Greening Blue Energy - BioTools For Business

should be pointed out that the reported numbers
displaced so far are relatively small in comparison
to total population levels, and hence bear no significance
to the overall populations. Moreover, it is
not clear what characteristics of wind farms caused
this avoidance behaviour. For common eiders, it has
been shown that neither noise nor movement of
the blades were the primary causes (Giullemette &
Larsen 2002, Larsen & Guillemette 2007). To speculate,
as sea ducks generally avoid flying over land,
the wind turbines could be interpreted by the birds
as patches of land, which could cause avoidance of
the area as whole.
Species occurring widespread close to human
developments, like gulls, are generally not disturbed
by wind farms, while seabirds like divers and
auks seem to be. Cormorants, gulls, and terns, on
the other hand, have been observed to use wind
turbines as resting sites between dives, and local
increases of some species within wind farm areas
have been shown (e.g. Petersen 2004, Dong Energy
et al. 2006, Fox et al. 2006, Musalears 2009). It has
also been suggested that locally enhanced abundance
of bivalves and fish around wind turbines
could enrich feeding grounds for e.g. cormorants,
gulls, and sea ducks, although effects on populations
of this are likely to be minimal (Dong Energy
et al. 2006, Fox et al. 2006).
Offshore wind farms have grown in number and
size. It has been suggested that habitat fragmentation
for birds and potential ecological effects, such
as trophic cascades as a consequence of this may
become an important issue (West & Caldow 2005).
For example, several bird species utilise temperate
ice-free areas, such as offshore banks, for wintering
and migrate to northern boreal or arctic areas
for breeding during the spring (McLaren & McLaren
1982). Furthermore, there is strong evidence that
the supply of invertebrates limits the abundance of
bird populations and determines the distribution
of the flocks (Stott & Olson 1973, Guillemette et al.
1992, Smaal et al. 2001), and populations of ducks
can subsequently influence the structure of benthic
communities (Hamilton 2000, Vaitkus & Bubinas
2001). The most numerous bird species in temperate
areas relevant for offshore wind power in northwestern
Europe and eastern North America, are
common Eider (Somateria mollissima), long tailed
duck (Clangula hyemalis), Common Scoter, (Melanitta
nigra) and Velvet Scoter (Melanitta fusca)
(Milne & Campbell 1973; Goudie & Ankney 1986;
Brager et al. 1995, Reinert & Mello 1995; Merkel
et al. 2002). In addition, other equally sensitive
but less abundant species such as divers may be
found in the same areas. Detailed species sensitivity
indexes for impacts of offshore wind farms on
seabirds are available (e.g. Garthe & Hüppop 2004,
Bright et al. 2008).
Conclusions
The risk of very broad habitat loss for sea birds (at
least, or most, for sea ducks/divers) in a wind farm
area during both construction (short term) and
operation (long term) call for special attention in
planning and development of offshore wind power.
58 GREENING BLUE ENERGY - Identifying and managing biodiversity risks and opportunities of offshore renewable energy
The severity of effects on local bird assemblages
largely depends on whether the birds find alternative
habitats or not. Evidence base from targeted
studies is comparably strong, although understanding
of longer term avoidance of areas is not established.
During construction: Certainty: 5. During
operation: Certainty: 4.
10 Aspects of decommissioning
The life span of an average offshore wind farm has
been estimated to be 25 years. The farm may then
be phased out entirely and left in place, which is the
default option alternatively it may be removed or
re-powered with new turbines. Turbines could, similarly
to oilrigs, be disassembled and recycled, discarded
to landfill, or be reconditioned and reused.
Turbines could also be partially removed or toppled.
For wind energy the resource harvested is obviously
renewable, and so it may be decided that the wind
farm should remain in operation, with continuous
maintenance and upgrading.
If the farm is completely removed, some problems
of sediment re-suspension may occur, especially
if the cables have been buried. As a consequence
sensitive habitats may again be disturbed. Future
technologies may provide better alternatives, but
current experience from oilrig decommissioning
favours explosives and cutting. Explosives would
kill most animals in the zone nearest to each turbine,
and fish with swim bladders would be most