Greening Blue Energy - BioTools For Business

adically among species (e.g. Thomsen et al. 2006,
Kastelein et al. 2007), and the nature and detection
level of wind turbine construction noise, including
e.g. boat traffic, pile driving, seismic surveys, is
largely unexplored. Generally, though, construction
of foundations and the laying of cables can generate
considerable acute noise (Peak 260 dB re: 1 µPa
and Peak 178 dB re: 1 µPa respectively) and could
damage the acoustic apparatus of organisms within
100 m (Enger 1981, McCauley et al. 2003, Gill 2005,
Madsen et al. 2006). Piling generates a very loud
sound of wide bandwidth (Hardyniec & Skeen 2005).
The highest energies occur in the lower frequencies
of 20 Hz to 1 kHz (Greene and Moore, 1995).
Close to the piling site this noise could cause serious
injury or even death to fish, marine mammals and
sea turtles (Hardyniec & Skeen 2005, Nowacek et
al. 2007, Snyder & Kaiser 2009). For example piling
during construction of a bridge killed fish within a
50 m radius. Experimental work has, on the other
hand, shown several fish species (including trout)
to be unaffected 10 m away from the driving of 0.7
m diameter piles (Se Snyder & Kaiser 2009 for references).
Other species of fish are predominantly
sensitive for particle motion and not pressure, and
their responses to subsea noise and vibration are
poorly known (Thomsen et al. 2006).
Mammals may suffer hearing impairment, such
as changes in hearing thresholds (e.g. Frank 2006,
Madsen et al. 2006) when exposed to piling noise
(1.5 MW, 228dB 1 µPa) at close range. Both TTS
(temporary threshold shift) and PTS (permanent
threshold shift) represent changes in the ability of
an animal to hear, usually at a particular frequency,
with the difference that TTS is recoverable after
hours or days and PTS is not. Impairment through
TTS or PTS of a marine animal’s ability to hear can
potentially have quite adverse effects on its ability
to communicate, to hear predators and to engage
in other important activities. Both TTS and PTS are
triggered by the level and duration of the received
signal. Sound can potentially have a range of nonauditory
effects such as damaging non-auditory tissues,
including traumatic brain injury/neurotrauma.
Recently, Southall et al. (2007) proposed sound
exposure criteria for cetaceans and pinnipeds composed
both of peak pressures and sound exposure
levels which are an expression for the total energy
of a sound wave. These values are currently discussed
within the scientific community as they are
based on very limited data sets with respect to noise
induced injury and behavioural response in marine
mammals. Mammals and also most fish, are, however,
likely to move away from areas of pile driving
(Figure 2, Engås et al. 1996, Popper et al. 2004).
Conclusions
Although hearing impairments could occur within
a larger radius, any mortality due to acute sound
pulses is local. Particularly mammals, but also most
large/mobile fish, will not reside in close proximity
to pile driving, and impacts of any injuries on
a species assemblage should be small (Figure 2),
provided mitigation measures are taken (see 4.5).
Temporal scale of impact is not assessed here as,
although the construction is temporary, hearing
46 GREENING BLUE ENERGY - Identifying and managing biodiversity risks and opportunities of offshore renewable energy
impairment can be permanent. There are a number
of focused studies on impacts of sound, and these
indicate that effects can vary greatly among species.
Certainty: 3. However, no studies are available
showing the extent of TTS and PTS for different
applications of mitigation measures. More studies
are clearly needed to optimise the management of
the exposure of underwater sound to marine mammals
and fish during construction.
7.2 Construction noise and avoidance by
marine mammals
Effects on animal behaviour can extend far beyond
the farm area, and pile driving may cause behavioural
changes in seals, dolphins, and porpoises
more than 20 km away (Edren et al. 2004, Tougaard
et al. 2008 and 2009, David 2006, Madsen et al.
2006, Brandt et al. 2009, Tougaard et al. 2009). Hearing
thresholds for seals and porpoises have been
identified within the MINOS Programme (Frank
2006). During wind farm construction at Nysted
wind farm in Danish part of the Baltic Sea, harbour
porpoises Phocoena phocoena abandoned the area
(with effects noted 15 km away), but at Horns Rev
wind farm in the Danish part of the North Sea where
monopiles were erected, porpoises largely returned
within a few hours after pile driving (Henriksen et al.
2003, Carstensen et al. 2006; Tougaard et al. 2009,
Dong Energy et al. 2006). The Danish monitoring
Program (Dong Energy et al. 2006) concluded that
the construction phase as a whole only had weak
effects on porpoises, while piling had distinct but