This report presents the results from analyses of Nova Innovation’s nine-year programme of land-based marine wildlife observation surveys in Bluemull Sound, carried out as part of the environmental monitoring programme for the Shetland Tidal Array.
Data from a total of 5208 10-minute snapshot scans for birds and 3120 20-minute scans for mammals have been analysed in this report, spanning the nine-year survey period. A total of thirty-three bird, eight mammal and one fish species have been recorded. Fifteen of the bird species and seven of the mammal species are capable of diving to turbine rotor depth (15m below sea level) and therefore ‘at risk’ of near-field encounters with turbines. Only these species were taken through to detailed analysis within this report. Basking shark was also recorded so has been included. A combination of descriptive statistics and modelling techniques have been used to explore the data for these species at risk of near-field encounters with the turbines in the Shetland Tidal Array.
The approach to analysis and interpretation of the vantage point data are based on understanding site-use at different scales, to understand the likelihood or probability of near-field encounters with turbines in the Shetland Tidal Array. Near-field encounters are only possible if a bird or animal uses the site. The likelihood increases if the bird or animal uses the area immediately around the turbines. For birds, this likelihood increases again if the bird dives in the area around the turbine. Dividing the process into these scales, provides useful metrics of the likelihood of near-field encounters, namely a conservative one (large scale), an intermediate one (medium scale) and a realized one (finest scale). The last is a realized one because it is the probability of a bird or animal diving in the immediate vicinity of the turbines. The first is a conservative one, because it acknowledges that any bird or animal in the site could potentially interact with turbines if they choose. These measures provide an understanding of site-use at different scales to understand the probability of encounters between birds and animals with turbines in the Shetland Tidal Array.
Two diving bird species, black guillemot (Cepphus grylle) and European shag (Phalacrocorax aristotelis) accounted for over 90% of all birds recorded in surveys. All other diving bird species were recorded only occasionally in surveys and in generally very low numbers. With the notable exception of Atlantic puffin (Fratercula arctica), which was only present in summer months, most diving bird species were present to some extent throughout the year. Some systematic seasonal variance in occupancy was observed in some species throughout the entire survey area, for example, corresponding with breeding seasons. Birds were generally recorded as solitary individuals or in very small groups in scans, indicating that group foraging does not occur in the site.
Black guillemot, the most frequent and abundant bird species, was recorded in the array area (Zone 1) in 11% of all scans (561 scans of 5208), with birds observed diving in the array area in fewer than 3% of scans (143 scans). The second most frequent and abundant species, European shag, was only recorded in the array area (Zone 1) in <3% of all scans (150 scans), with birds observed diving in the array area in 1% of scans (54 scans). Three of the bird species (gannet, red-throated diver and common guillemot) were each observed diving in the array area in less than 5 occasions over the entire nine-year survey period. This indicates a low level of spatial overlap between diving birds and turbines in the Shetland Tidal Array, even when taking into account the most frequently recorded and abundant species.
Marine animals (mammals and basking shark) were recorded in the surveys relatively infrequently and in low numbers. Some species such as humpback whale (Megaptera novaeangliae), minke whale (Balaenoptera acutorostrata), Risso‘s dolphin (Grampus griseus), killer whale (Orca orcinus) and basking shark (Cetorhinus maximus) were only recorded in one or two scans over the entire nine-year survey period. Atlantic grey seal (Halichoerus grypus), common seal (Phoca vitulina) and harbour porpoise (Phocoena phocoena) were the most frequently recorded species, but seldom recorded in the array area. Both species of seal were normally recorded as individual animals, while harbour porpoise was generally observed in small family groups.
Harbour porpoise accounted for 45% of all mammal sightings in surveys. Despite accounting for this high proportion of overall mammal sightings, harbour porpoise was only recorded in 5% of scans overall (175 scans from a total of 3120) and within the array area (Zone 1) in only 0.71% of scans (22 scans). Common seal accounted for 35% of all mammal sightings but was recorded in just 12% of scans (381 scan). The species was recorded within the array area (Zone 1) in only 0.32% of scans (10 scans). Grey seal accounted for 11% of all mammal sightings and was recorded in 5% of scans (156 scans) and within the array area (Zone 1) in just 0.06% of scans (2 scans). This indicates a very low level of spatial overlap between marine mammals and turbines in the Shetland Tidal Array, even when taking into account the most frequently recorded and abundant species.
The results presented in this report demonstrate that site-use of diving birds, mammals and basking shark in Bluemull Sound is low. This reflects the smaller absolute number of birds and animals occurring within the array area, compared to the wider Bluemull Sound survey area which directly influences impact risk. In the case of birds, very few were observed actively diving within the array area. Encounters with turbines in the Shetland Tidal Array are only possible if a bird or animal uses the site. The likelihood increases if the bird or animal uses the area immediately around the turbines. For birds, this likelihood increases again if the bird dives in the area around the turbines.
The results presented in this report indicate that the likelihood or probability of near-field encounters between all of the diving bird and marine mammal species recorded in the site during the nine-year programme of surveys is very low. For most species, the probability is negligible, but even for the most frequently and abundantly recorded species the risk is still very low ( <5%). This is supported by the findings from analyses of video footage from Nova’s complementary subsea video monitoring programme.