Abstract

The harbour, or common, porpoise (Phocoena phocoena) is the smallest cetacean inhabiting temperate to cold waters throughout the northern hemisphere. Due to its occurrence mainly but not exclusively in coastal or shelf waters, the porpoise is threatened by a variety of anthropogenic influences (Hutchinson et al. 1995, Kaschner 2001, Scheidat and Siebert 2003), including by-catch in fishery (Kock and Benke 1996, IWC 1997, Vinther 1999, Lockyer and Kinze 2000) and habitat degradation due to e.g. chemical pollution (Jepson et al. 1999, Siebert et al. 1999). The harbour porpoise is the only cetacean species regularly found in both the German North and Baltic Seas (Reijnders 1992, Benke and Siebert 1994, Schulze 1996, Benke et al. 1998, Hammond et al. 2002, Siebert et al. accepted).

Until recently, very little data existed on the distribution of and habitat use by harbour porpoises in German waters. Most information on distribution and population numbers in the German North and Baltic Seas was based on results of the SCANS (Small Cetacean Abundance in the North Sea and Adjacent Waters) survey of July 1994 (Hammond et al. 1995, Hammond et al. 2002). Unfortunately, the SCANS investigation did not cover some areas of the German Exclusive Economic Zone (EEZ), such as the region east of the island of Rgen close to the Polish border in the Baltic Sea, and some parts off the East Friesian Islands between the estuary of the river Elbe and the Dutch border in the North Sea.

Due to this gap in knowledge, it was necessary to investigate German waters in respect of distribution, density as well as habitat use of harbour porpoises in order to assess further anthropogenic influences and their cumulative effects, e.g. the planned construction of offshore farms. Furthermore, since noise pollution is considered a particularly important threat in this respect, more information on the animals hearing capabilities is required to facilitate the establishment of a solid baseline for appropriate mitigation measures.

This paper summarises four parts of the MINOS1 project which dealt with harbour porpoises:
1. Investigation of density and distribution patterns of harbour porpoises (Phocoena phocoena) in the German North and Baltic Seas.
2. Investigations on the habitat use of harbour porpoises in the North and Baltic Seas using autonomous echo-location click detectors (T-PODs).
3. Intercalibration of different methods for observing and counting harbour porpoises (Phocoena phocoena) in the whale sanctuary in the Nationalpark of the Schleswig-Holstein Wadden Sea.
4. Study on the impact of offshore windmill-related sound emissions on the auditory system of marine mammals in the German North and Baltic Seas.