Orkney Islands SMR

Location and physical characteristics

The Orkney Islands SMR extends around the Orkney Islands, situated immediately north of the Scottish mainland (Figure 1). Strong tidal currents that are some of the fastest in the world, reaching over 8 m/s, run through the Pentland Firth, between the Scottish mainland and the Orkney Islands. Water flows into the northern North Sea around the south and north of the Orkney Islands. The current transports a mixture of low salinity water from the west coast of Scotland and Atlantic water and is generally vertically homogeneous. The surface wave climate in this region (mainly the west coast) is influenced by conditions in the North Atlantic with large regular waves, known as swell. The west is extremely exposed to waves while Scapa Flow for example is more sheltered. This region only has a small amount of local freshwater input.

Sands and gravels notable for their high biogenic carbonate content form the seabed sediments around the Orkney Islands. Much of the gravel around the islands, particularly to the north and east, is composed predominantly of shell debris. These carbonate deposits reflect the rich littoral and sublittoral fauna that exists around the Orkney Islands. Between the main islands the seabed is swept by strong tidal currents. Within these channels, the sediments are thin and patchy, comprising shell-gravels, coarse sand or rock debris; the mud content of the sediments is extremely low. Fine sands are found in sheltered firths or bays. The seafloor of Scapa Flow is covered by a variety of sediments from mud to rock debris. East of Mainland Orkney and to the south of the Orkney Islands, bedrock outcrops occur on the seabed.

Till-like deposits, commonly less than 5 m thick, occur around the Orkney Islands. Thicker deposits occur in the Stormy Bank Basin, south west of Hoy, where up to 50 m thick Quaternary sediments occur locally. Further away from Orkney, to the north west, late Pleistocene deposits of till and mud occur.

Offshore, most solid geology is concealed by seabed sediments, but rock outcrops do occur on the seabed south of Orkney and locally elsewhere. Permian and Permo-Triassic rocks crop out on the seabed in the West Fair Isle Basin and in the West Orkney Basin Complex. An inlier of basement metamorphosed rocks, comprising sandstones, siltstones and shales, as well as mylonites and amphibolites, crops out on North Shoal High.

Figure 1: Orkney Islands Scottish Marine Region. The thicker white line delineates the extent of the Orkney Islands SMR. For a map of all SMRs and OMRs, see Figure 5 here

The Orkney Islands SMR

Coastline length (km) 1,228
Sea area (km2) 9,256
Deepest point (m) 195
Shallowest point (m) coastline
Average depth (m) 65
Tides (m)  0.5 – 3.4
Salinity 34.80 – 34.93
Sea surface temperature (°C) 7.8 – 13.6

  

Productive

Fishing, aquaculture (latter stages of the 20th Century) and now renewable energy production have all been, and continue to be, a feature of life in the Orkney Islands SMR. Tourism is also important to the Orkney Islands SMR, with many tourists arriving by ferry. As an island-community, the sea is very much a part of Orkney life.

 

The Productive Assessment has been undertaken, with a focus on 2014 – 2018, on a sectoral basis. For a number of Sectors, including salmon and sea trout fishing, oil and gas, carbon capture and storage and aggregates, there was no activity within the Orkney Islands SMR during the period 2014 – 2018. However, for many sectors, there were changes over the period 2014 – 2018 (Figure 2).



Figure 2: Changes that have taken place in the Orkney Islands SMR by Sector. Although the period 2014 – 2018 inclusive has been used where possible, there are some entries when a slightly different time period has been used.

Pressures from human activities

As part of SMA 2020, an assessment of the main pressures from human activities in each of the Scottish Marine Regions and Offshore Marine Regions was undertaken through a MASTS-led workshop. The process and outcomes are presented in detail in the Pressure from Activities section. Five main pressures identified for the Orkney Islands SMR ordered as per the MASTS-led Pressure Assessment Workshop were:

Priority [1] Pressure (FeAST classification) [2] Main healthy and biologically diverse components affected [3] Main contributing FeAST activity /activities to pressure [4] Associated productive assessments [5]
1 Removal of target species (including lethal)
  • Fishing - Creeling and potting (FPO)
  • Fishing - Dive fisheries (not including hydraulic dredging) (HF, MIS)
  • Fishing - Pelagic trawling & purse seining (OTM, PTM, TM, PS, PS1, PS2)
  • Fishing - Scallop dredging (DRB)
2 Organic enrichment
  • Aquaculture - Finfish
  • Industrial and agricultural liquid discharges
3 Sub-surface abrasion/penetration
  • Fishing - Scallop dredging (DRB)
3 Surface abrasion
  • Fishing - Creeling and potting (FPO)
  • Fishing - Scallop dredging (DRB)
5 Removal of non-target species (including lethal)
  • Fishing - Creeling and potting (FPO)
  • Fishing - Recreational Fishing
  • Fishing - Scallop dredging (DRB)

Clean and safe

The assessments cover eutrophication, hazardous substances, marine litter, noise and microbiology and algal toxins which have the potential to impact on habitats and species as well as being a consequence of human activity. Although sources of litter or contaminants may be local, there are cases when the source is some distance from the impacted area. The main findings for the Orkney Islands SMR are:

Eutrophication

There was no evidence of eutrophication as a consequence of nutrient enrichment. However, there was a statistically significant increasing trend in nutrient inputs although loads were an order of magnitude lower than for most other SMRs. This increase was attributed to an increase in marine farmed fish biomass in the SMR. Winter nutrient concentrations and chlorophyll concentrations were below assessment criteria and relatively stable. There were no dissolved oxygen data for the Orkney Islands SMR.

Hazardous substances

Hazardous substances (polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and heavy metals (Hg, Cd and Pb)) assessments in sediment and biota (fish and shellfish) were undertaken at the scale of the five Scottish biogeographic regions: Atlantic North-West Approaches, Irish Sea (Clyde and Solway), Minches and Western Scotland, Scottish Continental Shelf and Northern North Sea. The Orkney Islands SMR is in the Scottish Continental Shelf biogeographic region. There are few biota and sediment sites in this biogeographic region, and no sites in the Orkney Islands SMR. However, where assessments were possible, concentrations were generally above background but below concentrations where adverse effects could occur. In addition, there were no increasing trends for most hazardous substances, however, there was a significant increasing trend for cadmium inputs in the Orkney Islands SMR.

A number of biological effects were also measured, and assessments undertaken at the scale of the five Scottish biogeographic regions, however, there are very few sites in the Orkney Islands SMR. Assessment of imposex in dog whelks, an indicator of TBT contamination, included one site in the Orkney Islands SMR. Imposex at this site indicated that concentrations of TBT in the marine environment are causing significant harm (> Environmental Assessment Criteria). The remaining biological effects measurements included in the assessment are from fish and there are no fish sites in the Orkney Islands SMR. At the biogeographic scale, there were insufficient data to assess the other contaminant specific biological effects (PAH bile metabolites and 7- ethoxyresorufin O-deethylase (EROD) activity) in the Scottish Continental Shelf region. External fish disease, a general measure of fish health, was assessed at one site in the Scottish Continental Shelf biogeographic region, and showed that the fish health status was satisfactory However, this site was not in the Orkney Islands SMR.

Marine litter

Due to the lack of assessment criteria for marine litter, beach litter and microplastic, status assessments were not possible. However, litter and microplastics are present in all SMRs, including the Orkney Islands. The Orkney Islands SMR has a relatively low concentration of microplastics in surface water (< 5,000 microplastics per km2 of sea surface).

Seafloor litter was assessed at the scale of the biogeographic regions; the Orkney Islands SMR is included in the Scottish Continental Shelf biogeographic region. The evidence indicates that there are apparent decreases in seafloor litter density over time  between 2012 to 2018.

The Orkney Islands SMR had the lowest average beach litter loadings of all SMRs. Local sources of non-plastic litter items are so low (i.e. wood, paper, cloth, glass, metal, sanitary and medical items) that plastic makes up by far the greatest proportion of Orkney’s beach litter, probably most originating outwith the Orkney Islands SMR. Overall, beaches were relatively clean, with an overall improving trend.

Noise

There are limited noise data for the Orkney Islands SMR; no continuous noise data were collected and there are very few impulsive noise data for this region. It is not possible to do a status assessment as there are no assessment criteria to say what levels of noise are harmful, and not enough years of data to carry out a trend assessment.

Microbiology

A number of marine algal species produce biotoxins which, by accumulation in bivalve molluscs such as mussels and oysters, can cause human illness when these shellfish are eaten. Both biotoxins and phytoplankton are routinely monitored in classified shellfish production areas under Regulation (EU) 2017/625. Such monitoring took place within the Orkney Islands SMR between 2011 and 2014, with concentrations of diarrhetic shellfish toxins exceeding regulatory limits (RL) in 2011 and paralytic shellfish toxins above RL in 2013. No samples were above RL for amnesic shellfish toxins.

Healthy and biologically diverse

This section summarises the information from the Marine Protected Areas (MPAs) and intertidal and continental shelf habitats assessments from SMA2020. It also provides information from the relevant case studies relating to Priority Marine Features (PMFs), with a focus on habitats.  Further work is required to enable assessment at a regional scale for most species; this will be included in Scotland’s next marine assessment.

At the SMR scale for MPAs the focus is on the number of new MPAs, MPAs with new spatial management measures, and MPAs in which spatial management measures are in discussion, as well as recognising monitoring that has been undertaken between 2012-2018.  For the marine habitats, the focus is on interpreting the relevant intertidal and continental shelf habitat assessments – biogenic habitats, predicted extent of physical disturbance to the seafloor  (BH3) and intertidal seagrass beds.  For PMFs, a summary is provided of the changes in our understanding of the habitats of most relevance to the Orkney Islands SMR, including changes in distribution and extent.

Marine Protected Areas

Progress in developing the Scottish MPA network

There are 23 MPAs in the Orkney Islands SMR that contribute to the Scottish MPA network (see Table 1).  Some of these MPAs overlap completely or partially in terms of their spatial coverage and/or the features (habitats, species, etc.) they were set up to help conserve.  They are counted as separate MPAs because they have been established under different legislation which influences the way in which they are managed.  Also note that there are MPAs that straddle the boundaries between different SMRs and OMRs.  Where this is the case, these MPAs have been counted as contributing to the MPA network in all of the SMRs/OMRs in which they are present.  This means that the total number of MPAs in Scotland cannot be calculated through combining the SMR / OMR totals.  Please see the Marine Protected Area assessment which contains statistics for the Scottish MPA network as a whole.  

Table 1. Numbers of types of MPAs in the Orkney Islands SMR that contribute to the Scottish MPA network, including the number of new MPAs introduced since 2012.

Type of MPA

Abbr.

Total no. of MPAs

No. of new MPAs 2012-2018

Nature Conservation MPA

MPA

3

3

Ramsar

-

1

0

Site of Special Scientific Interest

SSSI

5

0

Special Area of Conservation

SAC

4

1

Special Protection Area

SPA

9

0

           

Highlights from the various MPAs include:

The MPAs in the Orkney Islands SMR cover a wide range of natural heritage features including birds, marine mammals, fish, benthic and intertidal habitats, and geomorphological features. North-west Orkney MPA is an important export ground for sandeels which are a critical component of many North Sea food webs. The MPA plays an important role in supporting wider populations of sandeels in Scottish waters. Specifically, newly hatched sandeel larvae from this region are exported by currents to sandeel grounds around Shetland and the Moray Firth.  The MPA also includes geomorphological features representative of the Fair Isle Strait Marine Process Bedforms such as sediment wave fields, sand wave fields and sandbanks. The Wyre and Rousay Sounds MPA was designated for its seabed habitats and geomorphology. Strong tides are squeezed between the islands of Rousay, Wyre and Egilsay creating the perfect conditions for maerl beds and seaweed communities to thrive on the sandy seabed.  Loch of Stennes SAC is the largest brackish lagoon in the UK and is of particular importance on account of its large size, stability, reduced salinity regime and northern location. The salinity gradient within the lagoon supports a range of communities representing sheltered marine, brackish and freshwater conditions.  There are two SACs designated for their seal interest, Faray and Holm of Faray SAC is an important grey seal breeding site, and Sanday SAC for its harbour seal population which has shown a considerable decline in recent years.  There are a large number of internationally important breeding and wintering marine bird SPAs in the Orkney Islands SMR.  Sule Skerry and Sule Stack SPA are two small and remote islands which lie to the west of the Orkney islands.  These islands support large numbers of seabirds, such as northern gannet, common guillemot, Atlantic puffin, European shag, Leach’s petrel and storm petrel, which forage in the waters off the north coast of Scotland.           

Progress in managing MPAs

The progress in implementing management for MPAs in the Orkney Islands SMR is summarised in Table 2.  This includes information on where spatial management measures are in place and where they are under discussion.  It also includes information on the number of MPAs that have been monitored, whether by statutory bodies or through citizen science.

Table 2. Summary of progress in managing Marine Protected Areas in the Orkney Islands SMR. Note that the spatial measures listed in the table are in addition to the protection provided as a result of consideration of activities/developments through licensing and consenting processes. Also, the monitoring of birds, mammals and habitats within SSSIs has been split out to reflect the different programmes of work.  These figures cannot be added together to provide a total number of SSSIs in which monitoring took place because of overlaps in coverage.  

Type of MPA

Spatial measures in place pre-2012

New spatial measures in place 2012-2018

Spatial  measures in discussion 2012-2018

No. of MPAs monitored by statutory bodies 2012-2018

No. of MPAs monitored via citizen science  2012-2018

Nature Conservation MPA

N/A

1

1

1

0

Ramsar

0

0

0

1

0

Site of Special Scientific Interest

0

0

0

Birds

1

Birds

1

Mammals

4

Mammals

0

Special Area of Conservation

0

1

1

Mammals

2

Mammals

0

Special Protection Area

0

0

0

7

0

Within the Orkney Islands SMR there is a fisheries order in place for Wyre and Rousay Sounds MPA and Sanday SAC. The management measures for fishing in this region focus on restrictions to demersal mobile gear.  Further management measures for Papa Westray MPA are under discussion.

During this assessment period the majority of the MPAs have been monitored at least once by the statutory bodies, and some have had multiple visits.  Monitoring has mainly focused on seabirds, wintering waterbirds, and mammals.  Birds have been monitored in a range of different ways, including via a partnership agreement with the RSPB.  As per other SMRs, most of the seal monitoring is undertaken via a partnership agreement between the Sea Mammal Research Unit and NatureScot.

Greater scaup and goldeneye are monitored through Wetland Bird Surveys by the British Trust for Ornithology in the Lochs of Harray and Stenness SSSI.

Information on MPA boundaries can be viewed in Marine Scotland’s NMPi. To find out more about specific MPAs, please visit NatureScot’s SiteLINK.  Detailed reports on habitat monitoring are referenced in Further reading – seabed habitat monitoring reports

Intertidal and continental shelf habitats

SMA2020 contains three relevant habitat assessments: intertidal seagrass beds, subtidal biogenic habitats, and predicted extent of physical disturbance to seafloor.  Assessment of the status of subtidal biogenic habitats is based on temporal reductions in extent of six habitat types: seagrass beds, serpulid aggregations, flame shell beds, maerl beds and horse and blue mussel beds.  Although beds of subtidal seagrass, flame shells, maerl and horse mussels have been recorded within the region, no data are available on temporal changes in extent of these habitats and hence no status assessments could be made.  There are no records of serpulid aggregations or blue mussel beds.  Likewise, intertidal seagrass beds have not been recorded as part of WFD work in the region, and so no analysis could be carried out.  Modelling work was completed as part of the assessment to predict the extent of physical disturbance to the seafloor more generally.

Much progress has been made since 2018 in our understanding of the distribution of flame shell, horse mussel, maerl and subtidal seagrass beds in the region and these are outlined in the section on progress in our understanding of PMF habitats.

Predicted physical disturbance to the seafloor

To assess physical disturbance to seafloor habitats SMA2020 employed a modelling approach which generates a map of predicted relative disturbance levels from demersal fishing activity on a scale of 0 (zero) to 9 (severe).  The map was produced by the combination of information on the distribution of habitats, the sensitivity of the habitats (and species present to varying degrees) and the fishing pressure from demersal trawling, dredging and seine netting.  Fishing pressure information was derived from Vessel Monitoring System (VMS) data from 2012 - 2016 and was categorised as either surface abrasion (disturbance of surface and upper layers of sediment) or sub-surface abrasion (disturbance to a depth of >3 cm).  The final predicted disturbance index utilises the greater of these two pressure values and for descriptive purposes has been categorised as no disturbance (0), low disturbance (1-4) and high disturbance (5-9).

It should be emphasised that this method does not measure disturbance to seabed habitats, but predicts relative levels of disturbance. These relative levels are dependent upon the accuracy of habitat data and sensitivity assessments.  Many of the habitat data are derived from modelling and there is a low level of confidence in its accuracy.  Geographical variation in the accuracy of the sensitivity information employed is likely to be great, being dependent upon the level and quality of information used locally.  A significant limitation of the method is that during the assessment period pressure data were only available for vessels >12 m, which has probably resulted in an underestimation of disturbance for the SMRs.

Predicted habitat disturbance by mobile demersal fishing for the Orkney Islands SMR is slightly lower than the average for SMRs in terms of the proportion of the seabed, with 41% high disturbance compared to the average of 50% for all SMRs (Figure 3).  Ten per cent of the seabed is predicted to experience no disturbance (average of 12% for all SMRs).  The Orkney Islands are surrounded by predominantly sandy and coarse sediment habitats and the disturbance levels closely correspond to the degree of surface abrasion.  Higher disturbance levels are patchily distributed within the region.  The demersal fisheries prohibition within the MPAs came into force in 2016 and so will have had little effect on the assessment, which covered the period 2012 - 2016.