Current concentrations and spatial and temporal trends in mercury in Great Lakes Herring Gull eggs, 1974–2009

Abstract

Current concentrations and spatial and temporal trends of total mercury (Hg) were assessed in eggs of the Herring Gull (Larus argentatus) over the period 1974-2009 at 15 sites in the Great Lakes: 2-3 sites per lake and one site in each of 3 connecting channels. Current (2009) concentrations ranged from 0.064 μg/g (wet weight) at Chantry Island (Lake Huron) to 0.246 μg/g at Middle Island (Lake Erie). There were significant inter-colony differences in mean Hg concentrations (2005-2009). Mercury concentrations at 14 of 15 sites declined from 23 to 86% between when it was first measured (usually 1974) and 2009. Declining temporal trends over the entire period (1974-2009) were significant at 10 of the 15 sites. On the other hand, there were no significant trends in mercury over the last 15 years. In the early years, declines of Hg in Herring Gull eggs tracked those in Rainbow Smelt (Osmerus mordax) in most Great Lakes. More recently, declines in gull eggs were more evident than in smelt and may be partially explained by temporal changes in the gull diet. When gull Hg data were adjusted for temporal changes in the gull diet, as inferred from stable nitrogen isotope values in eggs, significant declines in egg mercury levels were found only at 4 of 15 sites. Overall, Hg concentrations have declined in Great Lakes Herring Gull eggs over the period 1974-2009 but changes in the gull diet may be contributing, in part, to those declines. Examination of contaminant temporal trends in multiple indicator species will ensure accurate inferences regarding contaminant availability in the environment.

Avian mercury exposure and toxicological risk across western North America: A synthesis

“…Bird reproduction is particularly sensitive to mercury toxicity, with numerous documented deleterious effects to bird health, condition, behavior, and productivity (Table 1; Scheuhammer et al, 2007; Wiener et al, 2003). Together, these characteristics make birds useful bioindicators for local mercury contamination and regional monitoring programs (Day et al, 2012; Evers et al, 2011; Monteiro and Furness, 1995; Provencher et al, 2014; Weseloh et al, 2011). …”

Mercury in the Great Lakes region: bioaccumulation, spatiotemporal patterns, ecological risks, and policy

“…As with museum specimens and sediment core data, herring gull eggs from the Great Lakes (Weseloh et al 2011) indicate decreases in biotic mercury between 1974 and 2009. Concentrations of mercury in eggs at 14 of 15 sites declined during the study period (range in declines, 23-86%), and declines were statistically significant at 10 of 15 sites.…”

“…In both species, normalized mercury concentrations were higher in inland lakes versus the Great Lakes. Weseloh et al (2011), who analyzed a 35-year dataset of mercury in eggs of herring gulls (Larus argentatus), observed a 4-fold range in concentrations. Recent concentrations in eggs were lowest at a Lake Huron site and highest concentrations at a site in Lake Erie and the St. Lawrence River.…”

Retrospective analysis of mercury content in feathers of birds collected from the state of Michigan (1895–2007)

“…Comprehensive monitoring of contaminants in Great Lakes biota did not begin until the early 1970s with programs such as the Canadian Wildlife Service's herring gull monitoring program. From this program, a significant downward trend in Hg content of herring gull eggs was observed at 10 of 15 Great Lakes colonies from the early 1970s to 2009 (Koster et al 1996;Weseloh et al 2011). Concentrations of Hg in Great Lakes fish have generally decreased since the early 1970s, though recent data suggest that levels in certain species and particular geographical regions may be increasing (French et al 2006;Bhavsar et al 2010).…”