Indigenous peoples of Canada have relied on traditional or country foods (i.e. foods harvested from the land and water) for millennia. These foods are often highly nutritious, and are of significant cultural and economic value. In the Canadian north, subsistence food fishes are very important to Indigenous communities, both in terms of food security and culture. Balancing the health risks and benefits of eating subsistence fishes is a complex problem.
Some northerners have become wary of eating their traditional country foods due to both perceived and real risks of contaminants. The presence of mercury in the atmosphere, water and traditional foods has received a lot of attention over the past several decades, and many lakes in the Canadian north have specific mercury advisories when levels in fish are high enough that health authorities recommend limiting consumption.
When people are afraid of eating their traditional foods, they switch to a market-based diet which poses a different set of health risks. Studies have shown this is linked with increased risks of diabetes, cardiovascular disease and other illnesses because the market-based foods that are available in remote northern regions of Canada are often highly processed and lack the building blocks of proper nutrition. While we have made quite a bit of progress in identifying the risks of eating fish contaminated with mercury, it is also important to identify which can be consumed safely. Assessing both risks and benefits is key to helping northerners make the safest, healthiest food choices, and for determining the best courses of action for improving food security.
Methodology
Between 2013 and 2015, seven wild-caught freshwater fish species were harvested from eight lakes in the Dehcho Region of the Northwest Territories. The sampling, in addition to other aspects of the study, was participatory, community- driven science. Very early on in the project, we realized that it was important to not only quantify the risks of eating fish, but also the benefits. To link people’s fish consumption patterns to contaminant concentrations in their bodies we worked alongside a research team from the University of Waterloo’s School of Public Health and Health Systems led by Dr. Brian Laird.
Our First Nations partners were involved in all aspects of the field research. We fished, hunted, cooked and lived together. They taught us about what their traditional foods and land meant to them; we taught them some transferable skills in environmental sampling and community-based monitoring. We consulted them on how samples should be taken, how they should be treated and disposed of and how the community wanted the information communicated to them.
Once we worked out which fish and lakes had the safest mercury levels, which fish had the best nutrient-to-mercury ratios, and which fish people were eating, we consulted a biogeochemist. Dr. Brian Branfireun, professor in the Department of Biology at Western University. Dr. Branfireun tracks mercury from the catchments to the lakes, and identifies how it transforms from inorganic mercury (the silver we see in thermometers) into methyl mercury (the type that bioaccumulates) in sediment and water. Dr. Branfireun’s data was fed into my fish ecology models, as well as models of food chain structure, life history and spatial variation in mercury levels in fish among lakes. Together with dietary questionnaire data gathered by our social science colleague Dr. Kelly Skinner (also from the School of Public Health and Health Systems at the University of Waterloo), these data were ultimately fed into Dr. Laird’s models of human exposure. Alongside this information, Dr. Skinner collected data about what community members had heard about contaminants as well as how that information affected the decisions they made about the country foods they harvested and ate.
Outcomes
Not surprisingly, fish that feed higher in the food chain had higher mercury levels than fish that feed lower in the food chain. We found that Lake Whitefish, Cisco and Sucker had the lowest levels of mercury and the highest levels of healthy fatty acids (Figure 1).
FIGURE 1: Fatty acid: mercury ratios, based on median values, for fish species harvested in freshwater lakes of the Mackenzie Valley Region, Northwest Territories, Canada (2013, 2014, and 2015), as compared with the minimum ratio established using guidelines. Both DHA and EPA are healthy fatty acids. From left to right for each species, DHA:Hg ratios are represented in black, while EPA + DHA:Hg ratios are represented in light grey, and N-3:Hg represented in dark grey. The solid reference line indicates the minimum ratio for DHA, while the long-dashed line indicates the minimum ratio for EPA + DHA, and the short-dashed line indicates the minimum ratio for total omega-3 unsaturated fatty acids.
We continue working to understand why healthy fatty acid levels and nutrient-to-mercury ratios differ so much among lakes. Ultimately, this should help to determine how human-induced changes to water quality and lake catchments may affect levels of nutrients and mercury in food fishes.
Conclusions
There are safe fish to eat in every lake sampled. Fish with the highest fatty acid levels and lowest mercury levels tended to be Cisco, Lake Whitefish, and Lake Trout.
Complex, species-specific interactions exist between mercury and omega-3 fatty acids. We are now pursuing subsequent research which examines the drivers of these relationships – basically, what kind of lakes produce fish (or at least a few types of fish) with high fatty acid levels and low mercury.
Doing this type of research takes trust among researchers, communities and community liaisons. That takes time – and sometimes a lot of time, but the biggest rewards are the relationships developed, which allow greater insight and impact for results.
Laird, M.J., Henao, J.J.A., Reyes, E.S., Stark, K.D., Lo, G. Swanson, H.K. & Laird, B.D. (2018). Mercury and omega-3 fatty acid profiles in freshwater fish of the Dehcho Region, Northwest Territories: Informing risk benefit assessments. Science of the Total Environment, 637-638, 1508-1517.
Contacts: Heidi Swanson, Department of Biology; Brian Laird, School of Public Health and Health Systems
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