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Exploitation of coastal fish communities by harbour porpoises Phocoena phocoena during nursing periods in German Baltic waters

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Abstract

Feeding ecology of adults and juvenile harbour porpoises in German Baltic waters during nursing period
Exploitation of coastal fish communities by harbour porpoises Phocoena
phocoena during nursing periods in German Baltic waters.
Pinzone M.1,2,*, Michel L.N.2, Gallus A.1, Brundiers K.1, Sturaro N.2, Andreasen H.3,4,
Dähne M.1, Lepoint G.2, Siebert U.3, Das K.2 and Benke H.1
1
German Oceanographic Museum, Stralsund, Germany
2
Laboratory of Oceanology - MARE, University of Liege, Liege, Belgium.
3
Institute for Terrestrial and Aquatic Wildlife Research, University of Veterinary Medicine of Hannover, Büsum,
Germany
4
DTU Aqua, National Institute of Aquatic Resources, Technical University of Denmark, Copenhagen
*
Corresponding authors. E-mail: mpinzone@ulg.ac.be
The increased number of juvenile and newborn harbour porpoise strandings along
the German Baltic coasts in summer provides evidence for a possible local calving
and nursing ground in this area. Calving and nursing habitats are the most important
areas for management purposes.
This project aimed to describe residence patterns and diet of females and calves
along the German Baltic coast, in order to achieve effective conservation measures.
Nitrogen, carbon and, for the first time, sulfur stable isotopes (δ13C, δ15N and δ34S)
were analysed in coastal species of fish and invertebrates in spring, autumn and
winter 2015/2016 and in four different areas, to assess seasonal and geographical
variation of porpoise habitat use. The structure of ecological niches was inferred
within and between communities using the SIBER model, and was compared to
results from stomach content analysis.
N, C and S values of fish and invertebrates strongly varied, seasonally and
geographically, as a consequence of environmental factors characteristic of each
sampling area. Additionally, each species presented large isotopic variability,
suggesting possible intraspecific dietary specialisations. Females δ13C and δ34S
signatures integrated both open-waters and coastal feeding, while juveniles
presented a more coastal distribution. The absence of difference in δ15N values
between age classes confirmed persistence of milk assimilation from the mothers.
Niches structures and overlaps and stomach content analysis suggested gobies
(Potamoschistus spp and Neogobius spp in particular), crabs and small coastal fish
(ex. three-spined stickleback) as the main preys of juveniles. The integration of all
three stable isotopes together permitted to well delineate even the highly dynamic
food web of the Baltic German waters, confirming the use of sulfur isotopes in marine
ecological studies.
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