East Anglia ONE Offshore Windfarm


April, 2016


gannet, simulations were only conducted for this species. As this was also the least abundant species this also ensured the results would be precautionary.


14.


A permutation test was used to provide a measure of the probability of obtaining the density estimated within the buffers from the actual wind farm location compared with those for the re-sampled wind farm locations.


3 Results 3.1 Spatial Modelling 15.


The results of initial analyses to detect post-construction displacement of gannet, kittiwake and guillemot are provided in Table 2. Parameters which were modified in the simulations were:


 Magnitude of displacement of individuals from the wind farm (30% or 50%);  Transect spacing (1.4km or 2.2km); and,  Survey frequency (1 or 2 surveys per month).


Table 2. Initial power analysis results. Scenarios with power >0.8 (i.e. >80% detection of effect) are highlighted in underlined bold.


Species Gannet


Percentage displaced


30 30


Kittiwake Guillemot 16.


50 50 30 30 50 30 30 50 30


50


Transect spacing


2.2 1.4


2.2 1.4 2.2 1.4 1.4 2.2 1.4 2.2 2.2


2.2 Area surveyed (%) No. surveys / month Power


11.7 17.3


11.7 17.3 11.7 17.3 17.3 11.7 17.3 11.7 11.7


17.3


1 1


1 1 2 2 2 1 1 1 1


1


0.58 0.5


0.62 0.65 0.54 0.58 0.83 0.46 0.46 0.85 0.84


0.94


Guillemot displacement was identified with a high power with a small effect size (30%), widely spaced transects (2.2km) and a single survey per month. This reflects the relatively high densities recorded during the baseline surveys. Kittiwake displacement was identified under similar conditions, although only if a larger percentage (50%) were displaced. In contrast, gannet required more survey effort (2 surveys per month), closely spaced transects (1.4km) and a large effect size (50%) in order to achieve a power of 80%.


17.


From the results obtained it can be seen that the power to detect a displacement effect was influenced by two factors: the magnitude of effect (i.e. percentage displaced) and the sample size (i.e. number of birds recorded in transects), which was a function of seabird density, transect spacing and number of surveys per month. Comparing the individual results, it appears that the biggest influence on power was the magnitude of displacement. For example, the power to detect a displacement rate of 30% for kittiwake remained low even when survey effort was increased by 50% (2.2km spacing to 1.4km spacing), but if 50% were displaced the power almost doubled. A similar pattern was seen with gannet, although in this case the effect was only observed when the survey frequency was doubled to two per month. This is likely to reflect the fact that gannets were only recorded in five months between October and April.


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