Stable isotope, Food web, Diet, Bioaccumulation, Dogfish, Skate, Mercury, Nitrogen Isotopes - analysis, Skates (Fish) - metabolism, Mercury - analysis, Species Specificity, Food Contamination - analysis, Atlantic Ocean, Water Pollutants, Chemical - pharmacokinetics, Dogfish - metabolism, Water Pollutants, Chemical - analysis, Mercury - pharmacokinetics, Food...