Pelagic Ecology Construction Assessment
Water Quality Induced Impacts
Numerical water quality modelling predicts that worst-case levels of suspended solids at all representative pelagic
sensitive receivers shall be significantly below the impact evaluation criterion of 50 mg/l criterion that was set by
Government. Accordingly, no adverse impacts upon fish, marine mammals or other pelagic species are anticipated.
The assessment can be viewed in the water quality section --->>>
Noise Impacts
A comprehensive review and assessment of underwater noise effects on marine mammals and fish has been
conducted by Thomsen et al (2006) based on wind farm developments in the North Sea. The following assessment
is largely based on this recent work.
Studies have shown that European harbour porpoise Phocoena phocoena communicate with a range of sounds, and
can hear in the range of 16 – 140 kHz (Kastelein et al., 2002). The sounds emitted by this species – in the same
taxonomic Family as the finless porpoises resident in HKSAR waters – have been categorised as follows based on
Verboom and Kastelein (1995):
Sonar clicks have been found to be the main sound emitted by the harbour porpoise (ibid.). Similarly, studies of the
finless porpoise suggest that it produces similar sonar clicks at a peak frequency of 142 kHz (Goold & Jefferson,
2002).
As regards potential construction phase impacts, marine dredging / jetting works and large marine vessels typically
emit sound in the range of 0.02 to 1 kHz (Goold & Jefferson, 2002; Popper et al, 2003). Medium sized offshore support
and supply vessels typically generate noise at frequencies between 0.02 to 10 kHz (Richardson et al. 1995), with
marine vessel noise measured near the Urmston Road in western HKSAR waters at 2.5 kHz (Würsig and Greene,
2002). These underwater noises are thus generally below the hearing range of finless porpoises, and certainly
below the documented peak hearing range of ~140 kHz for porpoises.
Construction noise levels are also generally below the 8 - 90 kHz hearing range of the Indo Pacific Hump-backed
dolphin, Sousa chinensis reported by Richardson et al (1995), although this species is uncommon outside its
preferred estuarine habitat and thus a very uncommon sighting in the Study Area.
It is clear from past AFCD visual and acoustic studies, and the present BMT visual study, that finless porpoises and
other cetaceans do not use the east Hong Kong proposed Wind Farm area to a high extent (for example, Jefferson et
al., 2002; AFCD, 2005, 2007). The foundation structures of the proposed Wind Farm are to be installed using the
relatively non-noisy suction can foundation system. While there may be some avoidance of the immediate area (within
about 200 to 500 m) during construction (based on data from various reports on European harbour porpoises), no
adverse impacts on marine mammals are anticipated during marine construction activities.
The hearing ranges of fishes has been studied less, although a hearing range for fish of 30 Hz to 1 kHz is generally
agreed, recognizing that some species can hear sound below or above this range (Popper et al, 2004). Accordingly,
noise from construction activities may affect fishes in the Study Area.
Construction activities will lead to an increase in the number of marine vessels at the proposed wind farm from the
present (low) baseline average of 20 vessels / day, and thus marine vessel activity shall be the primary noise source
for fishes. Construction marine traffic will include the heavy lift vessel for turbine installation, a dedicated cable laying
vessel and a variety of tugs and work boats to support operations. Work at the proposed wind farm will occur in
concentrated periods and during the busiest days up to 15 vessels may be operating (BMT, 2007). Although this would
effectively create a short term doubling of vessels, the marine traffic density would be less than 0.2% that of Hong
Kong’s busier fairways.
The seabed of the proposed wind farm is exposed and offers no habitat for fin fishes, while no turbine installation
activities shall be in proximity to reef fish habitat at the Ninepin Islands or Basalt Island. Given these considerations
and the low overall marine traffic volume associated with construction, no significant adverse impacts on fishes are
anticipated.
Water Quality Induced Impacts
Numerical water quality modelling predicts that worst-case levels of suspended solids at all representative pelagic
sensitive receivers shall be significantly below the impact evaluation criterion of 50 mg/l criterion that was set by
Government. Accordingly, no adverse impacts upon fish, marine mammals or other pelagic species are anticipated.
The assessment can be viewed in the water quality section --->>>
Noise Impacts
A comprehensive review and assessment of underwater noise effects on marine mammals and fish has been
conducted by Thomsen et al (2006) based on wind farm developments in the North Sea. The following assessment
is largely based on this recent work.
Studies have shown that European harbour porpoise Phocoena phocoena communicate with a range of sounds, and
can hear in the range of 16 – 140 kHz (Kastelein et al., 2002). The sounds emitted by this species – in the same
taxonomic Family as the finless porpoises resident in HKSAR waters – have been categorised as follows based on
Verboom and Kastelein (1995):
- Low frequency sounds at 1.4 – 2.5 kHz for communication
- Sonar-clicks (echolocation) at 110 – 140 kHz
- Low-energy sounds at 30 – 60 kHz
- Broadband signals at 13 – 100 kHz
Sonar clicks have been found to be the main sound emitted by the harbour porpoise (ibid.). Similarly, studies of the
finless porpoise suggest that it produces similar sonar clicks at a peak frequency of 142 kHz (Goold & Jefferson,
2002).
As regards potential construction phase impacts, marine dredging / jetting works and large marine vessels typically
emit sound in the range of 0.02 to 1 kHz (Goold & Jefferson, 2002; Popper et al, 2003). Medium sized offshore support
and supply vessels typically generate noise at frequencies between 0.02 to 10 kHz (Richardson et al. 1995), with
marine vessel noise measured near the Urmston Road in western HKSAR waters at 2.5 kHz (Würsig and Greene,
2002). These underwater noises are thus generally below the hearing range of finless porpoises, and certainly
below the documented peak hearing range of ~140 kHz for porpoises.
Construction noise levels are also generally below the 8 - 90 kHz hearing range of the Indo Pacific Hump-backed
dolphin, Sousa chinensis reported by Richardson et al (1995), although this species is uncommon outside its
preferred estuarine habitat and thus a very uncommon sighting in the Study Area.
It is clear from past AFCD visual and acoustic studies, and the present BMT visual study, that finless porpoises and
other cetaceans do not use the east Hong Kong proposed Wind Farm area to a high extent (for example, Jefferson et
al., 2002; AFCD, 2005, 2007). The foundation structures of the proposed Wind Farm are to be installed using the
relatively non-noisy suction can foundation system. While there may be some avoidance of the immediate area (within
about 200 to 500 m) during construction (based on data from various reports on European harbour porpoises), no
adverse impacts on marine mammals are anticipated during marine construction activities.
The hearing ranges of fishes has been studied less, although a hearing range for fish of 30 Hz to 1 kHz is generally
agreed, recognizing that some species can hear sound below or above this range (Popper et al, 2004). Accordingly,
noise from construction activities may affect fishes in the Study Area.
Construction activities will lead to an increase in the number of marine vessels at the proposed wind farm from the
present (low) baseline average of 20 vessels / day, and thus marine vessel activity shall be the primary noise source
for fishes. Construction marine traffic will include the heavy lift vessel for turbine installation, a dedicated cable laying
vessel and a variety of tugs and work boats to support operations. Work at the proposed wind farm will occur in
concentrated periods and during the busiest days up to 15 vessels may be operating (BMT, 2007). Although this would
effectively create a short term doubling of vessels, the marine traffic density would be less than 0.2% that of Hong
Kong’s busier fairways.
The seabed of the proposed wind farm is exposed and offers no habitat for fin fishes, while no turbine installation
activities shall be in proximity to reef fish habitat at the Ninepin Islands or Basalt Island. Given these considerations
and the low overall marine traffic volume associated with construction, no significant adverse impacts on fishes are
anticipated.
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