From museum to field and necropsy sampling: a long history of seals and porpoises in the North Sea

摘要: The average temperature of the North Sea has risen twice as fast as the oceans of the world with already detectable consequences to the ecosystem. The North Sea is a critical habitat to different marine mammal species including the grey seal, Halichoerus grypus, the harbour seal Phoca vitulina, and the harbour porpoise, Phocoena phocoena. Long-term approach of their feeding ecology is crucially needed to understand their response in term of global changes and management of their population. A multi-tracer approach (THg and Se; 13C, 15N, 34S values) was applied on harbour seals and grey seals (blood; German and Scottish coasts, n=174 and n=80, respectively) during different time periods (from 1900 to 2017). Additionally, the same tracers were analysed in harbour seals (hair; from 1930 to 2017) from the Natural History Museum of Stockholm (n =10), free-ranging and stranded harbour seals from the North Sea (German and Belgian coasts, n=40 and n=6, respectively). Data acquired previously on harbour porpoises from the southern part of the North Sea were integrated (muscle; 1994-2018, n=188). Our multi-tracer approach revealed: (1) an increase of trophic niche size and foraging distribution (from inshore to offshore), an increase of foraging resource items (more flatfish and less sandeels) for Scottish grey seals over time; (2) long-term changes having affected the North Sea are reflected in hair collected from harbour seals. We found a linear concomitant increase of THg and 13C values, reflecting a higher exposure combined to a more intense use of wind farm locations for foraging activities. Wind farms areas …