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Abstract :
[en] The Ligurian Sea, part of the Cetacean Sanctuary, is known to be a productive area hosting many marine mammal species of the Mediterranean Sea. Investigations on trophic relationship and pollutant monitoring are of primary importance for their conservation. As isotopic composition of an animal is related to that of its prey, ð13C and ð15N were measured by mass spectrometry in muscle of 12 striped dolphins (Stenella coeruleoalba), 1 bottlenose dolphin (Tursiops truncatus), 2 fin whales (Balaenoptera physalus), 3 Risso's dolphins (Grampus griseus), 1 Cuvier's beaked whale (Ziphius cavirostris) and 1 juvenile sperm whale (Physeter macrocephalus) stranded along the Ligurian coasts between 1991 and 2004. Hg concentration was also analysed in marine mammal liver by spectrometric absorption. Through ð13C and ð15N measurements, two marine mammal groups appeared: the first group characterised by high ð13C and ð15N values (mean values: -17.5‰ and 11.0‰ respectively) included the sperm whale, the bottlenose dolphin, the Risso’s dolphin and the beaked whale. The second group including striped dolphin and fin whale displayed lower mean ð13C than the first group (-18,48‰), with the fin whale showing the lowest ð15N value (8,8‰ ± 0,7). Our isotopic data are in good agreement with previously described feeding habits: the first group obviously fed at a higher trophic level and in more coastal waters associated with the continental slope while the second fed offshore, with the fin whale occupying the lowest trophic position. Hg concentrations reflected a similar pattern, with the lowest value observed in the fin whale (mean value: 0.1 µg.g-1 dw) and the highest in both the bottlenose dolphin (3769 µg.g-1 dw) and the Risso’s dolphin (1363 µg.g-1 dw). However, beside trophic position, numerous factors might be involved in Hg accumulation in marine mammals such as the age, body condition and specific metabolism.
