title: Global versus local causes and health implications of high mercury concentrations in sharks from the east coast of South Africa.
abstract: Conservation concern regarding the overharvest of global shark populations for meat and fin consumption largely surrounds documented deleterious ecosystem effects, but may be further supported by improved knowledge of possibly high levels in their edible tissues (particularly meat) of the neurotoxin, methylmercury (CH3Hg). For many regions, however, little data exist on shark tissue Hg concentrations, and reasons for Hg variation within and among species or across regions are poorly understood. We quantified total Hg (THg) in 17 shark species (total n=283) from the east coast of South Africa, a top Hg emitter globally. Concentrations varied from means of around 0.1 mg kg(-1) dry weight (dw) THg in hardnose smoothhound (Mustelus mosis) and whale (Rhincodon typus) sharks to means of over 10 mg kg(-1) dw in shortfin mako (Isurus oxyrinchus), scalloped hammerhead (Sphyrna lewini), white (Carcharodon carcharias) and ragged-tooth (Carcharias taurus) sharks. These sharks had higher THg levels than conspecifics sampled from coastal waters of the North Atlantic and North, mid-, and South Pacific, and although sampling year and shark size may play a confounding role, this result suggests the potential importance of elevated local emissions. Values of THg showed strong, species-specific correlations with length, and nearly half the remaining variation was explained by trophic position (using nitrogen stable isotopes, δ(15)N), whereas measures of foraging habitat (using carbon stable isotopes, δ(13)C) were not significant. Mercury concentrations were above the regulatory guidelines for fish health effects and safe human consumption for 88% and 70% of species, respectively, suggesting on-going cause for concern for shark health, and human consumers of shark meat.
authors.affiliation: Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario N9B 3P4, Canada. Electronic address: melissa.mckinney@uconn.edu.
authors.forename: Melissa A
authors.initials: MA
authors.lastname: McKinney
authors.affiliation: Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario N9B 3P4, Canada.
authors.forename: Kylie
authors.initials: K
authors.lastname: Dean
authors.affiliation: Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario N9B 3P4, Canada.
authors.forename: Nigel E
authors.initials: NE
authors.lastname: Hussey
authors.affiliation: KwaZulu-Natal Sharks Board, Umhlanga Rocks 4320, South Africa; Biomedical Resource Unit, University of KwaZulu-Natal, Durban 4000, South Africa.
authors.forename: Geremy
authors.initials: G
authors.lastname: Cliff
authors.affiliation: KwaZulu-Natal Sharks Board, Umhlanga Rocks 4320, South Africa; Biomedical Resource Unit, University of KwaZulu-Natal, Durban 4000, South Africa.
authors.forename: Sabine P
authors.initials: SP
authors.lastname: Wintner
authors.affiliation: KwaZulu-Natal Sharks Board, Umhlanga Rocks 4320, South Africa; Department of Agriculture, Forestry and Fisheries, Cape Town 8012, South Africa.
authors.forename: Sheldon F J
authors.initials: SFJ
authors.lastname: Dudley
authors.affiliation: Department of Agriculture, Forestry and Fisheries, Cape Town 8012, South Africa.
authors.forename: M Philip
authors.initials: MP
authors.lastname: Zungu
authors.affiliation: Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario N9B 3P4, Canada.
authors.forename: Aaron T
authors.initials: AT
authors.lastname: Fisk
mesh_terms: D000818:Animals; D004781:Environmental Exposure / Q000706:statistics & numerical data*; D020387:Food Chain; D006801:Humans; D008628:Mercury / Q000378:metabolism*; D017747:Seafood / Q000706:statistics & numerical data*; D012754:Sharks / Q000378:metabolism*; D013019:South Africa; D014874:Water Pollutants, Chemical / Q000378:metabolism*
chemical_list: D014874:Water Pollutants, Chemical; D008628:Mercury
keywords: Carbon; Elasmobranch; Isotopes; Length; Nitrogen; South Africa; Trophic position