| Summary: | Recent observations revealed an increased abundance of the harbour porpoise in the southern part of the North Sea. Concomitant to sightings of living individuals, the number of stranded porpoises displaying lesions linked to fishing nets has also increased this last decade. The increased abundance of porpoises together with the increase in numbers of bycaught animals raised the question of possible competition between porpoises and fishermen in the North Sea. Therefore, a detailed view on harbour porpoise trophic ecology in this region is crucial for their conservation. Stomachs of the washed ashore porpoises were often empty and provided limited information on their recent diet. Another way of looking into the diet of marine mammals is the analysis of blubber. Stable isotopes ratio (d13C and d15N, SI) and fatty acid composition (20 fatty acids, FA) were analyzed in muscle and blubber of 10 freshly stranded harbour porpoises and in 60 potential prey fish from 10 species collected in the North Sea. The SI ratio and FA composition of these fish enabled a clear classification in different trophic levels and different trophic niches. The FA composition was very similar between harbour porpoise blubber and demersal fish, underlining a preferential predation on that resource for the porpoises investigated. A bias might exist for the porpoises: most of the animals were juveniles, and washed ashore during spring. Porpoises might display other feeding habits in other life stages, other periods of the year. These preliminary results however indicate the enhanced accuracy of crossing these biomarker approaches.
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