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simulated sound from 2 MW wind turbines, but
they did not display fear behaviour (Koschinski et al.
2003). Acoustic signals increased in intensity, which
could be an exploratory behaviour. Tougaard et al.
(2009) expected no behavioural responses of seals
and porpoises to occur apart from in the immediate
vicinity of turbines, and studies by Tougaard and
colleagues (2003) and the Danish Monitoring Program
(Dong Energy et al. 2006) suggested no effects
on seals and porpoises of the wind farm in operation
at Horns Reef in Denmark. Boat traffic during
maintenance seemed to have only small effect on
porpoises (Tougaard et al. 2004). At Horns Rev,
porpoise abundance returned to preconstruction
levels shortly after the installations were finalised
(Dong Energy et al. 2006). At the Nysted wind farm
in the southern Baltic Sea, on the other hand, the
abundance of porpoises had not reached pre-construction
levels two years after construction (e.g.
Dong Energy et al. 2006). It was speculated that
the Nysted area may not be important enough for
the porpoises to remain in the area and withstand
the disturbance. Baseline data is, however, not sufficient
to firmly attribute this distribution change
neither to the presence of the wind farm nor to
the production noise. Preliminary results from the
Dutch monitoring programme at the offshore wind
farm Egmond aan Zee suggest a significant increase
in porpoise abundance after the construction
(Musalears 2009)
Several whale species (e.g. beluga whale (Delphinapterus
leucas), killer whale (Orcinus orca, humpback
whale (Megaptera novaengliae) have notably
Green turtle. Photo: Jerker Tamelander, IUCN
displayed behavioural and avoidance responses to
low frequency sounds from anthropogenic activities,
such as oil and gas exploration and boat traffic
(see Samuel et al. 2005 for references). While
habitat use patterns for whales may not generally
overlap with the relatively shallow areas used for
wind farms (apart from floating turbines), noise disturbance
might still impact behaviour, including the
migration patterns, of these species.
Conclusions
From studies of wind farms to date, there is no
evidence of marine mammals avoiding wind farms
during operation due to noise, and any long-term
avoidance behaviour of porpoises and seals should
be very local. Hence, based on current knowledge,
impacts on whole assemblages of porpoises, dolphins
and seals are considered small. Although
there are limitations in survey design, several
field studies and reviews on the subject has been
conducted. Certainty: 3. One should be extra cautious
with regard to whales, however, as impacts of
sounds on migration are not understood (See also
conclusions in 7.9., Certainty: 1).
Identifying and managing biodiversity risks and opportunities of offshore renewable energy - GREENING BLUE ENERGY 51