Understanding and Managing Mercury Bioaccumulation in Sport Fish

Led By

Lake and Reservoir Researchers

Study Area

Statewide

Project Status

Completed

Research Objectives

• To better understand the bioaccumulation of mercury in sport fish, inform development of consumption advisories, and minimize health risks to anglers.​

Project Description

According to the Environmental Protection Agency and Food and Drug Administration, fish represent an excellent source of low-calorie protein. However, eating fish with high mercury concentrations can be a potential health risk.

To protect the health of Colorado's anglers and maintain the quality of angling opportunities, the Lake and Reservoir Research group investigates methods to reduce mercury concentrations in fish, and act as sport fish and food web advisor’s to the Colorado Department of Public Health and Environment’s Technical Advisory Committee on mercury advisories.

A recent study on Narraguinnep Reservoir (southwest Colorado) conducted by CPW and researchers from Colorado State University found that ‘triploid’ walleye (have a third set of chromosomes and cannot reproduce naturally) stocked by CPW had 22-24% lower mercury concentrations on average than their normal, naturally-reproducing ‘diploid’ counterparts. This study revealed that stocking triploid fish alone or in tandem with other mitigation strategies can lead to safer fish for anglers to eat.

The inability of triploid walleye to reproduce affects their mercury levels. Spawning is energetically costly, particularly for female fish that need to develop eggs. As a result, normal, diploid walleye need to eat more food to grow and successfully spawn every year when compared to triploid walleye. Since most (>95%) of the mercury present in predatory fish comes from their prey, eating less food to grow the same amount means triploid fish are exposed to less mercury, and have lower mercury concentrations.

Another recent study was conducted in Colorado to determine the best predictors of mercury concentrations in small walleye and smallmouth bass (15 inches) and large (34 inches) northern pike. We used a machine learning approach to test the different predictors and found that the best predictors of walleye and smallmouth bass mercury concentrations where system-specific measurements of productivity and forage base quality (the higher the productivity and quality of the forage base, the lower the mercury concentrations). The best predictors of large northern pike mercury concentrations were related to the stocking of catchable rainbow trout. Data indicated that large northern pike often eat stocked rainbow trout, and as a result, northern pike mercury concentrations can be lower where heavy rainbow trout stocking occurs (diluted by high calorie prey containing relatively little mercury). This approach could be applied to identify potential areas/systems of concern, and predict whether sport fish Hg concentrations may change as a result of a variety of factors to help prioritize, focus, and streamline monitoring efforts to effectively and efficiently inform human and ecological health.

Associated Publications

Farrell, C.J., B.M. Johnson, A.G. Hansen, and C.M. Myrick. 2022. Induced triploidy reduces mercury bioaccumulation in a piscivorous fish. Canadian Journal of Fisheries and Aquatic Sciences 79:202-212 (Received Editor’s Choice Award).

Eagles-Smith, C.A., J.G. Wiener, C. Eckley, J.J. Willacker, D.C. Evers, M. Marvin-DiPasquale, D. Obrist, J. Fleck, G. Aiken, J.M. Lepak, A.K. Jackson, J. Webster, A.R. Stewart, J. Davis, C. Alpers, and J.T. Ackerman. 2016. Mercury in western North America: a synthesis of environmental contamination, fluxes, bioaccumulation and risk to fish and wildlife. Science of the Total Environment 568:1213-1226.

Eagles-Smith, C.A., J.T. Ackerman, J.J. Willacker, M.T. Tate, M.A. Lutz, J. Fleck, A.R. Stewart, J.G. Wiener, D.C. Evers, J.M. Lepak, J. Davis, and C. Flanagan Pritz. 2016. Spatial and temporal patterns of mercury concentrations in freshwater fishes across the Western US and Canada. Science of the Total Environment 568:1171-1184.

Jackson, A., D.C. Evers, C.A. Eagles-Smith, J.T. Ackerman, J.J. Willacker, J.T. Elliott, J.M. Lepak, S.S. VanderPol, and C.E. Bryan. 2016. Mercury risk to avian piscivores across the western United States and Canada. Science of the Total Environment 568:685-696.

Johnson, B.M., J.M. Lepak, and B.A. Wolff. 2015. Effects of prey assemblage on mercury bioaccumulation in a piscivorous sport fish. Science of the Total Environment 506-507:330-337.

Lepak, J.M., M.B. Hooten, C.A. Eagles-Smith, M.T. Tate, M.A. Lutz, J.T. Ackerman, J.J.Jr.  Willacker, D.C. Evers, J.G. Wiener, C. Flanagan Pritz, and J. Davis. 2016. Assessing potential health risks to fish and humans using mercury concentrations in inland fish from across western Canada and the United States. Science of the Total Environment 571:342-354.

Lepak, J.M., M.B. Hooten, and B.M. Johnson. 2012. The influence of external subsidies on diet, growth and Hg concentrations of freshwater sport fish: implications for fisheries management and the development of fish consumption advisories. Ecotoxicology 21(7):1878-1888.

Lepak, J.M., K.D. Kinzli, E.R. Fetherman, W.M. Pate, A.G. Hansen, E.I. Gardunio, C.N. Cathcart, W.L. Stacy, Z.E. Underwood, M.M. Brandt, C.M. Myrick, and B.M. Johnson. 2012. Manipulation of growth to reduce sport fish mercury concentrations on a whole-lake scale. Canadian Journal of Fisheries and Aquatic Sciences 69(1):122-135.

Lepak, J.M., B.A. Wolff, B.M. Johnson M.B. Hooten, and A.G. Hansen. 2023. Predicting sport fish mercury contamination in heavily managed reservoirs: implications for human and ecological health. PLOS ONE 18:e0285890.

Stacy, W.L., and J.M. Lepak. 2012. Relative influence of prey mercury concentration, prey energy density and predator sex on sport fish mercury concentrations. Science of the Total Environment 437:104-109.

Taylor, M.S., C.T. Driscoll, J.M. Lepak, D.C. Josephson, K.J. Jirka, and C.E. Kraft. 2020. Temporal trends in fish mercury concentrations in an Adirondack Lake managed with a continual predator removal program. Ecotoxicology 29:1762-1773.

Willacker, J.J., C.A. Eagles-Smith, M.A. Lutz, M.T. Tate, J.T. Ackerman, and J.M. Lepak. 2016. The influence of reservoirs and their water management on fish mercury concentrations in Western North America. Science of the Total Environment 568:739-748.

Wolff, B.A., B.M. Johnson, and J.M. Lepak. 2017. Changes in sport fish mercury concentrations from food web shifts suggest partial decoupling from mercury loading in two Colorado reservoirs. Archives of Environmental Contamination and Toxicology 72:167-177.