, Volume 80, Issue 1-4, pp 871-880

Common loons (Gavia immer) nesting on low ph lakes in northern Wisconsin have elevated blood mercury content

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Abstract

The Wisconsin Department of Natural Resources conducted a pilot study during the summer of 1991 to determine the extent of mercury (Hg) exposure in common loons (Gavia immer) breeding in Wisconsin. Loons are at risk to elevated Hg exposure in Wisconsin because they often nest on acidified, low alkalinity lakes. Fish from these lakes bioaccumulate MeHg to a greater extent than biota from neutral pH lakes. Using nightlighting techniques, 35 adult loons were captured on 20 northern Wisconsin lakes (pH=5.0–8.7) in 1991. Blood and feather samples were collected for Hg analysis. The mean Hg content of blood cells collected from adult loons on low pH lakes (pH≤6.3) was significantly greater than the Hg content of adult loons collected on neutral/alkaline pH lakes (pH>-7.0) (F=19.87, P<0.001). There was a highly significant negative linear relationship between adult loon blood cell Hg concentrations and lake pH (r2=0.38, F=15.27, P>0.001); indicating loons nesting on low pH lakes receive greater Hg exposure than loons nesting on neutral pH lakes. The relationship was greater amongst adult males (r2=0.56) than amongst adult females (r2=0.36). Because of this documented exposure, an additional 330 loons were captured 1992-94 on 73 lakes in northern Wisconsin. The Hg exposure of adult and juvenile common loons is being quantified. Individual loons were fitted with unique color-coded leg bands, and the 1992–96 reproductive performance, apnual return rates, and nesting behavior of adult loons with the known Hg exposure is currently being assessed.