Marine mammals and human health in the Eastern Bering Sea : using an ecosystem-based food web model to track PCBs

The comprehensive changes that have occurred in the Bering Sea over the last 30 years have prompted a wide range of studies to better understand the ecosystem as a whole. One set of studies has used the Ecopath with Ecosim (EwE) modelling software to synthesise existing biological data and gain insight into how the ecosystem was before and after the system-wide changes. This modelling framework provides a means for tracing contaminants through the ecosystem, and evaluating the role that persistent organic pollutants (POPs) may have played in the changing dynamics of the eastern Bering Sea. Using the EwE software, the likely pathways of PCB flow within the eastern Bering Sea were identified and health implications of contaminant exposure for Steller sea lions, other species of marine mammals, and humans were evaluated. The base EwE model was refined from existing models and validated with traditional stock assessment data. Ecotracer (a component of the EwE software) tracked the bioaccumulation of contaminants moving through the system with biomass. The models estimated contaminant concentrations for species and functional groups that have not previously been measured. Results suggest that PCB concentrations for most species in the eastern Bering Sea have remained below threshold levels associated with negative reproduction and survival effects. However, these concentrations may have subtle effects on adults and more serious effects on foetuses and nursing young, which could inhibit the recovery of Steller sea lions and other species that have declined in the eastern Bering Sea. Although the benefits of traditional foods appear to continue to outweigh the risks posed by contaminants for humans, PCB exposure and dietary intake for many Alaska Natives subsisting on marine mammals is above the USEPA Daily Reference Dose. Results extend the existing eastern Bering Sea models and are important in terms of management alternatives for marine mammals and human health. They also synthesise evidence regarding the presence, extent, and movement of PCBs throughout the system. The refined eastern Bering Sea models are useful tools for exploring different scenarios and hypotheses, to inform resource managers, and to further our understanding of this ecosystem.Science, Faculty ofResources, Environment and Sustainability (IRES), Institute forGraduat