strong increase in number of dead harbour porpoises found ... · current situation: strong increase...
TRANSCRIPT
Current situation:
Strong increase in number of dead harbour porpoises found along the German Baltic coast
Fjord and Belt, Dänemark
Stranded/By-caught harbour porpoises 1987- 2007
(FTZ)
Baltic/SH
0
20
40
60
80
100
120
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
Beifang
Verdacht
gestrandet
Stranded / by-caught harbour porpoises 1987-2007
Baltic / SH (FTZ Westküste)
By-caught
Potentially by-caught
Stranded
Potential causes:
By-catch Others?
Potential fields of conflict / Pipeline
Disturbance of fish Food availability (indirect)
Geophysical surveys Explosion of dumped ammunition Increased ship traffic Construction activities • Pipeline – laybarges, transport + supply vessels etc. • Service platform – pile driving, transport + supply
vessels etc. Stone dumping Decommissioning
Noise / Hearing
Underwater sound is one of the primary triggers for behavioural reactions in cetaceans
Sound and harbour porpoises
Finding prey Orientation Obstacle avoidance Communication
A functional and healthy hearing system is of primary importance for harbour porpoises
Echolocation proven
Sound-induced effects
Stress
Sound source
Audibility Behavioural reaction Masking
Impairment/ Injury
Threshold shift H
earin
g th
resh
old
Time
Intense sound can lead to a reduced hearing sensitivity (Threshold Shift, TS)
Effect can be temporary (TTS) or permanent (PTS)
PTS TTS
Noise exposure
TTS threshold in harbour porpoises at:
200 dB re 1 µPa
Underwater explosions
Photo: Kampfmittelräumdienst-SH
Shock wave
Source level: >280 dB re 1 µPa
Potential for immediate injury / deafness over greater ranges (several km)
normal
Photos: D.R. Ketten
Hearing loss
Geophysical surveys Seismic surveys to
investigate geological sub-bottom structure
High source levels:
Airgun: 260 dB re 1 µPa
Boomer: 240 dB re 1 µP
High repetition rate
Longterm / continuous use
Multiple exposures likely
Potential for hearing impairment over large ranges (up to km)
Source levels depend on sediment, diameter of pile and final depth in the ground
Typical levels: 225 – 250 dB re 1 µPa
High repetition rate > 1000 impacts per pile
Multiple exposures likely
Potential for hearing impairment over large ranges (up to km)
Pile driving
Photo: Repower
Stone dumping Increased ship traffic during construction /
reduced traffic during operation (no gas transport by ship) Flow noise Decommissioning!
Other activities
Impacts on marine mammals are likely
Noise emissions prior to / during construction most relevant
Cumulative effects of different activities
Monitoring required
Mitigation important
Conclusion
• Avoidance of sensitive periods and areas
• Visual monitoring
• Deterrent devices
• Sound reduction
• Soft start