strong increase in number of dead harbour porpoises found ... · current situation: strong increase...

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