DONG Energy has commissioned a consortium of Orbicon and DHI in association with BIOLA to undertake aerial surveys of Common scoter Melanitta nigra and other resting waterbirds as part of the monitoring program for the planned Horns Rev 2 offshore wind farm. This report contains the results of the baseline phase running from October 2007 to April 2008. With respect to resting birds the monitoring program is focused on documenting the use of the planned site by Common scoter. The statistical design of the monitoring program is based on the BACI approach with inclusion of a dynamic habitat model.
The establishment of the Horns Rev 2 offshore wind farm (HR2 OWF) was granted by the Department of Energy on the 19th March 2007 on the basis of DONG Energy‟s application of 13th October 2006. The location of the HR2 OWF is planned for the outer part of Horns Rev, and it consists of a total of 91 turbines, each 2.3 MW which are placed with 13 east-west oriented rows of 7 turbines. The monitoring on resting birds was based on the aerial line transect methodology. Spatial prediction models were developed for Common scoter and Red-throated/Black-throated divers (Gavia stella/arctica) using hydrographical, physical and bathymetric data and modelled distributions of the two key prey species for scoters in this area; American razor clam Ensis americanus and the cut trough shell Spisula subtruncata. The abundance of scoters and divers was estimated for each survey.
Intensive commercial fishing activities were mainly recorded in two zones; the waters deeper than 10 m southeast and northwest of Horns Rev, respectively. These fishing activities affected bird distributions, especially the distribution of Larus-gulls and kittiwakes Rissa tridactyla. The abundance of most species of waterbirds in the area of the planned HR2 OWF was relatively dynamic with large variations in numbers recorded between surveys. Two species groups, however, seemed to use the area more frequently: Red-throated/Black-throated diver and Common scoter. The distribution of Common scoter has changed markedly in the eastern North Sea since 2004. Smaller or larger proportions of birds normally located in the area close to Blåvands Huk from time to time, occurring offshore along the central and western parts of Horns Rev. These general patterns were also recorded during these surveys with medium concentrations of less than 3000 birds, or 10% of the total observed in the area, at the shallow ground VovVov located at the southern periphery of the planned wind farm site. The most significant monitoring result was the findings of the concentration of Redthroated/Black/throated divers at lines crossing or close to the planned wind farm. This result is in line with the survey results from the monitoring programme of Horns Rev 1 and with existing models of diver distribution in the German Bight depicting long-shore aggregations in the same areas coinciding with the long-term mean position of the estuarine front.
Spatial models of the average distribution of Common scoter and divers during the six baseline surveys were developed. The GLM model for scoters indicated that the birds were significantly correlated with the estimated habitat suitability for Spisula subtruncata, with areas close to the coast and areas at longer distances from HR1 OWF. The model indicated high densities (> 100 birds/km2) in the eastern-most part of the modelled area between Cancer and Blåvands Huk, with densities peaking around the 10 m curve off the Danish west coast. The model predicted low-medium densities throughout the rest of the model area, with average densities of scoters in the HR2 OWF ranging between 10 and 40 birds/km2, while densities in the HR1 OWF ranged between 0 and 25 birds/km2. The GLM model for divers indicated that the birds were significantly correlated with the gradient zone between the estuarine water mass and the water mass of mixed North Sea and estuarine water masses from the southern German Bight. The deployment of the model showed enhanced average densities throughout the estuarine gradient zone extending 10-15 km E-W, and areas of higher densities over the western sector of Horns Rev, in the HR2 OWF site and over the plains to the north of here.
The survey data collected in combination with dynamic model data on potential food supply and hydrographic conditions are judged as sufficient for the baseline for the HR2 OWF monitoring programme. As the model data cover the entire period from 2000 to present BACI tests may be designed to include some or all of the data collected during the PSO monitoring programme in the baseline.