Project background
Mercury in fish is a public health concern, particularly for communities that rely on local fish for food and cultural practices. This project will investigate how aquatic invasive species may change lake ecosystems in ways that affect how mercury moves through sediments, water, and food webs and ultimately accumulates in fish.
MAISRC researchers will collect and analyze samples from sediments, water, aquatic plants, invertebrates, and fish across multiple lakes with varying levels of invasion. The team will also study how invasive species may influence fish growth and how growth rates affect mercury concentrations. Using these findings, the project will model different fish harvest and consumption scenarios to explore ways to reduce human exposure to mercury.
The work is being conducted in close collaboration with the Leech Lake Band of Ojibwe Division of Resource Management and partners at the Minnesota Department of Natural Resources and U.S. Geological Survey. Results will help inform fish consumption guidance and management strategies that protect public health while supporting tribal traditions and fisheries.
Project Activities
- Measure mercury across lake food webs: Sample sediments, water, aquatic plants, invertebrates, and fish in lakes with different levels of invasion by zebra mussel and starry stonewort to determine how these species influence mercury and methylmercury concentrations from the bottom of the food web to fish.
- Evaluate impacts on fish growth and mercury accumulation: Analyze historical and newly collected fish data to understand how invasive species may change fish growth rates and how those changes influence mercury levels in fish.
- Assess fish harvest strategies to reduce mercury exposure: Work with partners to model different fish harvest and consumption scenarios and identify strategies that could lower human exposure to mercury while sustaining fisheries.
- Share results and engage partners: Collaborate with the Leech Lake Band of Ojibwe, Minnesota Department of Natural Resources, and U.S. Geological Survey and communicate findings through outreach, scientific publications, conferences, and public engagement.
Phases
Phase I
Title: Zebra mussel impacts on fish mercury concentrations
Project manager: Gretchen Hansen, Department of Fisheries, Wildlife, and Conservation Biology
Lab: Hansen Lab
Collaborating partners:
Caren Ackley, Mark Leuhring, and Adam Ray, Great Lakes Indian Fish and Wildlife Commission
Jennifer Brentrup, MN Pollution Control Agency
Paul Radomski, Heidi Rantala, and Isaiah Tolo, MN Department of Natural Resources
Dr. Erin Schliep, North Carolina State University
Tyler Wagner, Pennsylvania State University
Project timeline: 2024-2025
Funded by: MAISRC and the Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources
This project examined how zebra mussel invasion affects mercury concentrations in fish and developed tools to better predict fish mercury risk in lakes that are not regularly sampled. Using a modified before–after–control–impact design across 357 Minnesota lakes, researchers compared fish mercury levels before and after invasion while accounting for trends in uninvaded reference lakes. Mercury concentrations increased in four of six species following invasion, with average increases ranging from 6% in walleye to 21% in black crappie. After invasion, walleye and northern pike were more likely to exceed the 0.22 parts-per-million threshold used to guide fish consumption advice, indicating that zebra mussel establishment can reduce the number of safe meals per month for some commonly harvested species.
In parallel, the team developed and validated a predictive modeling framework to estimate fish mercury risk statewide. By linking fish mercury data from Minnesota, Wisconsin, and tribal partners with lake characteristics and surrounding land cover, the model generated lake- and species-specific risk estimates. The model accurately classified whether average mercury concentrations in a lake-species combination were above or below the 0.22 ppm advisory threshold 90% of the time. These outputs were translated into probability-based risk categories and length-based thresholds to help managers prioritize monitoring, refine sampling strategies, and identify potential mercury “hot spots” across Minnesota and Wisconsin.
The results demonstrate that zebra mussel invasion is associated with measurable increases in fish mercury at a regional scale and provide a practical, science-based tool to support fish consumption guidance and strategic monitoring decisions.
Media
- Study reveals elevated mercury levels in fish associated with zebra mussel invasions
- Study: Walleye in lakes with zebra mussels have higher mercury levels | MPR News
- Invasive zebra mussels are associated with elevated mercury levels in fish, study finds
- MN invasive zebra mussels linked to higher mercury levels in fish | FOX 9 Minneapolis-St. Paul
- Researchers discover a new health concern in Minnesota lakes infested by zebra mussels
- University of Minnesota study shows zebra mussels tied to elevated fish mercury
- Study shows zebra mussels contribute to elevated mercury levels in walleye and aquatic food webs
- Mercury research raises more questions about South Dakota's lax approach to zebra mussels - Brookings Register
- Zebra mussels and mercury in fish: Why a new study’s findings are alarming | KAXE
- Zebra mussels and mercury in fish: An alarming Minnesota study
- Is Your Shorelunch Full of Mercury??
- Another Texas lake infested with invasive Zebra Mussels
- Mercury pollution a problem in northern Minnesota lakes