Ecological impacts of contaminants on population patterns in wild fish are impacted by many contaminants\nthat readily enter aquatic systems. Responses to toxicants by individuals in lab studies\ngenerally do not predict population level consequences in natural systems. Trace levels of contaminants\nare present in all major rivers in southern Alberta, Canada, with concentrations higher downstream\nof anthropogenic inputs like agricultural land-use and inputs of municipal wastewater effluents.\nLongnose dace (Rhinichthys cataractae) were used as a sentinel species to study field-based\npopulation-level responses to contaminants. We hypothesized that biomarker activity, triggered by\ncontaminant exposure, should increase downstream of anthropogenic inputs in two southern Alberta\nrivers, with corresponding relations between biomarker activity and sex ratios, after accounting\nfor age structure. Liver detoxification (ethoxyresorufin-O-deethylase activity = EROD) measured\nat reference and exposed sites on each river differed significantly in only the Bow River system. Sex\nratios varied more downstream of anthropogenic inputs than upstream, but the direction of sex ratio\nbias was inconsistent and temporally dynamic. Sex ratios correlated with liver detoxification in\nonly the Bow River. Taken together, these results suggest that contaminants alter sex ratios in longnose\ndace, but that there is variation in anthropogenic stressors among rivers.
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