Abundance and activity of harbour porpoises were studied in connection with construction of a small offshore wind farm north of Sprogø, Great Belt, Denmark, within a designated Natura2000 area. The wind farm consists of 7 turbines (2.3MW) on gravitational foundations. Two passive acoustic data loggers, T-pods (Chelonia Ltd.), where placed in vicinity of the wind turbines and two in a reference area 20 km to the north. Monitoring took place over the summer months (April through November) in the years 2008-2010, corresponding to before, during and after construction of the wind farm (BACI design). The data showed very high levels of porpoise activity around Sprogø, higher than the reference site, prior to, during and after construction of the wind farm, consistent with the recognition of the area as being of high importance to porpoises. Acoustic indicators of porpoise abundance (porpoise positive minutes and waiting time between encounters) did not decrease statistically significant during the construction year. This indicates that any effects of the construction was likely very local around the turbine foundations and working vessels. Results support the notion that construction and operation of a small offshore wind farm need not be in conflict with the objectives of a Natura2000 area, given appropriate planning and choice of construction methods. At the stations at Sprogø, data showed pronounced diel variation with a high click activity during night hours (measured as number of click trains recorded), whereas the click activity for the control area showed no clear pattern. A corresponding diel variation in mean inter-click intervals (ICI) within individual click trains was also observed. Thus mean ICI decreased during night hours. Click sequences linked to foraging (feeding buzzes) are characterized by low and decreasing ICIs and the results are thus consistent with an increase in foraging behavior at night.
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26th Annual Conference of the European Cetacean Society, 2012