1. ECOLOGICAL IMPACT ASSESSMENT
14 Marine Scientist No.48 August 2014
W
orking in the off-
shore wind sector
over the past few
years has been both
interesting and challenging. Be-
cause of the novel nature of the
industry, the increased scale of
developments and the uncertain-
ties associated with offshore wind
farm construction and operation,
the level of information required
to undertake Ecological Impact
Assessment (EcIA) has increased
considerably since the first off-
shore wind farms built in the
first of the Crown Estate leasing
rounds.
One of the key impacts on
fish ecology from offshore wind
farms is underwater noise as-
sociated with construction, par-
ticularly piling of foundations
for offshore structures (e.g.
turbines and substations). In
extreme cases, piling noise can
lead to injury or mortality to
fish, though only in close prox-
imity to piling operations and
the use of standard soft start
procedures reduces the poten-
tial for injury effects.
The two key issues relating to
the potential effects of underwa-
ter noise on fish are disturbance
of spawning habitats and disrup-
tion of fish migration to/from
spawning habitats. I have worked
on these two issues for a number
of offshore wind farm projects
including Triton Knoll, Hornsea
Projects One and Two and Atlan-
tic Array.
Fish spawning
One of the most important
factors when undertaking impact
assessments on fish spawning
habitats is accurate, reliable base-
line characterisation data. These
can help to define the extents of
spawning habitats and the timing
of peak spawning for key species.
This ensures that impact assess-
ments are as accurate as possible
while maintaining an appropriate
level of precaution.
For assessing impacts on fish
spawning, we have used site spe-
cific survey data and existing
baseline data, including a range
of literature and data sources,
to refine the broad scale spawn-
ing and nursery habitats mapped
across the UK (e.g. Coull et al.
1998; Ellis et al. 2012). One of the
more sensitive fish species to un-
derwater noise is herring (Clupea
harengus). This species has specif-
ic habitat requirements (eggs are
laid on gravelly substrates) and is
known to have high site fidelity in
their spawning grounds.
Herring is also a prey species
for a range of bird and marine
mammals and therefore plays a
key ecological function, increas-
ing the importance of avoiding
population level effects on this
species. As such, it is important
when carrying out impact as-
sessments to try to delineate the
spawning habitats that are used
most frequently. Information
from the fishing industry and
Ecological Impact
Assessment for
Offshore Wind Farms
Dr Kevin Linnane is a Chartered Marine Scientist
and Senior Marine Ecologist with RPS, an interna-
tional consultancy providing advice and technical
services for the offshore renewables industry, the
exploration and production of oil, gas and other nat-
ural resources and offshore and coastal infrastruc-
ture projects. As a specialist in Ecological Impact
Assessment for offshore wind farm developments,
Kevin has considerable experience in dealing with
a range of marine ecological issues, with a particu-
lar focus on subtidal benthic habitats and fish and
shellfish ecology. Kevin works within the RPS marine
ecology team comprising ten marine scientists from
a range of backgrounds and covering a variety of
technical disciplines.
ECOLOGICAL IMPACT ASSESSMENT
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2. No.48 August 2014 Marine Scientist 15
an understanding of the sedi-
ment composition can be useful
in delineating these areas. One
of the most reliable indicators of
herring spawning habitats is the
presence of high abundances of
herring larvae and data from the
International Herring Larvae
Survey (IHLS)1
are often used to
delineate these habitats.
Once there is agreement on
the location and extents of spawn-
ing habitats and the timing of
spawning, underwater noise mod-
elling is used to estimate the dis-
tance at which behavioural effects
(i.e. avoidance) may occur during
piling operations, with a view to
quantifying the magnitude of the
effect on spawning fish (i.e. the
degree of overlap with spawning
habitats, numbers of spawning
seasons affected, etc.).
This is a developing field and
there are therefore uncertain-
ties associated with these mod-
els, with different approaches to
modelling and different criteria
used to estimate the ranges at
which behavioural effects may
occur. Additionally, there are un-
certainties about the behavioural
responses of fish to underwater
noise with the level of behav-
ioural disturbance dependent
on a number of factors, such as
the type of fish, its sex, age and
condition, as well as other stres-
sors to which the fish is or has
been exposed. The response of
the fish will also probably de-
pend on the reasons and drivers
for the fish being in the area. For
example, spawning may poten-
tially increase the desire for the
fish to remain in the area despite
the elevated noise levels.
Because of these uncertainties,
an element of precaution needs to
be included in these assessments
(e.g. in relation to fish behavioural
response to noise), whilst ensur-
ing that the assessment is realistic
when also considering the addi-
tional precaution inherent in the
‘Rochdale Envelope’ approach
(i.e. assessing the maximum ad-
verse scenario for the project2
).
Fish migration
Impacts on fish migration as
a result of underwater noise from
piling operations may also occur.
Although many fish species mi-
grate in the marine environment
(e.g. to feeding or nursery habi-
tats), diadromous fish species (fish
that migrate between fresh and salt
water) are particularly sensitive be-
cause their life cycles require them
to move between the sea and riv-
ers/estuaries at particular times of
year. Impacts on these species can
be more difficult to predict due to
considerable uncertainties associ-
ated with the at-sea behaviour and
their distribution.
Most of the information avail-
able on these species is from rivers
and estuaries, with records made
while they are migrating to/from
spawning habitats. Records of di-
adromous fish species further off-
shore are sporadic, making it dif-
ficult to predict accurately where
these species are likely to occur
relative to offshore wind farms. As
a result of these uncertainties, im-
pact assessment on these species
has generally focused on the po-
tential for underwater noise from
piling operations to create barri-
ers with the coast during key mi-
gration periods. Reliable data on
peak migration periods for migra-
tory fish species are more readily
available than data on at-sea be-
haviour or distribution.
Dr Kevin Linnane,
a specialist in Ecological
Impact Assessment
for offshore wind farm
developments, writes
about the exciting
challenges of his work
Atlantic white-
sided dolphins
Bottlenose
dolphin
1
The IHLS is a long-term (1967-present)
survey programme coordinated by ICES,
with the main objective to provide esti-
mates of herring larval abundances in the
North Sea and surrounding area, to pro-
vide a relative index of changes of the her-
ring spawning stock biomass.
2
The ‘Rochdale Envelope’ is an approach
to consenting and environmental impact
named after two UK planning cases (R. v
Rochdale MBC ex parte Milne (No. 1) and
R. v Rochdale MBC ex parte Tew [1999] and
R. v Rochdale MBC ex parte Milne (No. 2)
[2000]). It allows a project description to be
broadly defined, within a number of agreed
parameters, giving some flexibility while a
project is in the early stages of development
(i.e. during the consenting process).
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3. ECOLOGICAL IMPACT ASSESSMENT
16 Marine Scientist No.48 August 2014
Because there are uncertain-
ties associated with the behaviour-
al responses of fish to underwater
noise, and because many migra-
tory fish species are also features
of Special Areas of Conservation,
designated under the EC Habitat
Directive, the precautionary prin-
ciple must also be applied, i.e.
consent cannot be given unless it
is ascertained that there will be no
adverse effect on the integrity of
the site. It is therefore important
to ensure assessments are under-
taken in a robust manner, based
on the best available science, while
also ensuring that an adequate
level of precaution is assumed
within the assessment to comply
with the Habitats Directive.
Mitigation
In some circumstances, there is
a need for mitigation to reduce im-
pacts of underwater noise on ma-
rine species (including fish spawn-
ing and migratory fish). In the UK,
this has taken the form of seasonal
restrictions on piling operations,
though in Germany noise reduc-
tion technologies (e.g. bubble cur-
tains) are routinely used to reduce
noise levels associated with off-
shore wind farm piling operations
(though this mitigation is designed
for marine mammals). More re-
cently, due to the increased size of
offshore wind farms and the great-
er certainty associated with map-
ping fish spawning habitats, it has
been possible to manage piling op-
erations within offshore wind farm
sites to ensure piling, in certain
parts of wind farm sites, is either
avoided or undertaken at lower
hammer energies during certain
periods (e.g. during fish spawning
or migration).
We continue to work with a
number of offshore wind farm
developers to reduce impacts on
fish by scheduling construction
to ensure impacts on fish species
are minimised or, where possible,
avoided completely. This will in-
volve compilation of reliable base-
line data on location and timing
of spawning/migration and work-
ing with engineers to ensure that
construction operations (includ-
ing piling operations) are spa-
tially and temporally managed to
minimise noise disturbance from
piling in the vicinity of the most
sensitive habitats during the peri-
ods of highest sensitivity.
This approach also takes into
account more detailed informa-
tion on the ground types across
the offshore wind farm site (and
therefore the hammer energies
likely to be required in certain
areas) and more detailed project
design information (i.e. founda-
tion types and locations) that may
not have been available at the time
of consenting. This provides one
practical solution to mitigating the
effects of piling-related underwa-
ter noise on fish populations,
whilst ensuring that construction
on large offshore wind farms does
not cease, causing significant de-
lays to project programmes and
cost implications. 
References
Bexton, S., Thompson, D., Brownlow,
A., Barley, J., Milne, R. and Bidewell, C.
(2012) Unusual mortality of pinnipeds in
the United Kingdom associated with heli-
cal (corkscrew) injuries of anthropogenic
origin. Aquatic mammals 38(3): 229–240.
Coull, K.A., Johnstone, R. and Rogers, S.I.
(1998) Fishery Sensitivity Maps in British
Waters. Published and distributed by UK-
OOA Ltd.
Ellis, J.R., Milligan, S.P., Readdy, L., Taylor,
N. and Brown, M.J. (2012) Spawning and
Nursery Grounds of Selected Fish Spe-
cies in UK Waters. Sci. Ser. Tech. Rep.,
Cefas, Lowestoft, 147: 56 pp.
Harwood, J., King, S., Schick, R., Dono-
van, C. and Booth, C. (2014) A Protocol
for Implementing the Interim Population
Consequences of Disturbance (PCoD)
Approach: Quantifying and Assessing
the Effects of UK Offshore Renewable
Energy Developments on Marine Mam-
mal Populations. Report number SMRUL-
TCE-2013-014. Scottish Marine and Fresh-
water Science, 5(2).
A piling vessel
installing an
offshore wind
turbine
foundation
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4. No.48 August 2014 Marine Scientist 17
RPS Marine Mammal Project Team
Potential impacts on marine mammals from offshore development are often a contentious
issue. Navigating through various technical reports, legislative frameworks, and possible con-
flicts during consultation can present a minefield to the consultant. The RPS marine mammal
project team has met these challenges head on and has exponentially increased their capabil-
ity in marine mammal ecology and impact assessments through training, hands on experience,
and collaboration and networking with scientific institutes.
The team comprises marine mammal ecologists, underwater acousticians, GIS technicians
and environmental practitioners. Our project experience has spanned different sectors, includ-
ing offshore renewables, oil and gas and ports and harbours. All aspects of marine mammal
related capabilities can be covered, including marine mammal and acoustic surveys, data
analysis and interpretation, underwater noise modelling, impact assessment, Habitats Regula-
tion Assessment reports, European Protected Species risk assessments and licence applica-
tions, and mitigation and monitoring design.
In the last year RPS has also formed a Marine Mammal Working Group, led by Dr Tessa
McGarry and Tamara Al-Hashimi. Tessa and Tamara have considerable experience in EcIA, and
have acted as marine mammal advisors for a number of key offshore wind farm and oil and
gas projects. The Working Group, made up of members in the UK, America and Australia, aims
to ensure that RPS specialists are up to speed on the most recent developments around the
globe with regard to key issues and emerging topics.
To achieve this, members of the Marine Mammal Working Group regularly attend seminars,
conferences and workshops on marine mammal related topics and keep abreast of current
scientific research in this area. For example, we are following the latest scientific research relat-
ing to potential behavioural effects of subsea noise on marine mammals and in particular the
forthcoming PCoD (Population Consequences of Disturbance) framework, which will provide
a useful tool for assessing population level effects (Harwood et al., 2014). Similarly, we are
monitoring the work on corkscrew injury that has arisen out of a nationwide concern that marine
mammals (in particular seals) may be vulnerable to injury from collision with vessels that use
ducted propellers (Bexton et al., 2012). The Marine Mammal Working Group maintains strong
links with academic institutions and technical specialists and often works in collaboration with
recognised experts in the field.
Harbour seal
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