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Abstract :
[en] During the last decade, recurrent epizootics have affected harbour seal (Phoca vitulina) populations in the North Sea. Recent data on their trophic habits and pollutant levels are of primary importance for their conservation. As isotopic composition of an animal is related to that of its prey, δ13C and δ15N were measured by mass spectrometry in the muscles of 66 harbour seals beached along the coasts of France (n = 10), Belgium (n = 30) and Netherlands (n = 26) between 1994 and 2004. Trace metals concentrations (Zn, Cu, Fe, Cd, Hg and Se) were also determined in liver, kidney and muscles by Inducted Plasma Spectrometry. δ13C and δ15N values remained similar between harbour seals from France (-15.7 0/00; 18.7 0/00, respectively), Belgium (-15.7 0/00; 19.0 0/00, respectively) and Netherlands (-14.7 0/00; 18.7 0/00, respectively). These data are in good agreement with their coastal and piscivorous life style. Isotopic value remained similar between males and females and between body conditions. Hg levels were significantly higher in seals from the southern North Sea when compared to previously published data from seals collected in Norway, probably due some geographical differential exposure. Hepatic Hg was positively correlated to hepatic Se, both increasing with the length of the seals. Such a relationship reflected an age accumulation process coupled to a detoxication mechanism involving antagonism between Hg and Se in the liver. No relationship between stable isotopes and Hg and Cd levels was observed. Increasing Zn and Hg hepatic levels were observed with degrading body condition of the harbour seals, which is reflected by decreasing blubber thickness and high hepatic to total body mass ratio. These observations tend to indicate a global redistribution of trace metals from muscle and blubber to liver, as a result of protein and lipid catabolism linked to disease and starvation.
