NatureScot Research Report 1005 - Aerial survey of harbour (Phoca vitulina) and grey seals (Halichoerus grypus) in Scotland in 2016: Orkney and the North Coast, the Moray Firth and part of East Scotland

SMRU undertakes routine surveys of harbour and grey seals around Scotland and in part of England. These surveys provide the basis of the information the Natural Environment Research Council is obliged to submit to the Scottish Government and to the Department of the Environment, Food and Rural Affairs (Defra) under the Marine (Scotland) Act 2010 and the Conservation of Seals Act 1970 respectively, on the size, distribution and status of UK seal populations. The most recent advice can be found. The surveys also provide information required by Scottish Natural Heritage to satisfy obligations under the EU’s Habitats Directive on reporting the conservation status of seals within Special Areas of Conservation (SACs) and more broadly across Scotland.

 In the UK, harbour seal population surveys are carried out during their annual moult, in August. In Scotland, the seven Scottish Seal Management Areas (Figure 1) making up the entire coast are surveyed approximately on a five-year cycle, although surveys are carried out annually in the Moray Firth and the Firth of Tay & Eden Estuary (Figure 2). Harbour seals in part of the Moray Firth are also surveyed annually during their breeding season, between mid-June and mid-July.

Grey seals hauled ashore are counted during all harbour seal surveys. Grey seal numbers can be highly variable from day to day during the summer months but these surveys do provide useful information on their summer distribution. The August grey seal counts are also used as an independent estimate to inform a more detailed population estimate that is derived from counts of pups born during the autumn grey seal breeding season (Lonergan et al., 2011; Russell et al., 2017)

This report summarises the results from August 2016 surveys of harbour and grey seals in Orkney, on the north coast of Scotland, in the Moray Firth and on the east coast of Scotland (from Fraserburgh to North Queensferry, including the Firth of Tay and Eden Estuary). The surveys were carried out to obtain updated estimates of the numbers of harbour and grey seals in the seven Scottish Seal Management Areas (Figure 1) and form the start of a new round-Scotland survey. The previous round-Scotland survey was carried out between 2011 and 2015 (Duck & Morris, 2012; 2013; 2014; 2015; 2016). The results from the 2016 survey are presented within the context of the previous survey results from 2011 to 2015 and within the longer term trends.

The Sea Mammal Research Unit (SMRU) carried out most surveys of harbour seals by helicopter using a thermal imaging camera. In estuarine areas (Moray Firth and Firth of Tay & Eden Estuary), a small fixed-wing aircraft without a thermal imaging camera was used. Oblique high-resolution digital images were taken during all flights, and all surveys followed the standard SMRU survey protocol: 

• Surveys were restricted to within two hours either side of low tides occurring between 12:30 and 19:30 (approximately). 
• Surveys were restricted to the August harbour seal moult.  There was no surveying on rainy days. 
• High resolution digital photographs were taken of almost all groups of seals on shore. 
• During the helicopter surveys, initial counts were made in real time and subsequently confirmed or corrected by reviewing the thermal image footage in conjunction with the high-resolution digital images.

All maps were produced using Manifold System 8.0 Ultimate Edition. The coastlines were drawn using Global Self-consistent, Hierarchical, High-resolution Shoreline data (Wessel & Smith, 1996), available to download from the National Geophysical Data Center website and high-resolution Scotland mean high and low water shape-files based on Ordnance Survey data (Pope, 2011).

2.1 Helicopter & thermal imager surveys in August 2016

Figure 3 shows the sections of coasts that were surveyed on different days: 

1 Aug 2016: south Orkney 

2 Aug 2016: mid and south Orkney 

3 Aug 2016: weather day, low cloud 

4 Aug 2016: north Orkney 

5 Aug 2016: north Scotland, north and mid Orkney 

9 Aug 2016: part Moray Firth, part east Scotland 

10 Aug 2016: part Moray Firth

3.1 Scotland - composite

 Figure 2 shows the years in which different segments of the Scottish coast were surveyed most recently, between 2011 and 2016. (Note that a small section of the north Moray Firth coast, from Wick to Duncansby Head, was last surveyed in 2008 when only one harbour seal and seven grey seals were counted). 

2008: Duncansby Head to Wick

2011: Western Isles, Moray Firth (Wick to Helmsdale section) 2013: East Scotland (Aberlady Bay to North Queensferry section), West Scotland (Cape Wrath to Ullapool section) 2014: West Scotland (Ullapool to Scarba in the Firth of Lorn section) 

2015: East Scotland (border to Aberlady Bay section), West Scotland (Firth of Lorn to southern tip of the Mull of Kintyre section), South-west Scotland, Shetland 

2016: Orkney and North Coast, Moray Firth (Helmsdale to Fraserburgh section), East Scotland (Fraserburgh to North Queensferry section)

Figure 3 shows the sections of coast surveyed in August 2016. 

The distribution of harbour seals in Scotland from these most recent August surveys is shown in Figure 4. Counts have been aggregated by 10 km squares in order to show the general August distribution more clearly. The numbers of harbour seals counted in Seal Management Areas in Scotland are given in Table 1. From the most recent surveys of the Scottish coast, a total of 25,149 harbour seals were counted between 2008 and 2016 (Duck & Morris, 2012; 2013; 2014; 2015).

The total count is similar to the previous round-Scotland total of 25,399 (2011-2015; Duck & Morris 2016), and is lower than the 1996-1997 total of 29,514, following large declines in northern and eastern areas. West Scotland is now by far the most important Management Area in terms of number of harbour seals in Scotland. 

Figure 5 shows the summer distribution of grey seals in Scotland. In 2011, there was a very low grey seal count for the Monach Isles, off North Uist, which was likely due to the sunny day and high ambient temperatures (Duck & Morris, 2012). Large numbers of grey seals were observed in the water close to haul-out sites but, because they were not on land, were not included in the count. Since this consistently high count was ‘missing’ in 2011, data for the Monach Isles from a fixed-wing survey of the more distant offshore islands carried out in August 2014 (SMRU unpublished data) are used here instead.

The numbers of grey seals counted in Seal Management Areas in Scotland are given in Table 2. The numbers of grey seals hauling out can be highly variable in the summer months and caution is advised when interpreting August counts of grey seals. None the less, these counts are used elsewhere to refine estimates of the size of the UK grey seal population (Lonergan et al., 2011; Russell et al., 2017). 

Figure 6 shows the trends in numbers of harbour seals counted in all Seal Management Areas in Scotland since 1996. Three points have been added for 2016: for Orkney and the North Coast, for the Moray Firth and for East Scotland. Most plotted points are an amalgamation of counts from different years. New points are added only in years when significant new data are available. There is a marked difference in the trajectories of counts from the west of Scotland (general increase) compared with counts from Orkney and the north and east coasts of Scotland (general decline).

3.2 Area summaries 

3.2.1 Orkney and North Coast

Orkney and the north coast of Scotland were surveyed between 1st and 5th August 2016. In Orkney, 1,240 harbour seals were counted (Table 3; Figure 7) with 109 counted on the north coast of Scotland (Table 3). The 2016 harbour seal count for Orkney was the lowest recorded by SMRU and was 34% lower than the previous (2013) count of 1,865, equivalent to an average annual decline of 13%. The 2016 count is 85% lower than the (1997) highest count of 8,522. Counts of harbour seals in subregions of Orkney and the North Coast are in Table 3. In 14 of the 21 subregions in Orkney, SMRU counted the lowest numbers of harbour seals since 1985; four of these were zero counts (Table 3). Three of the remaining seven subregions had single figure counts (Table 3). The decline in harbour seal numbers in Orkney, first noticed in 2006 (Lonergan et al., 2007), is clearly continuing. Figure 8 shows a comparison of numbers of harbour seals counted in Orkney in 1997 (highest count) and in 2016 (lowest count).

The distribution of grey seals in Orkney is shown in Figure 7 with subregion counts from Orkney and the North coast in Table 4. Counts of grey seals in Orkney do not show any great change, other than the very low count in 2001, which was likely due to a period of prolonged wet weather.

3.2.2 Sanday, Orkney

Sanday was surveyed on 4th August 2016. Figure 9 shows the distribution of harbour and grey seals on Sanday in August 2016. A total of 83 harbour seals were counted on Sanday, the lowest count recorded by SMRU (Table 3 & Table 5). Of these, 74 were within Sanday SAC (Table 5; Figure 9). The 2016 harbour seal count represents a decline of 27% since 2013 (114) for the whole of Sanday and a decline of 25% within the SAC (99). 

A total of 506 grey seals were counted on Sanday in August 2016, of which 486 were within the harbour seal SAC (Figure 9; Table 4 & Table 6).

3.2.3 Moray Firth 

The greater part of the Moray Firth, from Helmsdale to Fraserburgh, was surveyed on 9th and 10th August 2016. The distribution of harbour and grey seals in the Moray Firth is shown in Figure 10. The numbers of harbour seals counted in different parts of the Moray Firth are 4 in Table 7 and are shown as histograms in Figure 11. A total of 940 harbour seals were counted in the Moray Firth compared with 745 counted in 2015. New lowest counts of harbour seals were recorded in the Dornoch Firth and Morrich More SAC (85) and in the Beauly and Inverness Firths (30), while highest counts were recorded at Culbin and Findhorn (484) and between Burgh Head and Fraserburgh (47). 

Detailed counts of grey seals in the Moray Firth are in Table 8 and a histogram of these counts in Figure 12.

3.2.4 East Scotland 

The coast of East Scotland, from Fraserburgh to North Queensferry was surveyed on 9th August. The survey was curtailed at North Queensferry by rain approaching from the upper reaches of the Firth of Forth. Combined with data from 2013 (Aberlady Bay to North Queensferry) and 2015 (Border to Aberlady Bay) surveys, 368 harbour seals were counted in the East Scotland Seal Management Area (Table 1). Of these, 51 were in the Firth of Tay and Eden Estuary SAC (Table 1), approximately 8% of the mean count between 1990 and 2002 (641). Detailed counts of harbour seals within the Firth of Tay and Eden Estuary SAC are in Table 9 with counts of grey seals in Table 10. A map showing the distribution of harbour and grey seals in the Firth of Tay and Eden Estuary is in Figure 13. Histograms of harbour seal counts are in Figure 14 and of grey seal counts in Figure 15. 

3.3 Harbour seal SACs 

Three harbour seal SACs were counted in 2016: Sanday, the Dornoch Firth and Morrich More, and the Firth of Tay and Eden Estuary. August counts of harbour seals in SACs in Scotland are in Table 11 with the trajectories of the counts in Figure 16. With the exception of the three SACs in West Scotland (South-east Islay Skerries, Lismore and Ascribs & Dunvegan), the numbers of harbour seals counted in Scottish harbour seal SACs has declined considerably since the sites were first designated. Mousa in Shetland, Sanday in Orkney, the Dornoch Firth and Morrich More and the Firth of Tay and Eden Estuary show the biggest declines. The most recent individual counts for each of these SACs are less than 100.

This report provides the results of the first year of a four year programme of surveys that aim to cover the entire coastline of Scotland to provide the most up-to-date assessment of the harbour seal population. 

The 2016 counts indicate that the decline in harbour seal numbers in Orkney continues, whilst numbers in the Moray Firth show a modest increase from the previous count, and numbers in east Scotland remain at historically low levels. Within SACs designated for harbour seals, new counts were obtained for Sanday SAC, the Dornoch Firth and Morrich More SAC, and the Firth of Tay and Eden Estuary SAC.

Areas to be surveyed by SMRU in 2017 and 2018 include West Scotland, Western Isles, South-West Scotland, and part of East Scotland Management Units. In August 2019, SMRU propose to survey Shetland and Orkney to complete the four year programme of surveys covering the entire Scottish coastline. Once all the fieldwork and analyses are completed, the results from the full cycle of surveys (2016– 2019) will be collated in a single report.

Duck, C.D. & Morris, C.D. 2012. Surveys of harbour (common) and grey seals in the Outer Hebrides and the Moray Firth in August 2011. Scottish Natural Heritage Commissioned Report No. 518. 

Duck, C.D. & Morris, C.D. 2013. Surveys of harbour (common) and grey seals in Orkney, the north coast of Scotland, the Moray Firth and the Firth of Tay in August 2012. Scottish Natural Heritage Commissioned Report No. 572. 

Duck, C.D. & Morris, C.D. 2014. Surveys of harbour (common) and grey seals on the east, north and north-west coast of Scotland and in Orkney, including the Moray Firth and the Firth of Tay, in August 2013. Scottish Natural Heritage Commissioned Report No. 759. 

Duck, C.D. & Morris, C.D. 2015. Surveys of harbour and grey seals in West Scotland (Ullapool to Scarba), in the Moray Firth and in the Firth of Tay, in August 2014. Scottish Natural Heritage Commissioned Report No. 869. 

Lonergan, M., Duck, C.D., Thompson, D., Mackey, B.L., Cunningham, L. & Boyd, I.L. 2007. Using sparse data to investigate the declining abundance of British harbour seals. Journal of Zoology, 271, 261-269.

 Lonergan, M., Duck, C.D., Thompson, D., Moss, S. & McConnell, B. 2011. British grey seal (Halichoerus grypus) abundance in 2008: an assessment based on aerial counts and satellite telemetry. ICES Journal of Marine Science, 68, 2201-2209. 

NOAA National Geophysical Data Center, GSHHG, Downloaded September 2010, 

Pinn, E, 2009. Threshold for Designation of Special Areas of Conservation for Harbour Porpoise and Other Highly Mobile, Wide Ranging Marine Species. Annex 1 to JNCC Committee Paper P10Sept08, amended 13 February 2009. 

Pope, Addy, “Scotland Mean High and Low Water” [Shapefile geospatial data], contributed 02/02/2011. Using: EDINA Digimap ShareGeo facility. Downloaded: October 2011. 

Russell, D.J.F., Duck, C.D., Morris, S.D. & Thompson, D. 2017.Independent estimate of grey seal population size: 2008 and 2014. SCOS Briefing Paper 16/03.  

Wessel, P. & Smith, W.H.F. 1996. A global self-consistent, hierarchical, high-resolution shoreline database. Journal of Geophysical Research, 101, 8741-8743.