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Great Lakes Caspian Terns: Egg Contaminants and Biological Implications

John Struger and D. Vaughn Weseloh
Colonial Waterbirds
Vol. 8, No. 2 (1985), pp. 142-149
Published by: Waterbird Society
DOI: 10.2307/1521064
Stable URL: http://www.jstor.org/stable/1521064
Page Count: 8
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Great Lakes Caspian Terns: Egg Contaminants and Biological Implications
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Abstract

Levels of contaminants and eggshell thickness were measured in eggs of Caspian Terns from seven colonies in Lakes Michigan, Huron, and Ontario in 1980/1981. Levels of PCBs, DDE, mirex and hexachlorobenzene (HCB) ranged from 18.5-39.3 ppm (wet wt.), 3.3-8.8 ppm, 0.04-1.57 ppm and 0.03-0.06 ppm, respectively. Eggs from Lake Ontario (Pigeon Is.) had the greatest levels of PCBs, HCB and mirex. DDE levels were greatest in eggs from Lake Míchigan (Gravelly Is.). Eggshell thinning ranged from 0 on Hat. Is. and Ile aux Galets (L. Michigan) to 7.4% on South Limestone Is. (L. Huron). Reproductive success on two Lake Michigan colonies was 1.2-1.3 young/pair. Most residue levels of DDE, PCBs, and mirex in eggs of Caspian Terns from the Great Lakes in 1980 and 1981 have decreased from past levels and do not appear to have had a serious effect on reproduction, eggshell thickness and past and present population size and growth. Comparisons with organochlorine residues in Herring Gulls indicated that generally similar bioaccumulation patterns of contaminants occurred in the two species.

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