Assessment of the Effects of the Offshore Wind Farm Egmond aan Zee (OWEZ) for Harbour PorpoisePurpose:"The aim of this study was to investigate whether the Offshore Wind farm Egmond aan Zee(OWEZ) has influenced the occurrence of harbour porpoises.In order to evaluate the environmental impacts of OWEZ, porpoise acoustic activity in thearea was monitored;1) during a baseline (T0) study 2003/2004 (Brasseur at al. 2004)2) after the construction of the wind farm (T1) from 2007 to 2009.The comparison between the T0 and the T1 was conducted to determine if and how harbour porpoise occurrence is affected by the presence of the wind farm. Harbour porpoise activity and presence was measured by acoustic monitoring of echolocationsounds at eight stations equipped with stationary acoustic porpoise detectors (T-PODs) whichwere permanently deployed and were operating on a 24 hour basis. During both the T0 and T1study the T-PODs functioned very well and provided a wealth ofdata. Four indicators of click activity (porpoise positive minutes, clicks per porpoise positive minutes, encounter duration and waiting time between encounters) were chosen for the analyses. These indicators can be related directly to porpoise occurrence and habitat use in the study area. To investigate a potential effect of the wind farm a statistical Before-After Control-Impact (BACI) design was used. Here conditions in the wind farm (impact area, T1) were compared to both the baseline conditions (T0) and to conditions in the nearby reference area.The acoustic results show a strong seasonal variation in harbour porpoise occurrence, with more recordings of animals in the autumn/winter/spring seasons compared to the summer months. This pattern was similar in both the T0 and in the T1 study.There was a general increase in harbour porpoise occurrence from T0 to T1 for all T-POD stations, which was confirmed by an increase in porpoise sightings in the Dutch coastal area. During T0, the spatial distribution of porpoises did not differ significantly between the impact area (wind farm) and the two reference areas north and south of the wind farm.The results of the BACI design showed that during the T1 porpoises showed a significant change in distribution between the reference areas and the impact area. A higher porpoise acoustic activity was recorded inside the wind farm relative to outside, which is most likely linked to an increase in local porpoise occurrence. Because of the introduction of new T-PODs to the study and the specific differences between individual T-PODs , the variation between these devices might have caused a higher variation in the resulting data. Thus, when interpreting the effects, one should take into account that the confidence interval of the results might be larger and that the true effect might be stronger or lower than the one reported here. However, this does not influence the overall conclusions.The cause behind the increase of porpoises in the farm could not be determined, but may be linked to increased food availability due to the reef effect of the turbine foundations and the exclusion of fishery from the wind farm. The increase of harbour porpoise acoustic activity inside the wind farm is in contrast to results from other offshore wind farms. This shows that results from one wind farm are not necessarily transferable or valid for other wind farms located in different areas."

Field survey on juvenile bivalve densities October 2007Measurements made of density of chlorophyll, the velocity of the current and temperature.vessel: RV POSEIDON (IFM Geomar, Germany)sampling stations: 20 stations in OWEZ and 10 stations in each of the 5 reference areas R2, R3, R4, R5, RL (for geographic positions of stations see worksheet geographical positions stations)sampling design: 1 boxcore per stationsampling gear: NIOZ boxcorer, sampling depth 20 cm, sampling diameter 30 cmsample surface juvenile bivalves: 0.024 m2 (i.e. 3 sub-cores each with diameter 10 cm2 per boxcore)sample depth juvenile bivalves: 5 cmsorting procedure lab: stacked sieves 1.0, 0.5 and 0.2 mmfollowing worksheets describe: *number of identified juvenile bivalve species (> 0.5 mm) found per boxcore (0.024m2) and per m2Station,Date time,species,n bivalves > 0.5 mm per 0.024m2,n bivalves > 0.5 mm per m2