Geographical and seasonal variation of harbour porpoise (Phocoena phocoena) presence in the German Baltic Sea revealed by passive acoustic monitoring

Abstract

The harbour porpoise is the only resident cetacean species in the German Baltic Sea. Within the last several decades this harbour porpoise stock declined drastically, causing deep concern about its status. Plans of the German government for proposing Marine Protected Areas (MPAs) to implement Natura 2000 and for assessing the impact of offshore windmill constructions on the marine environment led to an increased research effort on the harbour porpoise in German waters. For the first time, long-term passive acoustic monitoring has been conducted in the German Baltic Sea from the Kiel Bight to the Pomeranian Bay from August 2002 to December 2005. Porpoise detectors (T-PODs) have been installed five to seven metres below the water surface at up to 42 measuring positions throughout the investigated area, registering the exact times of echolocation signals of passing harbour porpoises. The proportion of monitored days with porpoise detection in each quarter of the years has been analysed. A correlation of the results with the longitude of the measuring position revealed a significant decrease from west to east in the percentage of days with porpoise detections. Comparison of data gathered in the first quarters with the third quarters of the monitoring years displayed a seasonal variation with fewer days of porpoise detections in winter time than in summer time. Nevertheless, harbour porpoises have been detected year-round at most of the measuring positions in the German Baltic Sea. The present study clearly indicates a regular use of the German Baltic Sea by harbour porpoises with a geographical and seasonal variation in the usage of the German Baltic Sea. The larger numbers of harbour porpoise detections in spring to autumn compared with winter suggests that the German Baltic Sea is an important breeding and mating area for these animals.

Variation in harbour porpoise activity in response to seismic survey noise

“…Our results provide an estimate of the noise levels at which porpoise activity patterns are disrupted, and an indication of the scale of potential reductions in foraging activity [6]. Porpoise occurrence and activity is typically characterized by large seasonal and diel variability [19,31,32], as also reflected in our results (figure 2). Further studies are now required to explore the environmental conditions that drive this variation, and develop energetic models to assess whether this scale of disturbance has long-term consequences for individual energy budgets [33].…”

Using Static Acoustic Monitoring to Describe Echolocation Behaviour of Heaviside’s Dolphins (Cephalorhynchus heavisidii) in Namibia

“…The T-POD is a SAM tool which has been used extensively to monitor odontocetes (Leeney & Tregenza, 2006;Leeney et al, 2007;Philpott et al, 2007;Verfuß et al, 2007;Kyhn et al, 2008;Todd et al, 2009), including Hector's dolphins of New Zealand (Rayment et al, 2009a(Rayment et al, , 2009b, a species closely related to Heaviside's dolphins. The T-POD is a self-contained, submersible hydrophone and digital processor which recognizes and logs the echolocation clicks made by odontocetes.…”

Habitat use and conservation of an Endangered dolphin

“…The inherent directionality of sonar emissions (e.g. Au 1993) and the likelihood that dolphins are often silent (Dawson 1994, Bloom et al 1995, Nowacek 2005, but see Verfuß et al 2007, Akamatsu et al 2007) further limit the chance of detection. Also, our use of the CET ALL category (in the T-POD software) was conservative, as genuine echolocation events are often classified as DOUBTFUL or VERY DOUBTFUL (Thomsen et al 2005, Rayment et al 2009a).…”

“…For many species, this changes seasonally (e.g. Wilson et al 1997, Verfuß et al 2007). Patchiness, over a variety of scales and time periods, is a general feature of marine mammal distributions.…”