title: Mercury levels in herring gulls and fish: 42 years of spatio-temporal trends in the Great Lakes.
abstract: Total mercury levels in aquatic birds and fish communities have been monitored across the Canadian Great Lakes by Environment and Climate Change Canada (ECCC) for the past 42 years (1974-2015). These data (22 sites) were used to examine spatio-temporal variability of mercury levels in herring gull (Larus argentatus) eggs, lake trout (Salvelinus namaycush), walleye (Sander vitreus), and rainbow smelt (Osmerus mordax). Trends were quantified with dynamic linear models, which provided time-variant rates of change of mercury concentrations. Lipid content (in both fish and eggs) and length in fish were used as covariates in all models. For the first three decades, mercury levels in gull eggs and fish declined at all stations. In the 2000s, trends for herring gull eggs reversed at two sites in Lake Erie and two sites in Lake Ontario. Similar trend reversals in the 2000s were observed for lake trout in Lake Superior and at a single station in Lake Ontario. Mercury levels in lake trout continued to slowly decline at all of the remaining stations, except for Lake Huron, where the levels remained stable. A post-hoc Bayesian regression analysis suggests strong trophic interactions between herring gulls and rainbow smelt in Lake Superior and Lake Ontario, but also pinpoints the likelihood of a trophic decoupling in Lake Huron and Lake Erie. Continued monitoring of mercury levels in herring gulls and fish is required to consolidate these trophic shifts and further evaluate their broader implications.
authors.affiliation: Environment and Climate Change Canada, 867 Lakeshore Road, Burlington, Ontario L7S 1A1, Canada; Department of Physical and Environmental Sciences, University of Toronto, Toronto, Ontario M1C 1A4, Canada. Electronic address: Agnes.Richards@canada.ca.
authors.forename: E Agnes
authors.initials: EA
authors.lastname: Blukacz-Richards
authors.affiliation: Department of Physical and Environmental Sciences, University of Toronto, Toronto, Ontario M1C 1A4, Canada.
authors.forename: Ariola
authors.initials: A
authors.lastname: Visha
authors.affiliation: Environment and Climate Change Canada, 867 Lakeshore Road, Burlington, Ontario L7S 1A1, Canada.
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Graham
authors.affiliation: Environment and Climate Change Canada, 867 Lakeshore Road, Burlington, Ontario L7S 1A1, Canada.
authors.forename: Daryl L
authors.initials: DL
authors.lastname: McGoldrick
authors.affiliation: Environment and Climate Change Canada, 867 Lakeshore Road, Burlington, Ontario L7S 1A1, Canada.
authors.forename: Shane R
authors.initials: SR
authors.lastname: de Solla
authors.affiliation: Environment and Climate Change Canada, 867 Lakeshore Road, Burlington, Ontario L7S 1A1, Canada.
authors.forename: David J
authors.initials: DJ
authors.lastname: Moore
authors.affiliation: Department of Physical and Environmental Sciences, University of Toronto, Toronto, Ontario M1C 1A4, Canada.
authors.forename: George B
authors.initials: GB
authors.lastname: Arhonditsis
mesh_terms: D000818:Animals; D001499:Bayes Theorem; D002170:Canada; D046091:Charadriiformes; D057231:Climate Change; D004531:Eggs / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods*; D020387:Food Chain; D006114:Great Lakes Region; D060106:Lakes; D016014:Linear Models; D008055:Lipids / Q000737:chemistry; D008628:Mercury / Q000032:analysis*; D010471:Perches; D012044:Regression Analysis; D062211:Spatio-Temporal Analysis; D014337:Trout; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D008055:Lipids; D014874:Water Pollutants, Chemical; D008628:Mercury
keywords: Bayesian inference; Dynamic linear models; Fish; Great Lakes; Herring gulls; Mercury