Interactions Between Seals and Offshore Wind Farms

McConnell, B.; Lonergan, M.; Dietz, R. (2012). Interactions Between Seals and Offshore Wind Farms (Report No. 978-1-906410-34-6). Report by Aarhus University. Report for The Crown Estate.

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Abstract

Harbour seal (Phoca vitulina) and grey seal (Halichoerus grypus) movement data were collected using telemetry tags from animals hauled out at Rødsand in southern Denmark. These data were combined with similar, but lower temporal resolution, historic data collected in 2009. Rødsand and the neighbouring Vitten-Skrollen are within 10 km of two large wind farms: Nysted and Rødsand II. The aim of this study was to investigate possible interactions between the seals and the wind farms.
A total of 1603 GPS/GSM tagged seals-days of data were obtained from the ten seals (five harbour seals and five grey seals). These produced a total of 69,355 GPS location fixes (an average of 43.3 locations per day). The mean GPS/GSM tag duration was 160 days.
Generally the adult harbour seals remained within 50 km of Rødsand or Vitten-Skrollen haulout sites. In contrast the two juvenile harbour seals (Pv-60265-09 and Pv-02-10) travelled over 200 km to distant haulout sites; north through the Langelands Belt, the Great Belt (Storebælt) and beyond. The grey seals travelled to even more distant haulout sites, up to 500 km away from Rødsand, and eastwards into the Baltic Sea. Both species frequently transited from the two haulout sites through the two nearby wind farms. Visually, there is no obvious interruption of travel at the wind farms’ boundaries.
Interaction was assessed using three analyses: 1. residence times within wind farm zones, 2. a comparison of path speed and tortuosity inside and outside the wind farms and 3. the proximity of individual locations to individual wind farm towers.
All three analyses indicated no significant effect of the wind farms on seal behaviour. This is in accord with another local study of haulout counts that concluded that the wind farms had no long term effect on the local seal population trends.
Caution should be exercised in generalising the findings of this study to other potential sites of interaction. The type of wind farm foundation influences both the construction noise and also any subsequent reef effect. At other seals colonies the different availability of alternative haulout sites and foraging areas may affect their reaction to an altered seascape.