Trace Metal Burdens in Stranded Seals from Long Island, New York: Potential Evidence for Species Differences in Foraging

Toxic (e.g., Hg, Ag, Cd, and Pb) and essential (e.g., Se, Cu, and Fe) trace element levels were determined in liver samples from four seal species (harp seal [Phoca groenlandica], n = 35; hooded seal [Cystophora cristata], n = 7; harbor seal [Phoca vitulina], n = 34; gray seal [Halichoerus grypus], n = 10) stranding in Long Island waters between 1988 and 2004 to examine temporal and species- specific patterns in these top marine carnivores. There was no obvious trend in trace metal burdens in seal livers over this time period. Harp and hooded seals are arctic species that have only appeared in Long Island waters in recent years. Their diets are believed to include more invertebrate prey, and this was reflected in significantly higher cadmium (Cd) concentrations (mean = 5.5 to 6.3 mu g g(-1) dry weight vs. 0.5 to 1.4 mu g g(-1) for harbor and gray seals, p = 0.007). The highest mercury (Hg) burdens (> 100 mu g g(-1) dry weight) were seen in seven of the eight adult harbor seals and the only adult gray seal; four of five adult harp seals did not show elevated levels. This suggests that migratory harp seals are feeding on prey with a lower Hg burden compared to resident harbor seals that forage in the coastal environment. Copper (Cu) levels were high (70 to 105 mu g g(-1)) in a few juvenile harbor seals as predicted based on Cu- incorporating enzymes essential for growth. A few elevated silver (Ag) values (1.5 to 3.0 mu g g(-1)) were seen in the same adult harbor seals with high Hg burdens. These values may not reflect metal burdens in healthy populations as our samples were obtained from stranded animals, but there was no evidence that any of these seals died as a result of metal toxicity.