| Summary: | Great concern raised from the populations decline observed for the harbour porpoises in the North Atlantic but Norwegian populations remain poorly characterized. Trace elements concentrations (Zn, Cu, Cd, Se, total Hg) have been determined in liver, kidney and muscle of 23 harbour porpoises (Phocoena phocoena) caught in fishing nets along the Norwegian coast. Sources of variation have been examined with a special interest on geographic location and diet modifications analysed through stable isotopes of carbon (δ13C) and nitrogen (δ15N). This study further intend to complete previous feeding ecology knowledge with a combined approach of stable isotopes ratios and metals concentrations as dietary tracers. Norwegian porpoises display mean hepatic concentrations of Zn, Cu and total Hg (96 ± 18; 25 ± 6 15 ± 10 µg.g-1dw respectively) among the lowest in the North-Atlantic. These results suggest that porpoises from this region are less exposed to these metals than others sites such as the North Sea. The low burdens of certain metals (Zn, Cu, Hg) observed make the Norwegian populations suitable to be used as reference level for future ecotoxicological studies on this species. However, renal Cd concentrations (6.7 ± 4.1µg.g-1dw) are twice higher than those from the Southern North Sea. They probably reflect dietary modifications of the porpoises through their range. The low isotopic composition (mean muscle values: d13C=-18.5 ± 0.6 0/00 and δ15N=13.5 ± 1.2 0/00) suggests that Norwegian porpoises feed on more oceanic preys as confirmed by variations of hepatic Hg and renal Cd concentrations. Given that teutophagous marine mammals present higher concentrations of Cd than piscivorous ones. The results obtained lead to the conclusion that the Norwegian porpoises rely on more oceanic squids than those from the North Sea.
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