BURBO BANK EXTENSION OFFSHORE WIND FARM ... 1 Burbo Bank Extension offshore wind farm Supplementary...

Hearing Document 1 – Burbo Bank Extension Offshore Wind Farm Order page 1

BURBO BANK EXTENSION OFFSHORE WIND FARM

DONG Energy Burbo Extension (UK) Ltd.

Appendix 6 – AGREED Statement of Common Ground with Natural Resources Wales and Natural England on red-throated diver

for the proposed Burbo Bank Extension Offshore Wind Farm Order

Planning Inspectorate Reference: EN010026

Version: Final

13 March 2014 (submitted for Deadline VI (13 March 2014)

AGREED Supplementary Statement of Common Ground with Natural England and Natural Resources Wales regarding red throated divers

Appendix 6

2

Burbo Bank Extension Offshore Wind Farm


Prepared by: NIRAS Consulting and Allen Risby (Environmental Manager, DONG Energy)

Checked by: Allen Risby (Environmental Manager, DONG Energy) and Stuart Livesey (Consents Project Manager, DONG Energy)

Accepted by: Stuart Livesey (Consents Project Manager, DONG Energy)

Approved by: Ferdinando Giammichele (Project Development Manager, DONG Energy)

Revision history

Version Date Author History

Version 1 22nd

January 2014 NIRAS Consulting Draft produced for comment

Version 2 3rd February 2014

Allen Risby (Environmental Manager, DONG Energy)

Updated with comments from Natural England

Version 3 4th February 2014


Updated with comments by DONG Energy

Version 4 28th February 2014


Updated for comment by Natural England and Natural Resources Wales

Version 4a 6th March 2014


updated by DONG Energy to include reference to studies by Kaiser et al (2005) and Topping & Petersen (2011)

Version 5 10th March 2014


Updated with comments from Natural England and Natural Resources Wales

V5 Review 11th March 2014

Stuart Livesey (Consents Project Manager, DONG Energy)

Review and acceptance

Final 12th March 2014

Ferdinando Giammichele (Project Development Manager, DONG Energy)

Final review and sign off

Burbo Bank Extension Offshore Wind Farm

c/o DONG Energy Burbo Extension (UK) Ltd.

33 Grosvenor Place

London

United Kingdom

SW1X 7HY

Telephone +44 020 7811 5235

Website: www.burbobankextension.co.uk

Email: [email protected]

Name & Registered Office:


Watson, Farley & Williams LLP

15 Appold Street

London

United Kingdom

EC2A 2HB

Company No. 07307131

Produced by DONG Energy Wind Power (UK) Ltd., March 2014

© Copyright DONG Energy Wind Power (UK) Ltd., 2014. No part of this publication may be reproduced by any means without prior permission from DONG Energy Wind

Power (UK) Ltd. Text is correct at the time of writing. Every effort has been made to ensure the accuracy of the material published. However, DONG Energy Wind Power (UK)

Ltd. is not liable for any inaccuracy.

http://www.burbobankextension.co.uk/

mailto:[email protected]

Burbo Bank Extension offshore wind farm Supplementary SOCG between DONG Energy and Natural England and Natural Resources Wales with regard to impacts on wintering red-throated diver (Liverpool Bay / Bae Lerpwl SPA)

Version 1, 22nd January 2014 DRAFT

Version 2 with comments from Natural England

Version 3 with updated comments by DONG Energy, 4th February 2014

Version 4, 28th February 2014, updated for comment by Natural England and Natural Resources

Wales

Version 4a, 6th March 2014, updated by DONG Energy to include reference to studies by Kaiser

et al (2005) and Topping & Petersen (2011)

Version 5, 10th March 2014, with comments from Natural England and Natural Resources

Wales

Contents 1. Introduction .................................................................................................................................... 3

2. Red-throated diver .......................................................................................................................... 3

Conservation objectives ...................................................................................................................... 3

Favourable condition .......................................................................................................................... 4

Data analysis ....................................................................................................................................... 5

Interaction ........................................................................................................................................... 6

Magnitude of displacement (N) .......................................................................................................... 6

Proportion of birds lost to the SPA (P) ................................................................................................ 8

Conclusions ....................................................................................................................................... 16

References ............................................................................................................................................ 18

1. Introduction

DONG Energy Burbo Extension (UK) Ltd. (“the Applicant”) has made an application to the Planning

Inspectorate (PINS) for a Development Consent Order (DCO) for the proposed Burbo Bank Extension

offshore wind farm (the Project) located partly within Liverpool Bay / Bae Lerpwl SPA1.

The Applicant has provided an assessment of, amongst other things, the Project's likely effect on the

population of red-throated diver (Gavia stellata), a qualifying feature of the Liverpool Bay / Bae

Lerpwl SPA, as a consequence of permanent displacement from the wind farm site during

construction and operation of the wind farm2. That assessment is documented in the Environmental

Statement3 and Habitats Regulations Assessment Report4 which accompanied the application

documents submitted to the Planning Inspectorate on March 22nd 2013.

Further analysis has been undertaken by the Applicant in response to representations from Natural

England and discussions held with Natural England and Natural Resources Wales. This analysis is

documented in NIRAS (2013), DONG (2013a), and DONG (2014a). This latter Paper ("Red-throated

diver displacement: Clarification of density dependent effects") is used as the basis for this

document to record areas of agreement between DONG Energy and Natural England and Natural

Resources Wales.

A subsequent Paper (DONG, 2014b), submitted by the Applicant for Deadline V, updates this analysis

to calculate displacement effects out to 3 km from the wind farm site. A further update to that Paper

(DONG, 2014c and DONG, 2014d) identifies further evidence to support the Applicant's case that

density dependent effects will not result in an adverse effect on the red-throated diver population of

Liverpool Bay SPA.

2. Red-throated diver

Conservation objectives Red-throated divers are a qualifying feature of the Liverpool Bay / Bae Lerpwl SPA (“Liverpool Bay

SPA”). This SPA was classified in 2010. The SPA conservation objectives for this species are:

• Subject to natural change, maintain or enhance the red-throated diver population

and its supporting habitats in favourable condition.

• The interest feature red-throated diver will be considered to be in favourable

condition only when both of the following two conditions are met:

1 Special Protection Area. 86% of the wind farm area lies within the Liverpool Bay / Bae Lerpwl SPA.

2 It is acknowledge by all parties that red-throated diver as a species are particularly sensitive to displacement

(Garthe and Hüppop (2004), Furness et al.(2013)) 3 Planning Inspectorate document reference 5.1

4 Planning Inspectorate document reference 4.3

o The size of the red-throated diver population is at, or shows only non-

significant fluctuation around the mean population at the time of

designation of the SPA, to account for natural change;

o The extent of supporting habitat within the site is maintained.

The Applicant’s position Natural England / Natural Resources Wales

position

The key potential impact on the red-throated

diver interest feature of the Liverpool Bay SPA

is permanent displacement from the proposed

wind farm area. This could lead to an adverse

effect on the SPA if it led to a significant

reduction in the cited red-throated diver

population of the Liverpool bay SPA due to

emigration or mortality as a result of

permanent displacement from the areas

occupied by offshore wind farms.

The Applicant notes that the Liverpool Bay SPA

covers an area of approximately 1703 square

kilometres. The offshore wind farms

considered in the assessment cover

approximately 7.81% of this area (excluding

any displacement buffer area).

We agree that displacement is the key impact.

Studies of operational offshore wind farms

(OWFs) indicate a consistent avoidance of

constructed OWFs, with little or no evidence of

habituation over time. Such displacement

could cause birds to leave the SPA, or increase

competition for food as birds are obliged to

occupy a smaller area. Mortality from such

‘density-dependent’ competition is a resulting

possibility, although it is not possible to

quantify this directly for red-throated divers.

Including the 3 km buffers of the relevant

OWFs increases the area from which birds are

displaced to approximately 20% of the SPA

habitat covered (though not all divers within

these areas are expected to be displaced). We

also note not all available remaining habitat

within the SPA is likely to be suitable for this

species.

Favourable condition

Although not regarded as threatened within the EU, the conservation status of this species is

regarded as unfavourable because of declines in the European breeding population between 1970-

1990. The population is now considered stable though depleted (Natural England & CCW 2010).

The five year peak mean population at the time of designation was 922 individuals during winter

(2001/02 – 2006/07; insufficient data was recorded for period 2003/2004, JNCC 2010) although

more recent estimates indicate a population of 1,188 (Bradbury et al., 2011).


position

The conservation status of red-throated diver

in Europe is considered to be unfavourable

due to historic declines in the breeding

population.

The species is amber listed in the UK, according

to Birds of Conservation Concern (Eaton et al.

2009). This reflects its ‘depleted’ status as

defined by Species of European Concern

(SPEC)(BirdLife International 2004), within

which it is a SPEC 3 species (unfavourable, not

concentrated in Europe).

The red-throated diver population of Liverpool

Bay SPA is currently in Favourable Condition,

the most recent population estimate indicating

the population exceeds that at the time of

designation.

The SPA was classified in 2010 and is assumed

to be in Favourable Condition. Formally

condition monitoring for the site has not yet

occurred. The most recent survey in 2011 was

designed to test aerial survey methods and

was not part of the monitoring program, which

would normally be expected to capture

variation across time (within and between

winters). However, the value of 1,188 divers

generated, albeit using a new method, was

within the range of variability from past

surveys (e.g. 1,599 in 2001/02; 1,210 in

2002/03).

Data analysis Subsequent to the application it was agreed with Natural England that further analysis of the

potential displacement effects of the proposed wind farm would be undertaken. Natural England

advised (in a meeting on 3/7/13) that the most appropriate data to inform this additional analysis

were an additional data set available from JNCC. These comprised aerial survey data carried out

during winter (October – March) between the winter of 2000/01 and 2009/10, using a line transect

method.


position

The Applicant has used the most appropriate

data available for the analyses of displacement

impacts on the red-throated diver population

of Liverpool Bay SPA.

We agree that the data used are as advised

and represent the best available evidence to

our knowledge.

Interaction Displacement could lead to an impact on Liverpool Bay SPA if it were to cause a loss of birds from

the qualifying population. The birds lost to the population (either through mortality or emigration

from the SPA) comprises that proportion of birds displaced from the wind farm that cannot

redistribute to other parts of the SPA. If the ‘interaction’ of the wind farm with the SPA population is

taken to be the proportion of the SPA population that is lost then this can be expressed as:

Interaction = N * P

Where:

N = Number of birds displaced from the wind farm (expressed as a proportion of the SPA

population as defined in the conservation objectives)

P = proportion birds unable to redistribute within the SPA (this is equivalent to 1 –

proportion successfully redistributing)


position

Calculation of the interaction term (N * P) is

the most appropriate method available for

approximating the likely impact of

displacement on the red-throated diver

population of Liverpool Bay SPA.

We agree this is a useful way to conceptualise

the effect, noting that N is likely to be

evidence-based whereas P may not be.

Magnitude of displacement (N) The value N is estimated using assumptions about the density of divers present and the proportion

of birds within the wind farm and adjacent buffer areas that will be displaced.

Table 1 summarises the values of N for Burbo Bank and other wind farms within Liverpool Bay SPA

(assuming a displacement effect out to 2 km).

Table 1: Cumulative displacement analysis for red-throated diver at four offshore wind farm sites

Offshore Wind farm Year operational Divers displaced % of SPA population

Burbo Bank

2007 11 1.19

Burbo Bank Extension

- 30 3.255

Gwynt y Môr

Expected 2014

(construction started

2012)

35 3.80

Rhyl Flats

2009 24 2.60

Total

100 10.85


position

Table 1 includes those other projects which

could contribute to an in-combination effect

on the red-throated diver population of

Liverpool Bay SPA.

The Applicant understands that the JNCC data

used for the in-combination displacement

analysis were collected between 2000/01 and

2009/10 (See note from JNCC, "Supporting

information for interpretation of density maps"

December 2011). Consequently it is reasonable

to assume that any effect from the Burbo Bank

owf is included in the baseline data.

The Applicant now understands following

advice from Natural England (13/02/2014),

that the JNCC Note referred to here is in error

and that the analysis used data up to February

2007 only. Consequently the Applicant does

not now seek to exclude the Burbo Bank

We agreed at the Issue Specific Hearing that it

was appropriate to exclude North Hoyle OWF,

as the timing of operation coincided with the

beginning of SPA data collection, but not with

the exclusion of Burbo Bank OWF, as operation

did not occur until after the end of the data

collection period. Any putative construction

effects are restricted to the latter end of the

data collection period Assuming construction

began in 2005), and thus the bird distribution

data will be weighted towards pre-construction

years. Therefore it is equivocal that such

effects will have had time to manifest

themselves in the baseline data.

We can confirm that JNCC have indicated their

data for Liverpool Bay were collected up to and

including February 2007 and agree that Burbo

Bank OWF should not be excluded from in

5 Note this figure is lower than the 3.8% potentially displaced by the Project alone as it includes birds displaced

from the zone of overlap with Burbo Bank and its respective buffers.

offshore wind farm from the in-combination

analysis. (The Burbo Bank wind farm was

constructed in 2006 and operational in 2007).

combination tests.

The magnitude of displacement for each wind

farm has been calculated on the basis of the

Kentish Flats Extension (KFE) approach (Model

3) which assumes displacement up to 2km

from the wind farm.

The Applicant has now undertaken

displacement analysis assuming effects out to

3 km. These results are provided in DONG

(2014b).

Natural England / Natural Resources Wales

position

The Applicant has followed the KFE approach,

although Natural England has consistently

advised that it is appropriate to consider

displacement out to 3 km, according to

monitoring data from Kentish Flats OWF.

The likely magnitude (N) of the in combination

effect (including Burbo Bank owf) is estimated

as 10.85% of the SPA population assuming

displacement effects out to 2 km and 11.88%

assuming displacement effects out to 3 km.


position

We agree that these are the magnitude of

effects as calculated in the most recent

clarification note “Red-throated diver

displacement: clarification of density

dependent effects v4a”.

Proportion of birds lost to the SPA (P) It is agreed with Natural England that the proportion of birds lost to the population (P) is < 1 as a

value of 1 would indicate that all birds displaced are lost to the population. It was argued in the

Application for the Burbo Bank Extension that the value of P would be low, because the density of

divers in Liverpool Bay is correspondingly low, when compared to other areas known to support

significant numbers of this species. Consequently, there should be opportunity for many displaced

birds to redistribute.

In addition suitable values for P have also been inferred from density-dependent mortality observed

in oystercatchers (Durell et al., 2000, being the most relevant studies that can be found where this

effect has been quantified empirically, NIRAS 2013). Those studies indicate a density-dependent

mortality rate of between 2.5% - 5%, with 2.5% being the average value indicated by the data and

5% being the most extreme interpretation of the data, including extreme value data points. A

density-dependent mortality rate of 2.5% indicates that for every increase in the density of divers (in

this case assumed to arise when displaced birds redistribute to areas that are already occupied by

some divers) of 1% there will be an increase (of the existing background adult mortality rate) of

2.5%.

These density-dependent mortality rates can be also be expressed (in this case assuming

displacement effects out to 3 km) as a value of P:

Density-dependent mortality of 2% is approximately equivalent to P of 0.31 (or 31%)

Density-dependent mortality of 2.5% is approximately equivalent to P of 0.39 (or 39%)

Density-dependent mortality of 3% is approximately equivalent to a P of 0.46 (or 46%)

Density-dependent mortality of 5% is approximately equivalent to P of 0.77 (or 77%)

A suitable value for P is not known, but is agreed to be less than 1. It is argued that the value for P

should be relatively low because it is considered that there is considerable scope for the

redistribution of divers within other parts of the SPA and other studies (eg. Topping & Petersen

(2011), Kaiser et al. 2005) suggest a low mortality effect for red-throated divers or equivalent

species.

The evidence to support this includes:

The conservation status of this species in Europe is regarded as unfavourable because of

declines in the European breeding population between 1970-1990. Whilst the population is

now considered to be stable it is also considered to be depleted (Natural England & CCW

2010). It is likely, therefore, that the wintering population of red-throated diver has been

higher in the past and that areas, such as Liverpool Bay, would have supported higher

numbers and densities than those currently observed.

The average density of divers within the SPA, in the absence of offshore wind farms, is

calculated to be 0.549 individuals / km2. This is relatively low compared to other areas that

support this species e.g. Thames Estuary, 4 individuals / km2 (Webb et al. 2009).

Once displacement from the proposed Burbo Bank Extension and other relevant offshore

wind farms is taken into account, this density increases to 0.616 individuals / km2 (2 km

displacement) and 0.621 individuals / km2 (3 km displacement) This is a relatively small

change (~12%). Shown graphically (Figure 1) it can be seen that the resulting densities are

well within the range of those observed in Liverpool Bay.

Kaiser et al. (2005) modelled the likely effect of displacement arising from expected wind

farm development on common scoter in Liverpool Bay. Common scoter are considered to

share the same sensitivity to disturbance and habitat specialism (although not the same prey

species) as red-throated diver (Furness et al., 2013) and therefore may be considered a

suitable proxy for an analysis of the consequences of displacement in Liverpool Bay SPA. The

aim of the model was to predict the consequences of displacement expressed as changes in

the overall mortality rate of common scoter in Liverpool Bay. The model incorporated

information about the distribution and variability in prey availability and correlated these

with observed patterns of common scoter distribution. Information on the energetics

associated with foraging by common scoter was also included to explore the effects of

displacing them from the wind farm area. The distribution of the prey of common scoter

(bivalves) are patchily distributed leading to distinct aggregations of common scoter within

Liverpool Bay. The model identifies that the displacement of common scoter from wind

farms at Rhyl Flats, Burbo Bank, North Hoyle and Gwynt y Mor is not predicted to have any

significant adverse effects on common scoter mortality. Only when the proposed (at that

time, but not subsequently delivered) wind farm at Shell Flats is included is a significant

effect on mortality predicted (increasing from a median value across Liverpool Bay of 7.3%

to a median value of 11.7%, an increase of 60% in the overall winter mortality rate)

reflecting the value of the Shell Flats area to over wintering common scoter. It is assumed

that the consequences of displacement for common scoter are greater than they are for red-

throated diver which are much more widely dispersed within Liverpool Bay and which do not

show the same degree of aggregations, presumably because their prey is similarly dispersed

and disaggregated.

Topping & Petersen (2011) developed an Agent-based model to assess the population-level

consequences of displacement of red-throated divers by offshore wind farms in the Baltic

Sea and Danish waters. They modelled various scenarios, but the scenario which assumed

most wind farm development (all existing and proposed offshore wind farms in the Baltic

Sea and Danish waters) predicted a 1.7% reduction in red-throated diver numbers in the

flyway. Although the authors make many assumptions which consequently does not allow a

direct comparison with red-throated diver in Liverpool Bay SPA, the results point to a very

small population impact arising from a relatively large extent of development (15,000km2 of

wind farms).

Figure 1. Distribution of estimated density of red-throated diver in Liverpool Bay SPA6

6 Figure 1 presents the frequency distribution of estimated density of red throated diver for all 1 km x 1 km

grid squares within Liverpool Bay SPA. This dataset had been derived from JNCC data on the number and distribution of red-throated divers in Liverpool Bay SPA as determined using visual aerial survey methods which have been corrected for distance related detection errors. Bird observations were smoothed by JNCC using kernel density estimation (KDE) and were combined to create a mean modelled density surface of red-throated diver in Liverpool Bay SPA (NIRAS 2013).

Arrows and red columns identify the mean estimated density of birds in the SPA, outside of wind farms and buffers: (1) before displacement, (2) after displacement (2km buffer) (3) after displacement (3km buffer)


position

It is agreed that P<1 We agree that it is very unlikely that all of the

birds displaced will die, and thus agree that P

<1.

There are few empirical studies to inform likely

density-dependent mortality relationships. The

studies on oystercatchers are the most

relevant information that is available.

However, the Applicant notes that the

assumption of a 5% density dependent

mortality effect for red-throated diver in

Liverpool Bay SPA is highly pre-cautionary due

to the overall low density of divers in this SPA

and evidence for recent diver populations in

the SPA in excess of the citation value. The

Applicant argues that the calculated increase in

overall density is not sufficient to increase

diver mortality (or loss) to an extent which

would adversely affect the integrity of the SPA.

The Applicant additionally makes reference to

the study modelling predicted common scoter

mortality in Liverpool Bay (Kaiser et al. (2005))

and the modelling of red-throated divers off

the Danish coast (Topping and Petersen,

(2011)) to support its contention that a 5%

density-dependent effect is highly

precautionary.


position

There are few studies to inform likely density-

dependent mortality relationships. The

oystercatcher is one of the few species in

which the density-dependence of

overwintering mortality has been quantified.

Oystercatchers’ foraging ecology makes them

particularly prone to strong density-dependent

competition for access to their food resources.

While clearly oystercatchers and red-throated

divers cannot be considered similar in terms of

their ecology, application of the oystercatcher

density-dependent mortality function to help

inform assessment of the significance of

predicted impacts of red-throated diver

displacement (and resultant increase of density

and hence mortality) provides a reasonably

precautionary basis on which to make that

assessment given the apparent severity of the

density-dependence inferred from this other

species.

Using the increase in density resulting from

displacement is probably a more useful

measure than referring to absolute densities,

as we do not know whether the current

Liverpool Bay SPA red-throated diver density is

limited (or limiting further increases).

Whilst the Kaiser et al. (2005) modelling

predicted a median increase of 60% in over

wintering mortality of common scoter, these

data can also be interpreted as a worst case of

121% additional mortality when expressed as

an increase from baseline mortality.

We consider that there are several reasons to

have a low confidence in the application of the

modelling by Topping & Petersen (2011) to the

Liverpool Bay SPA situation, largely based on

the assumptions made and which the Applicant

partially acknowledges. For instance: the study

assumes a 500 m displacement buffer (not a

variable 3 km buffer as we would advise); the

density-dependent relationship is not

obviously defined (i.e. we can’t tell what P is);

the spatial scales are not comparable (i.e. we

don’t know if the % of habitat lost is

comparable with Liverpool Bay); the starting

population is ‘arbitrary’, not measured; and

changes are not expressed in terms of

increases to baseline mortality and thus we

cannot estimate P. There are several other

assumptions and caveats which the authors

themselves highlight.

The data on oystercatchers indicates that

density-dependent mortality is likely to be no

greater than 5% and probably lower (between

2-3%)

The Applicant agrees that in this case the

relationship between displacement and

mortality (loss) will be weaker and understands

that a "P" value between 0.30 and 0.45 is more

appropriate for this analysis and was the more

usual value reported in the Durell study (Durell

et al., 2000).


position

The data on mussel feeding adult

oystercatchers indicates that the density-

dependence of over-winter mortality is such

that a doubling of density results in up to a

five-fold increase in baseline mortality but that

the relationship may be less strong than this

(i.e. between a 2 – 3 fold increase).

We do not agree that the lower P values are

‘more appropriate’ but recognise the situation

has some uncertainty.

Density-dependent mortality of 5% is

approximately equivalent to P = 0.75 for a

displacement effect out to 2 km, and P = 0.77


position

for displacement out to 3 km. Application of this strong density-dependent

mortality function to the Liverpool Bay SPA

red-throated diver data, and in particular to

the number of birds predicted to be displaced

and the density of birds in the remaining areas

to which displaced birds might relocate,

indicated a 12% increase in density might occur

in those areas and the predicted additional

mortality of a number of birds equivalent to

75% of the number predicted to be displaced

(P=0.75)out to 2 km, and 77% (P=0.77) out to 3

km.

There is evidence to suggest that it is unlikely

that P > 0.75 but likely that P < 0.75

The Applicant interprets the evidence from the

study on the Exe estuary to support the

contention that it is unlikely that there is a

strong density-dependent function relationship

in the Liverpool Bay SPA red-throated diver

population; and, on the contrary, the low

densities and variable population numbers

within the SPA suggest there is likely to be a

weak relationship between displacement and

loss to the SPA at this site. Data from

oystercatchers indicates that a P in the range

0.30 – 0.45 is more likely.


position

Given that the value of P=0.75 is derived on

the basis of what is likely to be a strong

density-dependent function to the Liverpool

Bay SPA data , it is relatively unlikely that P

would be any greater than 0.75 in the case of

red-throated diver. This appears to be a

suitably evidence-based but precautionary

assumption in this instance. Note though that

application of the same density-dependent

mortality function to other instances of diver

displacement may result in P>0.75 if the

number of displaced birds is greater than that

considered here and in particular if the %

increase in density that results in the remaining

areas due to displacement of birds into them is

also greater than that calculated to occur in

this instance.

Figure 2 indicates, graphically, how the magnitude of displacement (N) relates to interaction

depending on the assumed value of P. The consented mortality (interaction) rates consented in

recent applications in the Thames Estuary are indicated (Kentish Flats Extension in 2013 at 9.3% and

Gunfleet Sands in 2008 at 6.5%). The purple rectangle indicates the value that would need to be

assumed for P if the interaction value for Burbo Bank Extension was to be within the range of

previous consented rates.

It can be seen that value of P would have to be very high (~0.75), which equates to the most

pessimistic interpretations of the density-dependent mortality data. The evidence for oystercatchers

indicates that a density-dependent mortality rate between 2% to 3% is more likely, equivalent to

values of P that lie between 0.3 – 0.45, implying an interaction rate that is considerably lower than

that already consented elsewhere.

Figure 2: Interaction rates


position

It is agreed that for a value P ≈ 0.75 the

interaction figure for Burbo Bank Extension

would be approximately 8.14% (10.85%

multiplied by 0.75).

The analysis of displacement out to 3 km, using

the suggested 20% displacement rate between

2km and 3km, identifies a total of 110 birds

displaced (including from Burbo Bank owf).

This is equivalent to 11.88% of the SPA citation

population (922 birds). The "P" value, based on

a worse case density dependent mortality, is

0.77 giving an interaction value of 9.15%.

Mathematically, we agree, noting the value of

N is based on a 2 km buffer which we advise

may underestimate the effect of displacement.

It is agreed that these values would be in a

similar range to those already consented in the

Thames Estuary (between 6.5% at Gunfleet

Sands to 9.3% at Kentish Flats Extension).


position

Mathematically, we agree, noting that Natural

England did not agree to all of the elements of

the assessment for KFE (notably the exclusion

of certain wind farms from assessment and the

appropriate displacement buffers), nor did we

advise that adverse effect on site integrity

could be excluded beyond reasonable scientific

doubt.

Slightly lower (but still credible) values of P

would result in interaction figures that are less

than those already consented in the Thames

Estuary.

Using the 2 km displacement scenario and

values of P = 0.3 and P = 0.45 the interaction

values are:

10.85% x 0.3 = 3.26%

10.85% x 0.45 = 4.88%

Using the 3 km displacement scenario and

values of P = 0.31 and P = 0.46 the interaction

values are:

11.88% x 0.31 = 3.68%

11.88% x 0.46 = 5.47%


position

Mathematically, we agree.

It is likely, in any case, that the value of P <

0.75 because:

the density of divers in Liverpool Bay is

low, when compared to other areas known

to support significant numbers of this

species

the change in density of divers in receptor

areas arising from the displacement of

divers from the wind farm area is relatively

low

A value of P = 0.75 based on the

oystercatcher study (Durell et al., 2000)


position

We advise that there is insufficient

understanding of the system to conclude that P

< 0.75 beyond reasonable scientific doubt.

Although diver density is lower than in the

Outer Thames Estuary, we do not know

whether the system in Liverpool Bay is at

carrying capacity. Similarly, the latest

assessment of density changes within Liverpool

Bay SPA following displacement (i.e. from an

average of 0.549 to 0.616 divers per km2)

refers to a scenario where all remaining

uses the extreme value of mortality from

deaths observed in the 1990/91 winter.

habitat, regardless of quality, is available to

red-throated divers. We do not know whether

this is the reality. Finally, P = 0.75 is based on

empirical data from oystercatchers and

represents a scientifically derived value.

We do not know whether red-throated divers

respond to the same environmental variables

as oystercatchers (for example, sea state may

be more important than air temperature), nor

whether future winters will be more like that

of 1990/91 than any other winter.

Conclusions


position

The Applicant has made use of the best

available evidence to assess the likely effects of

the proposed Burbo Bank Extension on

Liverpool Bay SPA.

It is the Applicant’s position that the density-

dependent mortality relationship for red-

throated diver at this SPA is unlikely to show

the worst case strong relationship suggested in

the study of mussel-feeding oystercatcher on

the Exe estuary (Durell et al., 2000). That study

showed that an approximate doubling of the

density of oystercatchers feeding on mussel

beds in the Exe estuary resulted in an

approximate tripling of the winter mortality

rate for those birds, a density dependent

mortality effect not shown for oystercatcher

feeding in other (more extensive) habitats on

the estuary. The 1:5 density dependent

mortality relationship (ie. 1% increase in

density leading to a 5% increase in mortality

rate) only occurs if the extreme mortality

values from the severe weather winter of

1990/91 are used. The Applicant notes that the

physically constrained mussel-bed food

resource and the high bird densities (up to 30

We agree the JNCC data used for in

combination are the best available data. We

acknowledge the use of oystercatcher density-

dependent data although we cannot test its

applicability to red-throated divers, especially

as we do not understand the extent to which

fish prey, and access to fish prey, are spatially

or temporally constrained ; however,

oystercatchers are expected show a

comparatively strong density-dependent

relationship. We continue to disagree over

interpretations of evidence on the appropriate

displacement buffers, though the Applicant has

now presented the outcomes from both

potential scenarios.

birds per hectare) in that study are not

replicated for fish-eating red-throated diver in

Liverpool Bay SPA.

There is no indication that the proposed

development alone will adversely affect the

favourable condition of the SPA through a

reduction in the size of the red-throated diver

population.

The predicted level of displacement from the

Project alone (3.25% of the SPA population

assuming effects out to 2km and 3.56%

assuming effects out to 3 km) is substantially

less than that consented at other wind farms,

and this is the case regardless of the assumed

value of P.


position

We have agreed the project alone is unlikely to

result in an adverse effect on site integrity.

There is no indication that the proposed

development in combination will adversely

affect the favourable condition of the SPA

through a reduction in the size of the red-

throated diver population.

Considering the extent of the habitat available

at this SPA and the relatively low densities of

red-throated diver observed at the site the

Applicant’s position is that P = 0.75 is too

precautionary and that the evidence points to

a value that is significantly lower than this. The

implication otherwise is that 3 out of 4 birds

displaced (that is, potentially unable to make

use of the wind farm area and displacement

buffer) subsequently die (or are lost to the

SPA) as a result and this is not a credible

scenario given the extent of available

alternative habitat and the relatively low

densities within those area. Notwithstanding

this point, however, even if a value of P=0.75 is

adopted (at either 2km or 3km displacement

scenarios) the resulting impact is, in every

case, within the scale of effect for this species

that has already been consented elsewhere.


position

We advise that it is not possible to rule out an

adverse effect on site integrity beyond

reasonable scientific doubt. This is because of

different interpretation of the evidence

informing appropriate displacement buffers,

and because of the uncertainties surrounding

the mortality (P) resulting from displacement.

We note that even at P = 0.75, 1 in 12 divers

are predicted to suffer mortality.

References

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Liverpool Bay Special Protection Area. HiDef Aerial Surveying Limited and Wildfowl & Wetlands Trust

(Consulting) Ltd.

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BURBO BANK EXTENSION OFFSHORE WIND FARM ... 1 Burbo Bank Extension offshore wind farm Supplementary...

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