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Marine Ecology Progress Series

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MEPS 547:257-272 (2016)  -  DOI:

Diel and seasonal patterns in acoustic presence and foraging behaviour of free-ranging harbour porpoises

Tobias Schaffeld1,2,3,*, Stefan Bräger1,4, Anja Gallus1, Michael Dähne1,3, Kathrin Krügel1, Anne Herrmann1, Martin Jabbusch1, Thomas Ruf5, Ursula K. Verfuß1,6, Harald Benke1, Jens C. Koblitz1,7

1German Oceanographic Museum, Katharinenberg, 18439 Stralsund, Germany
2University of Natural Resources and Life Sciences, 1180 Vienna, Austria
3Institute for Terrestrial and Aquatic Wildlife Research, University of Veterinary Medicine Hannover, Foundation, 25761 Büsum, Germany
4International Seabed Authority, Kingston, Jamaica
5Research Institute of Wildlife Ecology, University of Veterinary Medicine Vienna, 1160 Vienna, Austria
6SMRU Consulting, Scottish Oceans Institute, St. Andrews KY16 9SR, UK
7BioAcoustics Network, 18439 Stralsund, Germany
*Corresponding author:

ABSTRACT: A temporal and geographical analysis of echolocation activity can give insights into the behaviour of free-ranging harbour porpoises Phocoena phocoena. Seasonal and diel patterns in the presence and foraging activity of harbour porpoises were investigated based on a year-long passive acoustic monitoring data set recorded at 5 sites in the western Baltic Sea. Diel patterns in detection rates were found at 4 sites. A year-round rhythm in presence, however, was found at only 1 station, whereas the other 3 stations showed diel rhythms for 2 to 3 seasons. Three of the sites showed diel patterns in foraging sequences on a seasonal level, but no station showed such patterns for the complete year of investigation. Both diurnal and nocturnal patterns in harbour porpoise detections were observed, indicating that diel rhythmic behaviour is more complex than previously reported. In contrast, foraging behaviour showed only nocturnal rhythms. Owing to the limitations in passive acoustic monitoring, all categorized foraging sequences are a minimum estimate. Therefore, classified foraging sequences are most likely pelagic foraging, while bottom grubbing could have been missed. Differences in the occurrence of foraging sequences between station, season and time of day lead to the assumption that the long-term echolocation diel patterns of porpoises strongly depend on the temporal changes in food availability and composition within a certain habitat. Echolocation behaviour of foraging porpoises is strongly influenced by seasonally available prey resources, which require adaptive foraging strategies. Therefore, owing to seasonal variations, analyses of diel patterns need to be conducted over sufficiently long time periods and large geographic scales to allow generalized interpretation of the findings. Consequently, no general conclusion regarding diel rhythms in harbour porpoise echolocation was found. We hypothesize that porpoises in the study area alternate between foraging on benthic prey in shallow waters at daytime and in the pelagic in deeper waters at night.

KEY WORDS: Cosinor analysis · Diel rhythms · Predation · Phocoena phocoena

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Cite this article as: Schaffeld T, Bräger S, Gallus A, Dähne M and others (2016) Diel and seasonal patterns in acoustic presence and foraging behaviour of free-ranging harbour porpoises. Mar Ecol Prog Ser 547:257-272.

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