Aarhus University Seal / Aarhus Universitets segl

No. 42: Effects on harbour porpoises from Rødsand 2 Off-shore Wind Farm

Teilmann, J., Tougaard, J. & Carstensen, J. 2012. Effects on harbour porpoises from Rødsand 2 Off-shore Wind Farm. Aarhus University, DCE – Danish Centre for Environment and Energy, 66 pp. Scientific Report from DCE – Danish Centre for Environment and Energy No. 42 http://www.dmu.dk/Pub/SR42.pdf

 

Summary

E.ON Vind Sverige has been commissioned the construction of Rødsand 2 Offshore Wind Farm comprising 90 wind turbines, south of Lolland-Falster, Denmark. The location of the wind farm is west of and adjacent to the existing Nysted Offshore Wind Farm with 72 turbines. The two wind farms are spaced about 3 km and in combination represents the largest wind farm area in the world.

This report investigates the potential effects of the Rødsand 2 Offshore Wind Farm as well as the cumulative effect of both wind farms on harbour porpoises. Porpoises were monitored by automatic acoustic dataloggers (T-PODs) according to a BACI design and deployed during a baseline period from 24 September 2008 to 16 February 2009 and during normal operation from 24 September 2011 to 2 March 2012. These instruments were deployed at 10 stations covering a coastal stretch of 35 km from Gedser to Rødby, including the wind farm area with reference areas on both sides that are assumed to represent the same type of habitat to the porpoises. Instruments were not moved between stations during the study to reduce variation from inter-instrument variation in sensitivity. In addition, background noise at four of the T-POD stations was recorded by automatic noise loggers during 45 days and 49 days during the two monitoring periods, respectively.

In order to assess the potential cumulative effect of two adjacent wind farms, the data from the monitoring program of harbour porpoises at Nysted Offshore Wind Farm were analysed together with the more recent data from the Rødsand 2 Offshore Wind Farm.

The total monitoring period covered 1824 days for all recording instruments in total, almost equally distributed between baseline and operation. Four indicators of harbour porpoise echolocation click activity was extracted, in line with previous studies at other offshore wind farms. These are 1) Click intensity (Clicks/PPM), indicating as the daily average number of clicks produced per minute for minutes where porpoises were recorded, 2) Porpoise positive minutes (PPM), indicating the percentage of minutes per day where clicks were recorded, 3) Encounter duration indicating the duration of porpoise acoustic encounters (defined as separated from pervious encounter by at least 10 minutes of silence), 4) Waiting time, indicating the time between two porpoise acoustic encounters.

Underwater noise in the area showed a pronounced peak in the frequency spectrum around 1000 Hz consistently across all stations. This signal is considered to originate from the deep water shipping lane south of the measuring stations. Systematic differences among stations included a generally lower noise level in the existing wind farm and highest noise level at the easternmost station, which was located close to the sailing route into Gedser harbour. Underwater noise was generally higher during the baseline period in 2008/2009 for all areas, than during the operation period in 20011/2012 probably due to more rough weather conditions in the baseline period. However, the Rødsand 2 area was particularly noisy during the baseline period. This is also partly supported by the number of ships related to the wind farm present in the wind farm area during the baseline period, where exploration and other activities were already started. It is therefore a possibility that the porpoises in the Rødsand 2 area were already affected by noise from ship activity during the baseline period.

We found no overall change in echolocation activity over the entire monitoring area from baseline to operation of Rødsand 2 Offshore Wind Farm. Also, there was no significant change in the echolocation activity in Rødsand 2 Offshore Wind Farm relative to each or a combination of the three reference areas, i.e. changes from baseline to operation were similar in the impact and reference areas. Also no significant change in noise levels audible to porpoises was found. This could be due to a generally high noise level in the area, masking the turbine noise or that the noise loggers in the wind farm were deployed between the wind turbines, i.e. at distances ~350-450 m from the turbines.

This study also shows that the echolocation activity has declined in Nysted Offshore Wind Farm since the baseline in 2001-2002, which is consistent with earlier reports, and has not fully recovered yet. However, when comparing the wind farm area with the reference area in the most recent monitoring period (2011-2012, operation period 4), there was a relatively higher echolocation activity than during the construction period (2002-2003) and operation period 1-3 (2004-2006 and 2008-2009), showing a significant increase from construction to operation period 4 in click PPM and encounter duration as well as significant increases in PPM from operation periods 2 and 3 to operation period 4. This suggests that the strong negative effect on porpoises in Nysted Offshore Wind Farm is gradually diminishing possibly due to a habituation of the porpoises to the wind farm.

We found no cumulative effect of the two wind farms together. The gradual return of porpoises in Nysted Offshore Wind Farm seemed to be unrelated to the construction of Rødsand 2 Offshore Wind Farm. A similar effect on the porpoises at Rødsand 2 Offshore Wind Farm as found for Nysted Offshore Wind Farm could be expected. We have no good explanation for the lacking effect and can only speculate that the elevated noise or changes to the prey availability during the baseline period could have an effect on our results or that there was an already low porpoise presence in the Rødsand 2 area caused by a potential barrier effect by Nysted Offshore Wind Farm, when the animals move along the coast in an east-west direction. This is the first time the effect of two wind farms next to each other have been studied and the potential explanations to the observed differences are pure speculation.

A potential positive effect of the wind farms over time, as organisms grow on the foundations and increase forage possibilities, have not been studied. To fully understand the long term effect of wind farms a continuous monitoring program with detailed information on the behavior of porpoises inside and around wind farms is required.