Contaminant Bioaccumulation and Trophic Characterization of Top-Level Predatory Fishes

Both regulatory and ecological considerations warrant evaluation of contaminant bioaccumulation in top-level predatory fishes. However, variation within and among syntopic top predators is often not well understood. We are comparing in detail trophic position and trace element bioaccumulation in four species of predatory fish from Beaver Dam Creek, SC, USA. This Savannah River tributary located on the Savannah River Site, has a long history of exposure to coal combustion wastes from a coal fired power plant in its headwaters. Two herbivorous invertebrates, freshwater clams and heptageniid mayflies, are included to compare elements entering the food web with those accumulating in the top predators. Fish samples were stratified across the broadest size ranges available for channel catfish (N=51), longnose gar (N=19), largemouth bass (N=34), and bowfin (N=5). Stable isotope (N and C) analyses were employed to assess the trophic organization. Differences in trophic position was noted both between and within species. Trophic position of largemouth bass and longnose gar broadly overlap as the highest level predators. These two species were higher than all but the largest channel catfish. Small sample size precluded rigorous analysis of the bowfin, but they appeared intermediate, overlapping more with the largemouth bass and longnose gars. Concurrent trace element analysis is assessing bioaccumulation of 16 analytes including metals and metalloids commonly associated with coal combustion wastes. Comparison of element accumulation in muscle, liver, and gonad samples is providing a more comprehensive assessment of exposure and risk. Analysis of muscle is critical because contaminant concentrations are integrated over the longest time. It also constitutes a large portion of body mass and is the portion consumed by humans. Some contaminants accumulate more in the liver and generally contaminant burden of the liver reflects more recent exposure. Accumulation in the ovaries is critical for assessing risk of reproductive failure due to exposure to selenium, a common constituent of coal combustion wastes. Within a species, the influences of size, sex, sexual maturity, and trophic level are being compared. Concentrations of many elements accumulated to higher levels in the invertebrate herbivores than in the upper level predators. These elements were entering the aquatic food web, but not being transferred to muscle tissue of the higher predators. Others elements were accumulating at higher levels in the predators. Bioaccumulation of many elements differed among and within the predators. Concentrations of most elements were higher in the livers of the predators than muscle tissue.