This report summarises preliminary results from a survey carried out in the Horns Reef area in March 2004 and contrast these results to those from a previous survey carried out in February/March 2002. The surveys were designed to analyse the effect, if any, of the construction of a wind farm on sandeels in the area. The 2002 survey was done prior to construction of the wind turbines and the 2004 survey was done after the construction of the wind turbines.
There are no indications that the construction of the wind farm has had any effect on the sediment composition in the impact area (the wind farm area). Especially there was no indication that the content of the finest particles, the Wentworth sediment classes silt/clay and very fine sand, has increased in the impact area from 2002 to 2004. In this respect the construction of the wind farm is not likely to have had any effect on sandeels in the area of the wind farm.
The effect of the wind farm on sandeels was evaluated on the basis of changes in distribution and densities of all species of sandeels combined, as there is no information available to suggest that the possible effects, if any, on sandeels of the construction of a wind farm is dependent on the species.
At all locations fished during both of the years a markedly increase in density of sandeels (all species combined) was observed in the impact area from 2002 to 2004. This increase coincides with a small decrease in densities in the control area (away from the wind farm/impact area). Average densities of sandeels in the impact area increased about 300% from 2002 to 2004, whereas densities decreased about 20% in the control area. It is therefore concluded that the construction of the wind farm has had no negative impact on sandeels in this area.
A large change was found in the species composition and densities of sandeels from 2002 to 2004. The density of A. tobianus and H. lanceolatus increased markedly from 2002 to 2004 whereas the density of A. marinus decreased markedly. The largest increase in densities of sandeels from 2002 to 2004 is due to a large increase in densities in the impact area in 2004 of sandeels smaller than 8 cm (all 1-group sandeels, although there was some uncertainty in the age determination of A. tobianus <6 cm). Of these most of the sandeels smaller than 6 cm were A. tobianus and most of those from 6-8 cm were H. lanceolatus.
The variation in sandeel abundance, which is observed from 2002 to 2004 in the Horns Reef area, is likely to be due to environmental factors influencing recruitment in sandeels. The decrease in A. marinus, observed in the Horns Reef area from 2002 to 2004, may be an example of this as the abundance of A. marinus seems to have followed a similar decrease in most of the North Sea in the same time period.
The possible effect of the wind turbines on sandeel predation mortality was not evaluated in this report, due to a lack of information about changes in diet, distribution, and densities of sandeel predators. Although the influence of environmental factors on recruitment is a likely explanation to the increase in sandeel abundance, observed in the wind farm area from 2002 to 2004, changes in predation mortality may also have contributed to the observed changes in densities.
The sampling design used was found to be appropriate for mapping areas where the distribution of seabirds and sandeels overlap.
Overall, there is no indication that the construction of the wind farm area has had a negative effect on sandeels in this area. There was no indication of an increase in the content of silt/clay and very fine sand in the impact area from 2002 to 2004. Further, there was no indication of a decrease in densities of sandeels (all species combined) in the same area from 2002 to 2004.