fillet samples did not exceed the U.S. Food and Drug Administration tolerance level for PCBs of 2.0 /μg/g wet weight. Results indicated that PCB concentrations in smolts were not correlated with PCBs concentrations in adult skin-on fillet samples. Therefore, we recommended the Sheboygan River be stocked with chinook salmon O. tshawytscha, coho salmon, and rainbow trout.