Mercury Temporal Trends in Top Predator Fish of the Laurentian Great Lakes from 2004 to 2015: Are Concentrations Still Decreasing?

Abstract

Mercury (Hg) concentration trends in top predator fish (lake trout and walleye) of the Great Lakes (GL) from 2004 to 2015 were determined by Kendall-Theil robust regression with a cluster-based age normalization method to control for the effect of changes in lake trophic status. When data from the GLs (except Lake Erie) are combined, a significant decreasing trend in the lake trout Hg concentrations was found between 2004 and 2015 with an annual decrease of 4.1% per year, consistent with the decline in regional atmospheric Hg emissions and water Hg concentrations. However, a breakpoint was detected with a significant decreasing slope (-8.1% per year) before the breakpoint (2010), and no trend after the breakpoint. When the lakes are examined individually, Lakes Superior and Huron, which are dominated by atmospheric Hg inputs and are more likely than the lower lakes to respond to declining emissions from areas surrounding the GL, have significant decreasing trends with rates between 5.2 and 7.8% per year from 2004 to 2015. These declining trends appear to be driven by decreasing regional atmospheric Hg emissions although they may be partly counterbalanced by other factors, including increasing local emissions, food web changes, eutrophication, and responses to global climate change. Lakes Michigan, Erie and Ontario may have been more impacted by these other factors and their trends changed from decreasing to non-decreasing or increasing in recent years.

How closely do mercury trends in fish and other aquatic wildlife track those in the atmosphere? – Implications for evaluating the effectiveness of the Minamata Convention

“…After about 2005, however, trend reversals were detected in most species at some locations. Zhou et al (2017) also detected a breakpoint at~2010 in fish Hg trends in the Great Lakes, with a significant decreasing trend before 2010 and no trend or an increasing trend since then.…”

Understanding factors influencing the detection of mercury policies in modelled Laurentian Great Lakes wet deposition

“…However, negative trends in other Great Lakes media (air, water, fish) have been more consistently reported for this approximate period. 32,[80][81][82] For instance, Zhou et al find significant declines in predatory fish concentrations when data for all lakes but Erie are combined (though some lakes show increases or stable concentrations in the 2010s, following steep declines between 2005 and 2010). 80 Similar patterns of decreases and then stabilization or increase have been reported for GEM concentrations (though certain sites, particularly in the Northeast, show steady and statistically significant declines), 32,81 and other analyses of fish concentrations.…”

“…32,[80][81][82] For instance, Zhou et al find significant declines in predatory fish concentrations when data for all lakes but Erie are combined (though some lakes show increases or stable concentrations in the 2010s, following steep declines between 2005 and 2010). 80 Similar patterns of decreases and then stabilization or increase have been reported for GEM concentrations (though certain sites, particularly in the Northeast, show steady and statistically significant declines), 32,81 and other analyses of fish concentrations. 83 Although our analysis is not designed to explain these historical trends explicitly, it does aim to use modelling experiments to generate insight into the relative influence of factors that mediate the connection between anthropogenic emissions changes and wet deposition in this region.…”

Polychlorinated biphenyls and organochlorine pesticides concentration patterns and trends in top predator fish of Laurentian Great Lakes from 1999 to 2014

“…The sampling information and analysis methods were described in detail in our previous papers (sample handling and preparation details given in the Electronic Supplementary Information (ESM) Table S1) (Chang et al, 2012;Zananski et al, 2011;Zhou et al, 2017). In brief, 50 fish samples (600-700 mm length lake trout from LH, LM, LO and LS, and 400-500 mm length walleye from LE) were collected and composited into ten composite samples of five fish in each lake annually for contaminant analysis.…”

“…The United States and Canada have been collecting and measuring concentrations of legacy contaminants in the Great Lakes (GL) fish, for example lake trout (Salvelinus namaycush) and walleye (Sander vitreus) since the late 1970s as part of what is now called the Great Lakes Fish Monitoring and Surveillance Program (GLFMSP) in the U.S. (Chang et al, 2012;Zananski et al, 2011;Zhou et al, 2017) and in Canada the Sports Fish Contaminant Monitoring Program (SFCMP) (Bhavsar et al, 2007) and the Fish Contaminants Monitoring and Surveillance Program (FCMSP) (McGoldrick and Murphy, 2016). Additionally, PCBs were designated as a Chemical of Mutual Concern (CMC) by the Governments of Canada and the United States in February of 2014, under the Great Lakes Water Quality Agreement (GLWQA).…”