Abstract
The site of the London Array Offshore Wind Farm (OWF) was surveyed in total eight times, once a month between November and February, during the winters of 2010 / 11 and 2011 / 12, using digital high resolution still imagery.
Construction of Phase 1 of the London Array wind farm started in March 2011, Zone 1 was therefore under construction during the 2011 / 12 winter surveys.
One control Zone (Zone 2) was surveyed with the same frequency over the same period, to meet the requirements of the Marine Licence.
Surveys were conducted on a systematic grid of 500 m separation, with images at 3 cm GSD resolution. Average coverage of zones was 15%.
Comparison of results between years showed that overall there were more birds recorded in Zones 1 & 2 during the winter surveys 2010 / 11 (cumulative estimate over four months = 17,628) than there were recorded during the winter surveys 2011 / 12 (cumulative estimate over four months = 8,712).
Fewer divers were recorded in Zones 1 & 2 during the winter surveys 2011 / 12 than there were recorded during the winter surveys 2010 / 11.
Divers arrived at all Zones later during the winter 2011 / 12 (arrived in January / February) compared with winter 2010 / 11 (arrived in November / December).
During the winter surveys 2010 / 11, numbers of red-throated divers counted in Zones 1 & 2 were lowest in November, increased in December and decreased in January. In February numbers peaked with an estimated 9,103 divers in both zones (the peak estimate within the Zone 1 London Array OWF site also occurred in this month).
During the winter surveys 2011 / 12, numbers of red-throated divers counted in Zones 1 & 2 were very low through November and December 2011, increased in January 2012 and peaked in February 2012 with an estimated 2,697 divers in both zones (although peak estimates within the Zone 1 London Array OWF site occurred in January).
The peak number of divers was lower in Zone 1 in 2011 / 12 compared with 2010 / 11, although the peak was higher in Zone 2 in 2011 / 12 compared with the previous year.
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 in Phase 1 in the London Array OWF, etc.
Distribution of divers appeared to reflect shallow water areas. All divers in Zone 1 & 2 were recorded in water < 26 m in depth.
High concentrations of divers were recorded along the north-eastern border of Zone 1 in February 2011 and January 2012, the majority of these birds were outside of the Phase 1 development area. This distribution of divers in Zone 1 was similar to historical layout.
Other bird species / groups recorded included common scoters, fulmars, gannets, cormorants / shags, great crested grebes, great skuas, small gulls (including kittiwakes 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.
Peak abundance estimates increased for four species (seaduck species, fulmars, cormorants / shags and great black-backed gulls) during 2011 / 12 in comparison to 2010 / 11. For all other species, peak abundance estimates were lower during 2011 / 12 in comparison to 2010 / 11.
Marine mammals, likely harbour porpoises, were most abundant during February in Zone 1 during both winter 2010 / 11 and winter 2011 / 12, although the number of individuals estimated to be present was lower during 2011 / 12. In Zone 2 numbers also peaked in February during both survey years. Marine mammal abundance was relatively low across all other survey months during 2010 / 11 and 2011 / 12 in both zones. Across both years, marine mammals were thinly distributed in groups no bigger than two or three.