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

Marine Ecology Progress Series

Jens C. Koblitz¹  Ursula K. Verfuß¹  Michael Dähne¹  Anja Gallus¹  Tobias Schaffeld¹  Kathrin Krügel¹  Martin Jabbusch¹  Anne Herrmann¹  Stefan Bräger¹  Thomas Ruf¹  Harald Benke¹ 

关键词: Cosinor analysis;    Diel rhythms;    Predation;    Phocoena phocoena;   

DOI  :  10.3354/meps11627

学科分类：海洋学与技术

来源: Inter-Research

【 摘 要 】

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.

【 授权许可】

Unknown