Effects from the Construction of Nysted Offshore Wind Farm on Seals in Rødsand Seal Sanctuary Based on Remote Video Monitoring


Title: Effects from the Construction of Nysted Offshore Wind Farm on Seals in Rødsand Seal Sanctuary Based on Remote Video Monitoring
Publication Date:
June 01, 2004
Pages: 33
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Edrén, S.; Teilmann, J.; Dietz, R.; Carstensen, J. (2004). Effects from the Construction of Nysted Offshore Wind Farm on Seals in Rødsand Seal Sanctuary Based on Remote Video Monitoring. Report by National Environmental Research Institute (NERI). pp 33.

This report describes the effect of the construction of Nysted Wind Farm on the seals hauling out in Rødsand seal sanctuary. A remote-controlled webbased camera system was used to monitor the seals in daylight hours. The camera systems, powered by solar and wind energy are designed to operate under extreme weather conditions. Live images are transmitted to a land station, from where it is streamed to the Internet. The cameras are operated remotely and pictures are stored every 5 seconds. Two cameras were mounted on a 6 m high tower in Rødsand seal sanctuary. The tower is placed about 300 m from the seals preferred haul-out site without any notable effect on the seals.


The seasonal variations in the presence of seals in the Rødsand sanctuary were clearly distinctive with a generally low presence during winter months increasing in spring and reaching its maximum in August when seals were almost permanently present at the sand bank. The diurnal variation showed the highest presence during the middle of the day.


The distinct seasonal and diurnal patterns of seal occurrence were confirmed by the marginal category probabilities derived from a multinomial model. The diurnal variation corresponded to a overall mean of 6.3 seals around noon decreasing to less than 1 in the early morning and late evening by translating the categories into mean number of seal as above.


Southerly winds around 4-8 m/s increased the number of seals on land. If the wind came from the south (S) there would be a yearly mean of 5.0 seals on land, whereas if the wind was from the north (N) there would only be a yearly mean of 1.5 seals on land. The yearly mean number of seals on land increased from 2.0 seals at 0 m/s, reaching a maximum of 3.4 seals at 6.1 m/s and decreased to 0.2 seals at 20 m/s. Wind speed between 0 and 12 m/s generally resulted in high abundance, whereas strong winds did not favour seals on land.


There was no change in the disturbance rate during the construction period, probably due to a regulation on boats to pass the sanctuary in adequate distance. This indicates that remote boat traffic and other activities that the seals have experienced previously, although intensified during construction did not affect the number of seals on land.


The number of seals on land increased 12.5% from a yearly mean of 2.79 seals in the baseline period to 3.14 seals in the construction period. Five months had seals observations in both the baseline and the construction period, and four of these had a significant difference in the category probabilities for the two periods. There was a decline in the number of seals on land from April 2002 to April 2003, whereas data from May, June and July all showed increases from 2002 to 2003. August was not significant.


There was, however, a significant decrease in the number of seal on land during the ramming periods, that was carried out during at a single foundation located approximately 10 km SW of the seal sanctuary. The observed reduction of seals varied among months ranging from 8 to 100%. When correcting for other variables in the model the reductions varied between 31 and 61%. The seals may have chosen to stay in the water, swim away or haul out further away from the wind farm than Rødsand.


The construction work on the wind farm situated approximately 4 km away from the Rødsand seal sanctuary had in general no or little effect on the presence of seals. Even two grey seal pups were recorded during the construction period.


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