PCB concentrations in walleyes and their prey from the Saginaw River, Lake Huron: A comparison between 1990 and 2007

Concentrations of polychlorinated biphenyls (PCBs) were measured in composited samples of walleyes Sander vitreus and their prey during 2005-2007 from Saginaw Bay, Lake Huron. There was a linear relationship between fish length and PCB concentrations in walleyes between 356 and 608 mm, but fish 680 mm had lesser concentrations than 608-mm fish. When fish 222-550 mm from 1990 were compared with those from 2007, there was a decrease of 1315 ng PCBs/g wet wt (ww). Concentrations of PCBs in gizzard shad Dorosoma cepedianum (190 ng PCBs/g ww) were three-fold less than fish collected in 1990 (516 ng PCBs/g ww). Round gobies Neogobius melanostomus collected from the Saginaw River had the greatest concentrations of PCBs (range: 200-350 ng PCBs/g ww) compared with other prey fishes (45-190 ng PCBs/g ww). Concentrations of PCBs in Saginaw River round gobies were three-fold greater than those from Saginaw Bay. Zooplankton from 1990 and 2008 contained 8.0 and 32 ng PCBs/g ww, respectively, while zebra mussels Dreissena polymorpha from 2008 contained 351 ng PCBs/g ww. Principal components analysis showed that PCB congeners differed between the largest walleyes and other fish. There are several possible explanations for lesser concentrations of PCBs observed in 2007. These include effects of dredging, changes in the food web related to round gobies, loss of alewife Alosa pseudoharengus, which was a major walleye prey item in 1990, and replacement by yellow perch Perca flavescens, or decreases in release of PCBs from sediments due to weathering, burial, or diffusion.