Stable isotope analysis of harbour porpoises and their prey from the Baltic and Kattegat/Skagerrak Seas

Abstract

The by-caught harbour porpoises in commercial fisheries have raised concerns over their conservation status in the Baltic region. One important aspect for management purposes is porpoise movements within the region. We measured stable isotopes in cod, herring and hagfish, species that are important prey for harbour porpoises in the Baltic region. Bone collagen in fish from the marine Kattegat/Skagerrak was significantly enriched in ¹³C compared with collagen in fish from the brackish Baltic Sea. However, despite the isotopic variation seen in their prey, we found no difference in ¹³C in harbour porpoise collagen from the two areas. In fact, only eight of 24 porpoises had isotope signatures corresponding to those estimated for the diet in the area where they were caught. Our general conclusion is that porpoises move between the Baltic and Kattegat/Skagerrak Seas. Future studies are needed to evaluate the magnitude of these movements.

Keywords:

• Baltic
• carbon isotopes
• cod
• diet
• harbour porpoises
• herring
• movements
• nitrogen isotopes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgments

We are grateful to Kerstin Lidén and her co-workers at the Laboratory of Archaeological Research in Stockholm, for help with the analyses. Uno Svensson at the Museum of Natural History in Gothenburg and Adam Stanczak at the Swedish Museum of Natural History in Stockholm kindly allowed us to take samples from the porpoise skulls. Bo Edlén and Heike Siegmund processed the samples and Fredrik Arrhenius and Ann-Christin Rudolphi at Havsfiskelaboratoriet sent us the fish. Nils Kajrup(SMHI) and Gunni Aertebjerg (DMU) helpfully provided us with salinity values.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark