Abstract
Over the period October 2003 to August 2004 E.ON UK Renewables Offshore Wind Limited constructed a 60 MW wind farm comprised of 30 x 2 MW turbines on Scroby Sands, a dynamic sand bar system approximately 2 km offshore from North Denes, Great Yarmouth, Norfolk. The development is located about 2 km north of an area used by Harbour seals Phoca vitulina as a breeding and haul-out site for at least a century, and more recently (from 1958) by Grey seals Haliochoerus grypus for hauling out. The former small breeding colony of the latter on Scroby Sands was abandoned following the covering of the bank at high tide from 1966 onwards. Breeding now takes place on a mainland beach some 20 km away to the north near Horsey Gap.
The Schedule to Licence required that a monitoring programme be carried out to determine the impact of the wind farm on the seal populations. This was specified as two aerial photographic surveys from fixed wing aircraft per month at low water for the six summer months (April to September) pre, during and post construction. Baseline pre-construction data was gathered in 2002 and 2003, construction data was gathered in 2004, and postconstruction data was gathered in 2005 with the addition of 2006 following significant change in local seal populations. Further recommended modifications to the survey programme included further surveys to assess Harbour seal pup production during summer and winter surveys to assess the use of the Sands by Grey seals in particular in this period.
In total, 64 surveys were carried out during the study period from March 2002 to October 2006, exceeding the FEPA licence requirements. However, it should be highlighted that monitoring was only a specified requirement from April-September, which meant that no surveys were undertaken during the period of pile driving from October 21st 2003 to January 1st 2004, known to be the most disturbing element of the construction process for seals from studies conducted at other offshore wind farms (OWF’s) in Sweden and Denmark. In summary, it has been calculated that the noise of pile-driving may be detected by seals at beyond 80 km from the source, with the potential for some form of response through disturbance of up to 20 km and the prospect of hearing damage at up to 400 m. Severe injuries (most likely resulting in death) cannot be ruled out in the immediate vicinity of pile-driving.