Scottish Marine and Freshwater Science Volume 5 Number 9: Strategic Surveys of Seabirds off the West Coast of Lewis to Determine Use of Seaspace in Areas of Potential Marine Renewable Energy Developments

1. Executive summary

1.1 By 2020 the percentage of Scotland's energy coming from renewable sources will increase. Studies have identified that there is a need to research how offshore renewable developments affect wildlife populations. The surveys presented here will help to find out how one area of marine development, the west coast of Lewis, is used by waterbirds and marine mammals. Areas close to the Isle of Lewis have already been identified as being important for these groups of animals, through the Special Protection Areas ( SPA) network.

1.2 Methods used during these surveys included a desk-based study, a digital aerial survey and ground-based counts. The digital aerial survey involved an aircraft flying systematic 2km spaced transects through the survey area recording high definition video along four 200m strips thus achieving 10% sampling coverage of the area. The images recorded were processed, and bird and mammal species were identified by analysts post survey and strip transect analysis undertaken to derive abundance estimates for the study area. Density surface modelling was undertaken for fulmars, gannets and auk species.

1.3 Ground-based counts involved an ornithologist undertaking a bird and marine mammal survey from 14 vantage points along the west coast of Lewis. These counts were co-ordinated as much as possible with the aerial survey, and were used to gain more information about more difficult to identify species, or undertaken in places known to be important for seabirds but likely to be missed by the aerial survey. A further vantage point study covering the majority of Loch Roag was also undertaken, covering areas outside the aerial survey study area.

1.4 Aerial and coastal ground-count surveys were undertaken in April, June, July, September and December 2012 and February 2013 with additional surveys of Loch Roag in April, June, July and October 2012 and January and February 2013.

1.5 In April the digital aerial survey recorded 792 birds and 11 mammals from 31 species and species groups. Fulmars were the most abundant bird. In May 347 birds from 24 species and species groups were recorded, with Fulmar again the most abundant bird. In June 491 birds, 24 mammals and one shark were counted, from 41 species and species groups. Fulmars again had the highest count. In July, 525 birds, 15 mammals and one shark were recorded, from 36 species and species groups. In this month gannets were the most numerous bird species. Gannets were again the most commonly recorded bird in September with 247 recorded out of 494 bird records of 25 species or species groups. Five basking sharks were recorded in September, together with eight other marine mammal records. Fulmars were again the most commonly recorded bird species in December 2012 and February 2013 with 133 and 186 records out of 410 and 589 bird records from 22 and 23 species or species groups respectively. The only marine mammals recorded in December and February were two and one harbour porpoises respectively.

1.6 From the west coast of Lewis ground-based counts, a total of 122 birds were counted in April, from 19 species and species groups, in May 145 birds were counted from 18 species and species groups. In June 245 birds and seven mammals from 24 species and species groups were recorded. Recorded bird activity declined in July with 111 birds, three mammals and one shark counted in total, from 21 species and species groups. Fulmars and auks were commonly the most numerous birds counted. 315 birds of 10 species and species groups and eight grey seals and a basking shark were recorded in September, 247 birds of 11 species or species groups were recorded in December with no mammals and the busiest survey was in February 2013 with 655 birds of 12 species or species groups and one grey seal.

1.7 Overall numbers of birds recorded from the aerial and ground counts were low in comparison to numbers of these species breeding on colonies within foraging range.

1.8 Thirty eight species of bird were recorded from the six Loch Roag surveys, including six species of high conservation importance and small numbers of harbour seal and grey seals.

1.9 A comparison of the aerial and ground counts was undertaken. Small sample sizes precluded detailed statistical analysis and the identification of conclusive trends, although some general trends were identified. These included more diving birds such as shags, divers, and auks, particularly black guillemots recorded during ground counts than by aerial surveys, due partly to them spending a proportion of their time underwater in dives and thus unavailable for counting by the almost instantaneous aerial surveys.