Abstract
The site of the London Array Offshore Wind Farm plus a buffer around the wind farm (total = ‘zone 1’) in the Outer Thames estuary was surveyed four times (once per month in November, December, January and February) during the winter of 2012 / 13, using digital high resolution still imagery.
A control zone (‘zone 2’) was surveyed with the same frequency over the same period, to satisfy Marine Licence conditions. An additional four control zones (zone 3, 5, 6 & 7) were also surveyed in order to provide information for the wider Ornithological Review Panel process.
Offshore construction for the Phase 1 area of the London Array OWF site commenced in March 2011 and turbines were installed between January to December 2012. Low level activity construction works in Phase 1 are ongoing.
The 2012 / 13 aerial surveys were carried during the second winter of during-construction in Phase 1 London Array OWF site.
Surveys were conducted on a systematic grid of 500 m separation, with images at 3 cm GSD resolution. Average coverage of zones was 18%.
The majority of divers recorded were red-throated divers (97.3%); the remainder were recorded as black-throated divers and great northern divers. The total diver population estimated across all London Array survey zones (zone 1, 2, 3, 5, 6 & 7) was low in November and December 2012, increased in January 2013 and peaked in February 2013 with 5,004 (3,940 – 6,359) estimated divers present.
Distribution of divers appeared to reflect shallow water areas. Approximately 97% of all divers were in water depths of < 20 m.
High concentrations of divers were recorded in the northern part of zone 1 as well as along the north-east border of zone 1 in January and February 2013. This distribution of divers in zone 1 was similar to historical pattern.
Diver abundance and distribution between zones 1, 2 and 3 has changed over the past three years of winter aerial surveys (2010 / 11, 2011 / 12 & 2012 / 13). Peak diver population estimates in zone 1 containing Phase 1 London Array wind farm fell between 2010 / 11 to 2011 / 12 and started to rise again in 2012 / 13, while concurrently peak diver numbers in control zones 2 & 3 increased between 2010 / 11 and 2011 / 12 and then fell again in 2012 / 13.
It would appear that the major increase in red-throated diver numbers that occurred in January 2013 and especially in February 2013 in zone 1 (Table Exec 1) follows the putting in place of the last phase 1 turbine in December 2012. This appears to imply that red-throated divers may rapidly make use of an area once wind farm turbine placement has ceased. Further post-construction surveys would show whether divers continue to increase in zone. Were that to be the case it would be sound evidence that red-throated divers may be less affected by wind farms than previously thought with important implications for consenting.
Large inter-annual variation in recorded diver numbers is common. Reasons for this variation could include effects of weather, natural variation, diurnal distribution, effects of construction etc.
Other bird species / groups recorded in the 2012 / 13 aerial survey included scaup, common scoters, fulmars, gannets, cormorants/shags, grebes, oystercatchers, pomarine skuas, great skuas, small gulls (including kittiwakes, black-headed gulls, little gulls and common gulls), large gulls (including lesser black-backed gulls, herring gulls and great black-backed gulls) and auks (including guillemots, razorbills, little auks and puffins). Gulls were the most abundant species group after divers.
The majority of marine mammals recorded across all zones during the 2012 / 13 aerial survey were cetaceans (77% of total marine mammals); of these, 70% were recorded as dolphins / porpoises with the remainder identified as harbour porpoises. Dolphins / porpoises were most abundant in zone 1 in February 2013 with little use of other zones in other months.