Current concentrations and spatial and temporal trends in mercury in Great Lakes Herring Gull eggs, 1974–2009
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.
KeywordsMonitoring Great Lakes Herring Gull Mercury
Many people have assisted with the collection of Herring Gull eggs over the years and their efforts are greatly appreciated: Michael Gilbertson, Glen Fox, Andy Gilman, Doug Hallett, Jim Learning, John Elliott, Stan Teeple, Pierre Mineau, John Ryder, Gary Shugart, John Struger, Christine Bishop, Karen Pettit, Rob Dobos, Glenn Barret, Cynthia Pekarik, Tania Havelka, Tammy Dobbie, Steve Elliott, Brian McCattie, Ralph Morris and his students, Jim Quinn and his students, Ray Faber and his students, Keith Grasman and his students, Lee Harper, Connie Adams, Susan Elbin, Liz Craig, Dave Best, Brian Ratcliff, Laird Shutt, Kim Williams, Doug Crump, Don Ryckman, Margie Koster, Larry Benner, Earl Walker, Peter Ross, Tyler Hoar, Dave Andrews, Kate (Jermyn) Gee and Pete Ewins. Routine chemical analyses were directed by Bryan Wakeford. Fish Contaminants Monitoring Program: Fish collections: Michael Keir, Mandi Clark and the Captain and crew of the C.C.G.S. Shark and Kelso. Sample processing and preparation: Mary Malecki and Karla Passow. Liane O’Keefe conducted the literature search.
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