Growth and Contaminant Dynamics of Lake Superior Lake Trout

Abstract

Lean lake trout ( Salvelinus namaycush) and the endemic siscowet are ecologically distinct phenotypes of char inhabiting Lake Superior. To examine growth and contaminant concentration dynamics of these fishes, and to assess their utility as indicators of environmental contamination, length, weight, estimated age, and muscle tissue lipid and organochlorine (OC) chemical concentration data were analyzed. Lean lake trout grew faster in length and weight than siscowet. Siscowet muscle tissue lipid concentrations were on average greater than in lean lake trout and increased with length and age, while lean lake trout muscle tissue lipid concentrations decreased in larger, older fish. Polychlorinated biphenyls (PCBs) were the most often detected contaminant, found in 95% of the lean lake trout analyzed and 100% of the siscowets. PCBs attained the highest concentration of the OC compounds quantified, followed by p,p’-DDE, dieldrin, and trans-nonachlor, respectively. Siscowet had greater total concentrations of PCBs at length than lean lake trout, but siscowet and lean lake trout had similar concentrations of PCBs at age. Based on 1990s growth and contaminant data, it is estimated that an 88 cm total length (16-year-old) lean lake trout and a 62 cm total length (15-year-old) siscowet from Lake Superior will exceed the 2.0 mg/kg “Action Level” for total concentrations of PCBs set by the United States Food and Drug Administration. Study results show phenotypic differences in growth and contaminant dynamics between lean lake trout and siscowet, findings that may improve our understanding and management of Lake Superior's aquatic resources.