Thursday, December 07, 2006

Danish Study of Offshore Wind Farms Finds Limited Impacts on Birds, Fish, and Mammals

The Danish government has published the results of an eight-year study of the impacts of offshore wind farms on the aquatic ecosystem. The study evaluated the impacts of the world's two largest offshore wind farms, Horns Rev and Nysted, on birds, fish, and mammals, among other things.

The Report, “Danish Offshore Wind – Key Environmental Issues” (large PDF) was released to the public during a conference at the end of November. It was prepared by the Danish Energy Authority, Danish Forest and Nature Agency, and the two companies that own the offshore wind farms (Dong Energy and Vattenfall wind).

The report includes some key findings on the two projects' impacts on birds, fish, and mammals and contains commentary from the International Advisory Panel of Experts on Marine Ecology, which gave the report a positive evaluation.
  • Birds:
“The Thermal Animal Detection System (TADS) provides empirical evidence that waterbird collisions are rare events. Collision risk modelling and bird tracking by radar as well as visual observations show that many waterbirds species tend to avoid the wind farm, changing flight direction some kilometers away to deflect their path around the site. Birds flying through the wind farm tend to alter altitude to avoid the risk of collision. Under adverse weather conditions, which were thought to be likely to increase collision risk, results show that waterbirds tend to avoid flying”.

“Radar studies at Horns Rev and Nysted also confirm that may birds entering the wind farms re-orientate to fly down between turbine rows, frequently equidistant between turbines, further minimizing collision risk.”

“Avian avoidance behavior of turbines minimized collision risk, and these early post-construction studies show that, despite very heavy common eider migration in the Nysted area, their avoidance of turbines at different spatial scales resulted in very low modelled collision risk…amounting at Nysted (with 95% confidence) to 40-50 common eiders on average per year, less than 0.05% of the annual hunt in Denmark (currently approx 70,000 birds).”

“The Danish research has developed valuable new tools for study of birds in relation to marine wind farms, and has provided insights into the flexibility of waterbird behavioural responses to the hazard of turbines suggestion that collision rates are likely to be less of a problem than often suggested.”

(note: both Horns Rev and Nysted located in close proximity to European Union Special Protection Areas which were established as a result of the abundance of birds in the area).
  • Fish:
“At both wind farm sites, fish were often found swimming around the artificial reef structures apparently searching for food and shelter”.

Yet fish populations at the wind farms appear to be similar to what they were before the construction of the wind farms.

“A likely explanation is that the hard substrate habitats at Horns Rev were still young and biologically immature at the time of surveying. Therefore, the reef effect at Horns Rev may become more pronounced in the coming years as colonisation and development of the biological communities progress. At Nysted, the effect was weak presumably because the benthic community consisted of a monoculture of large common mussels that are only moderately attractive to most fish species.”

“Investigations into the effects on fish and fish behaviour from electromagnetic fields were made at Nysted. Data have documented some effects from the cable route on fish behaviour indicating avoidance of the cable as well as attraction, depending on the species.”
  • Mammals
“The close vicinity [4 kilometers] of the Rødsand seal sanctuary to the [Nysted] wind farm and the fact that Rødsand is the only known breeding site for the grey seal in Denmark made Nysted a key site for the study of seals on land.”

“Five harbour seals and six grey seals were captured in the Rødsand seal sanctuary and a satellite tag was glued to the fur on top of the head. The tags stayed on until the seals moulted their fur during the following summer. Daily locations showed that the harbour seals remained within 50 km of the tagging site year-round, while the grey seals made extensive movements up to 850 km away from Rødsand to Sweden, Germany and Estonia.”

“Both wind farm areas were found to be part of much larger foraging areas used by the seals. No general change in behaviour at sea or on land could be linked to the construction or operation of the wind farms. The only effect detected on land was a reduction in the number of seals on land during pile driving operations at Nysted.”

“To protect seals and porpoises from exposure to the excessive noise levels close to the foundations, the pile driving force was slowly intensified (ramped up) and underwater acoustic alarms (porpoise pingers and seal scarers) were deployed at both Horns Rev and Nysted prior to each operation, in order to deter animals to safe distances during pile driving.”

“Only a slight decrease in porpoise abundance was found at Horns Rev during construction and no effect of the operation of the wind farm was seen. A clear decrease in the abundance of porpoises was found at Nysted during the construction and operation of the wind farm. The effect has persisted after two years of operation of the wind farm, with indications of a slow recovery."

The report also includes a discussion on the socioeconomic effects of the projects, as well as a review of public attitudes towards the projects.

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