Strong increase in number of dead harbour porpoises found ... · Current situation: Strong increase...
Transcript of Strong increase in number of dead harbour porpoises found ... · Current situation: Strong increase...
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Current situation:
Strong increase in number of dead harbour porpoises found along the German Baltic coast
Fjord and Belt, Dänemark
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Stranded/By-caught harbour porpoises 1987- 2007
(FTZ)
Baltic/SH
0
20
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120
1987
1989
1991
1993
1995
1997
1999
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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?
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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
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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
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Sound-induced effects
Stress
Sound source
Audibility Behavioural reaction Masking
Impairment/ Injury
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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
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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
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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)
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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
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Stone dumping Increased ship traffic during construction /
reduced traffic during operation (no gas transport by ship) Flow noise Decommissioning!
Other activities
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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
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