Determining optimal sampling strategies for monitoring mercury and reproductive success in common loons in the Adirondacks of New York


The common loon (Gavia immer), a top predator in the freshwater food web, has been recognized as an important bioindicator of aquatic mercury (Hg) pollution. Because capturing loons can be difficult, statistical approaches are needed to evaluate the efficiency of Hg monitoring. Using data from 1998 to 2016 collected in New York’s Adirondack Park, we calculated the power to detect temporal changes in loon Hg concentrations and fledging success as a function of sampling intensity. There is a tradeoff between the number of lakes per year and the number of years needed to detect a particular rate of change. For example, a 5% year−1 change in Hg concentration could be detected with a sampling effort of either 15 lakes per year for 10 years, or 5 lakes per year for 15 years, given two loons sampled per lake per year. A 2% year−1 change in fledging success could be detected with a sampling effort of either 40 lakes per year for 15 years, or 30 lakes per year for 20 years. We found that more acidic lakes required greater sampling intensity than less acidic lakes for monitoring Hg concentrations but not for fledging success. Power analysis provides a means to optimize the sampling designs for monitoring loon Hg concentrations and reproductive success. This approach is applicable to other monitoring schemes where cost is an issue.

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We greatly appreciate the many hours the Adirondack field crew has devoted each summer to document the return rate and reproductive success of the color-banded study loons. The Adirondack Watershed Institute of Paul Smith’s College and the Adirondack Ecological Center of SUNY ESF generously provided students annually to assist with monitoring the banded loons on some of our study lakes. The staff of the New York State Department of Environmental Conservation, the Wildlife Conservation Society’s Zoological Health Program, and Calvin College have provided in-kind staff support and equipment for the loon capture and sampling fieldwork each year.


Financial support was provided by the New York State Energy Research and Development Authority, the Wildlife Conservation Society, The Wild Center, the Raquette River Advisory Council, and numerous private foundations and donors.

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Correspondence to Yang Yang.

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Yang, Y., Yanai, R.D., Schoch, N. et al. Determining optimal sampling strategies for monitoring mercury and reproductive success in common loons in the Adirondacks of New York. Ecotoxicology 29, 1786–1793 (2020).

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  • Power analysis
  • Sampling guidance
  • Mercury
  • Fledging success
  • Bioindicator
  • Common loon
  • Lake acidity
  • Adirondack Park