Role of stream fish movement in selenium ecotoxicology

Stream fishes may move to access remote resources, escape locally unsuitable conditions, or recolonize extirpated populations.  Exposure to environmental contaminants therefore may exhibit considerable spatial and temporal heterogeneity, necessitating an understanding of fish movement in ecotoxicology.  First, we review evidence for fish movement within and among connected streams, and relate movement dynamics to contaminant exposure.  Second, we describe the importance of movement for selenium bioaccumulation through dietary exposure pathways.  Third, we present a case study using data from the West Virginia Department of Environmental Protection to evaluate selenium bioaccumulation in two stream sites (Ash Fork and Sycamore Creek).  Repeated samples revealed consistently low aqueous concentrations of selenium in each site (< 1 ppb) but fish tissue concentrations exhibited substantial variability, with some individuals reaching whole-body selenium concentrations > 10 ppm.  Both sites were located near selenium-contaminated confluences, suggesting the possible influence of fish movement.  Moreover, fish tissue concentrations in Sycamore Creek were substantially higher in spring samples than in summer or fall, suggesting the possibility that spawning-run individuals were exposed to selenium-enriched diets downstream.  We discuss the implications of fish movement for calculating bioaccumulation factors, and recommend additional research to evaluate exposure using otolith microchemistry.