bok%3A978-3-658-02462-8.pdf?auth66=1398409209_a0514c2b8e531c058ab8b810a0cad74d&ext=

144Chapter 13 • Effects of alpha ventus on harbour porpoises1234567891011121314151617181920..Fig. 13.8 Estimated density of harbour porpoises in the study area. Error bars show 95 % confidence limits. Surveys conductedduring pile driving or within 48 hours following pile driving at alpha ventus are underlined in red.converter platform, installed in 2009, may have hadan impact on the results.13.3.3 Effects from the wind turbinesduring operationModelling was conducted using GAMLSS (Rigby &Stasinopoulos 2005) – a library for the open sourcestatistics software R (R Development Core Team2012). The data for 2011 (dph from click detectorsdeployed in the same design as for the constructionperiod) was split and one model was constructed usinga ‘zero inflated binomial’ distribution with datafrom periods when the turbines were switched off.The dph (transformed for presence/absence only)were used as the dependent variable, and the independentvariables were distance to the windfarm,wind speed and the number of registered clicks (infour classes from 0 to 50,000 clicks/h; data weretruncated at 50,000 clicks/h before analysis). Datawas sparse for times when wind turbines wereswitched off. Hence, a random sample was selectedfrom the data set for operational wind turbines toprovide the same sample size as for the ‘off ’ situation.The resulting dataset is small (310 samples) andhence the analysis shows wide confidence limits(. Fig. 13.9). Especially for effects close to the windfarm,the analysis does not show a clear result dueto large modelled variation.It must, however, be noted that the closestC‐POD position was deployed at 0.5 km from thenearest turbine. It is unlikely that an artificial reefeffect or a noise effect would have significant impacton the registration rates at that station. The analysishence shows that while very close range effects mayoccur, they most probably do not have a larger scaleeffect on porpoise detection rates.13.4 DiscussionDuring the course of the study at the alpha ventustest site, more results became available from otherwindfarms, as did additional results from alpha ventusby means of the StUK3 monitoring programme.The StUK3 results indicate, similarly to the findings