Harbour porpoise (Phocoena phocoena Linnaeus, 1758) entering the Weser river after decades of absence

Abstract

Since 2005, harbour porpoise (Phocoena phocoena) sightings in the lower course of the river Weser have been reported after decades of apparent absence. The aim of this study was to document the habitat use and distribution using an opportunistic sightings scheme (2007–2010) and two acoustic click detectors (March–July 2010). Seventy-nine sightings with 125 animals have been reported. Most sightings occurred during April (44%) and May (35.7%). Acoustic data at Weser river km (RKM) 51 revealed 413 harbour porpoise click trains. Sightings indicate a strong seasonality. C-POD data at RKM 51 indicated a presence 7 km upstream (south) of the southernmost sighting on 18 days. Acoustic data includes typical click trains associated with feeding (n=34) and communication (n=29). Ramming of sheet piles in 2010 at Brake (RKM 42) may have deterred porpoises from migrating further upstream. The reasons why the small cetaceans nowadays enter the Weser are not clear. They may follow anadromous fish shoals such as herring, smelt and twaite shad representing the most dominant species by biomass in April/May. However, due to size and life-history considerations of these fish, it appears unlikely that a single fish species attracts porpoises into the river.

Keywords:

• Harbour porpoise
• Phocoena phocoena
• prey
• C-POD
• Weser river

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

Acknowledgements

We thank all participants of the sightings scheme. We are grateful to the Waterways and Shipping Administration (WSA Bremerhaven) for the use of their ships for deploying and retrieving C-PODs and technical support. We acknowledge the Chelonia team, especially Nick Tregenza, for their support. We gratefully acknowledge cooperation with the County Administration Wesermarsch, especially Martin Stein for his personal commitment. We thank Ulrike Kirsch and Ulrich Karlowski for their help and advice as well as Holger Jureczko for assisting in media and field work. We thank Niedersachsen Ports, Brake for providing data on ramming activities at Brake port and the State Office for Consumer Protection and Food Safety, Hannover for providing available fish data. The project was supported by Deutsche Umwelthilfe (German Environmental Aid, DUH).

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