Prediction of the consequences of wind farm developments for common scoter

Liverpool Bay UK hosts a large population of over-wintering sea ducks (common scoter) that feed upon bivalve prey on the seabed. Windfarm developments have the potential to encroach upon the feeding habitat of common scoter, which may have negative consequences for the bird's fitness if they are excluded from their feeding areas. The current project is designed to predict the extent to which common scoter are affected by wind farm developments.

This project examined the potential effects of the development of offshore windfarms in Liverpool Bay on a sea duck, the common scoter. The Crown Estate, as landowner of the seabed out to the 12 nautical mile territorial limit, plays a key role in the development of the offshore wind industry by leasing areas of the seabed for the placing of turbines. There is a lack of knowledge about the interactions of offshore windfarms and the birds that use such areas of sea, particularly for areas close to the coast. Common scoter may be affected by activities such as the construction and operation of an array of wind turbines in the sea adjacent to their normal feeding areas. A key issue is whether such disturbance would be likely to result in displacement of significant numbers of common scoter being displaced from their normal feeding areas, leading to starvation in winter due to insufficient food, or having to search for longer or further away to find sufficient of their preferred food. Liverpool Bay is the most important known sea area for common scoter around the UK coastline. The population that spends the winter within the bay numbers around 30,000 birds. The common scoter eats certain types of shellfish found in sand on the seabed. Therefore to obtain food, common scoter need to dive to the seabed and search for this food. In order to identify possible feeding areas for the birds, some of the questions that needed to be answered included what is the maximum water depth that common scoter would normally dive to and how long can they search for food at this depth before having to resurface? From observations of numbers and locations of common scoter, with calculations of the water depth (including the effects of tides) and other information it was estimated that the maximum diving depth to find food was approximately 20m. Areas of Liverpool Bay, at or below this depth, were then examined for the existence and amount of the food resources that common scoters eat. An important factor in the study of the behaviour of common scoter is the distance at which they are sensitive to disturbance by shipping or other similar activities, including windfarms. Observations from other studies and from within this project suggest that the disturbance distance is in the range of 1 to 2km, although it is not clear if this distance will reduce with time as the birds become used to an operating windfarm. The effects of actual and proposed windfarm developments in Liverpool Bay were predicted by a computer model. This was developed from a similar model used previously for predicting other environmental effects on wading birds and geese in the areas between high and low water, or on land. The computer model predicts where common scoter would go to if displaced by developments such as windfarms and whether there would be sufficient food resources available within those new locations. The work with the computer model within this project is new and more advanced than anything used previously. However, as with all such modelling exercises, the degree of accuracy of the model in replicating the real world and the size of the uncertainties surrounding the underlying assumptions need to be considered in assessing how likely it is that the predicted outcomes would occur. Even in undisturbed situations a certain proportion of common scoter will die each winter. From published information the natural death rate is estimated to be around 6% and the model output for the 'undisturbed' case gave approximately 7%. In all but one of the combinations of actual, approved and proposed windfarms in Liverpool Bay to which the model was applied there was no significant increase in this natural death rate for common scoter. In just one case, under certain assumed circumstances (all proposed developments, large disturbance distance, etc) the death rate was predicted to increase by a factor of up to two times. The project has provided substantial amounts of new information on this important topic and the outcomes from the project provide useful indications of the potential effects of windfarm developments in Liverpool Bay on common scoter.

Associated publications

Kaiser M.J., Galanidi M., Showler D.A., Elliott A.J., Caldow R.W.G., Rees E.I.S., Stillman R.A. & Sutherland W.J. in press. Distribution and behaviour of Common Scoter Melanitta nigra relative to prey resources and environmental parameters. Ibis, 148: 110-128