A Bayesian framework for assessing contamination trends in fish communities in the Great Lakes

Session: 07. - Effects of Environmental Contamination on Fish Communities

Ariola Visha, University of Toronto Scarborough, [email protected]
Nilima Gandhi, Ministry of the Environment and Climate Change, [email protected]
Satyendra Bhavsar, Ontario Ministry of Environment and Climate Change, [email protected]
George Arhonditsis, University of Toronto Scarborough, [email protected]

Abstract

Legacy contaminants have posed constraints on fish consumption around the Great Lakes. This study examines the spatio-temporal trends of mercury (THg), and PCBs in eleven fish species across the Canadian waters. Dynamic linear models were developed to detect long-term trends and non-monotonic patterns in fish contaminant records. We used Bayesian hierarchical modelling to evaluate the variability between inshore and offshore locations, as well as to examine the hypothesis that invasive species have induced distinct shifts on fish contamination trends. Current results indicate that THg concentrations have been gradually declining, but the rate of decline in recent years has slowed down. THg decrease was more pronounced in top fish predators whereas benthivorous fish species mainly underwent wax-and-wane cycles with a weaker evidence of a long-term decreasing trend. Historically contaminated regions, designated as Areas of Concern, and bays receiving riverine inputs are still characterized by high concentrations across all species examined. Similarly, our analysis provided evidence of a deceleration of the PCB declining rates accompanied by a gradual establishment of species-specific equilibrium concentrations, around which there is considerable year-to-year variability. Our study suggests that the reduced emissions have brought about distinct positive changes in fish concentrations, but past historical contamination along with other stressors (invasive species, climate change) continue to impact current levels.

1. Keyword
mercury

2. Keyword
PCBs

3. Keyword
fish management