Linking mercury exposure to habitat and feeding behaviour in Beaufort Sea beluga whales L.L. Loseto a, ⁎ , G.A. Stern b,c , D. Deibel d , T.L. Connelly d , A. Prokopowicz e , D.R.S. Lean f , L. Fortier e , S.H. Ferguson a,b a Department of Zoology, University of Manitoba, 500 University Cres., Winnipeg MB, Canada R3T 2N2 b Freshwater Institute/Fisheries and Oceans Canada, 501 University Cres., Winnipeg MB, Canada R3T 2N6 c Department of Environment & Geography, University of Manitoba, 500 University Cres., Winnipeg MB, Canada R3T 2N2 d Ocean Sciences Centre, Memorial University, St John's NL, Canada A1C 5S7 e Dept. de Biologie, Université Laval, Pavillon Vachon, Quebec QC, Canada G1K 7P4 f Department of Biology, University of Ottawa, 30 Marie Curie Ottawa ON, Canada K1N 6N5 Received 16 April 2007; received in revised form 24 September 2007; accepted 12 October 2007 Available online 24 October 2007 Abstract Mercury (Hg) levels in the Beaufort Sea beluga population have been increasing since the 1990's. Ultimately, it is the Hg content of prey that determines beluga Hg levels. However, the Beaufort Sea beluga diet is not understood, and little is known about the diet Hg sources in their summer habitat. During the summer, they segregate into social groups based on habitat use leading to the hypothesis that they may feed in different food webs explaining Hg dietary sources. Methyl mercury (MeHg) and total mercury (THg) levels were measured in the estuarine-shelf, Amundsen Gulf and epibenthic food webs in the western Canadian Arctic collected during the Canadian Arctic Shelf Exchange Study (CASES) to assess their dietary Hg contribution. To our knowledge, this is the first study to report MeHg levels in estuarine fish and epibenthic invertebrates from the Arctic Ocean. Although the Mackenzie River is a large source of Hg, the estuarine-shelf prey items had the lowest MeHg levels, ranging from 0.1 to 0.27 μg/g dry weight (dw) in arctic cisco (Coregonus autumnalis) and saffron cod (Eleginus gracilis) respectively. Highest MeHg levels occurred in fourhorn sculpin (Myoxocephalus quadricornis) (0.5 μg/g dw) from the epibenthic food web. Beluga hypothesized to feed in the epibenthic and Amundsen Gulf food webs had the highest Hg levels matching with high Hg levels in associated food webs, and estuarine-shelf belugas had the lowest Hg levels (2.6 μg/g dw), corresponding with the low food web Hg levels, supporting the variation in dietary Hg uptake. The trophic level transfer of Hg was similar among the food webs, highlighting the importance of Hg sources at the bottom of the food web as well as food web length. We propose that future biomagnification studies incorporate predator behaviour with food web structure to assist in the evaluation of dietary Hg sources. © 2007 Elsevier B.V. All rights reserved. Keywords: Amundsen Gulf; Delphinapterus leucas; Diet; Biomagnification 1. Introduction Mercury (Hg) in the form of methyl mercury (MeHg) bioaccumulates in organisms over time, and biomagnifies at each trophic level (Morel et al., 1998). As a result, Hg Available online at www.sciencedirect.com Journal of Marine Systems 74 (2008) 1012 – 1024 www.elsevier.com/locate/jmarsys Abbreviations: Hg, Mercury; THg, total mercury; MeHg, methyl mercury; BMF, biomagnification factor. ⁎ Corresponding author. Tel.: +1 204 984 2425; fax: +1 204 984 2403. E-mail address: losetol@dfo-mpo.gc.ca (L.L. Loseto). 0924-7963/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmarsys.2007.10.004