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Health of white sucker within the St. Louis River area of concern associated with habitat usage as assessed using stable isotopes
Citation:
Blazer, V., J. Hoffman, H. Walsh, R. Braham, C. Hahn, P. Collins, Z. Jorgenson, AND T. Ledder. Health of white sucker within the St. Louis River area of concern associated with habitat usage as assessed using stable isotopes. Ecotoxicology. Springer, New York, NY, 23(2):236-251, (2014).
Impact/Purpose:
The goal of this study was to test the utility of integrating stable isotope-based habitat information with ecotoxicological biomarkers in fish for assessing habitat-related exposure to contaminated sediments. Stable isotopes are a diet marker; where the stable isotope composition of the food web varies between habitats (e.g., a river and a lake), it can be used to track feeding between the two locations. We collected 200 adult white sucker (Catostomus commersoni), a demersal fish, from across the St. Louis River Area of Concern (AOC) in spring 2011. Overall, the incidence of raised skin lesions was high (31%) and the incidence of skin and liver tumors (neoplasia) was relatively low (4.5%). Stable isotope-based measures of habitat were useful in two different ways. First, stable isotope ratios of white sucker indicated most had been feeding largely within the AOC over the past 1-2 years, indicating they were resident in the AOC and not Lake Superior. Second, the amount of diet obtained from the upper estuary was a significant predictor of skin lesion incidence. Hence, habitat use within the AOC appears to be an important risk factor for skin and possibly, liver lesions. We conclude that the stable isotope-based approach demonstrates some promise for relating habitat-based exposure to contamination to ecotoxicological effects in aquatic species.
Description:
In Spring 2011, 200 adult white sucker were collected in four areas of the St. Louis River Area of Concern (AOC), located in Minnesota and Wisconsin, USA. The areas included the upper AOC as a reference area, the upper estuary, St. Louis Bay and Superior Bay. Grossly visible abnormalities were documented and preserved for microscopic analyses, as were five to eight representative pieces of liver tissue. A piece of dorsal muscle was preserved for stable isotope analyses and otoliths removed for age determination. The incidence of raised skin lesions (mucoid plaques) was high (31%), however, microscopically only 4.5% of the white suckers had neoplasia (papillomas). The remaining lesions were epidermal hyperplasia. Superior Bay had the lowest percentage of skin/lip lesions (10%), while St. Louis Bay had the highest (44%). St. Louis Bay also had the highest incidence of skin neoplasms (12%). No hepatocellular neoplasms were documented, however bile duct tumors were observed in 4.5% of the suckers. Foci of cellular alteration were observed in fish from all sites except the upper AOC. Stable isotope data indicated that most of the suckers relied on the St. Louis River AOC for the majority (>75%) of their diet, indicating they were resident within the AOC and not in Lake Superior. The amount of diet obtained from the upper estuary was a significant predictor of skin lesion incidence. Hence, habitat use within the AOC appears to be an important risk factor for skin and possibly, liver lesio
