Location and physical characteristics
Figure 1: North Scotland Shelf Offshore Marine Region . The thicker white line delineates the extent of the North Scotland Shelf OMR. For a map of all SMRs and OMRs, see Figure 5 here
| Coastal Length | N/A |
| Sea area (km2) | 28,820 |
| Deepest point (m) | 1,073 |
| Shallowest point (m) | 15 |
| Average depth (m) | 213 |
| Tides (m) | 1.6 – 3.5 |
| Salinity | 34.77 – 35.47 |
| Sea surface temperature (°C): | 8.1 – 13.4 |
The North Scotland Shelf OMR is situated to the north of mainland Scotland and the Outer Hebrides and west of Orkney (Figure 1). It is influenced by the oceanic conditions from the adjacent Bailey and Faroe-Shetland Channel, and the coastal conditions that are adverted from the West Highlands and Outer Hebrides SMRs. The residual flow is north-eastward and includes intrusions of warm Atlantic Water onto the shelf. Seasonal variations in circulation in both strength and positioning occur, due to changing wind patterns and water column stratification. In summer frontal jets exist parallel to density fronts between seasonally stratified and permanently mixed waters. The Slope Current, a topographically steered current along the edge of the continental slope (at about the 400-500 m depth contour), which adverts Atlantic waters northwards with speeds up to 0.15 – 0.3 m/s. Along the thermocline, large waves form which can break leading to strong internal mixing and bringing nutrients closer to the surface. The overall surface wave climate is influenced by conditions in the North Atlantic, with a large swell developing at times due to the long fetch.
A range of geological features are present, such as the Solan Bank High which is a Precambrian geological feature of metamorphic basement rock 130 km long and 25 km wide with sections of sand and clay. The region also includes areas of the North Rona, North Lewis, North Minch and West Orkney basins.
Productive
The Productive Assessment has been undertaken, with a focus on 2014 – 2018, on a sectoral basis. For a number of Sectors, including aquaculture, renewables, marine transport and aggregates, there was no activity within the North Scotland Shelf OMR during the period 2014 – 2018. However, for some sectors, there were changes over the period 2014 – 2018 (Figure 2).
The economic contribution of the North Scotland Shelf, in common with some other OMRs, is based around fisheries and oil and gas. Several of the International Council for the Exploration of the Sea (ICES) statistical rectangles occur in the North Scotland Shelf OMR with landings in 2018 for demersal species exceeding 2,000 tonnes.
There are a number of active hydrocarbon fields in the north-west corner of the North Scotland Shelf OMR. Solan was first discovered in 1991. In the last decade, further appraisals of the area resulted in the Strathmore discovery, with the wells tied back to the Solan platform. The field is expected to produce more than 44 million barrels of oil during its production life. The Strathmore discovery is estimated to contain three million barrels of oil equivalent.
Figure 2: Changes that have taken place in the North Scotland Shelf OMR by Sector.
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 North Scotland Shelf OMR 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) |
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| 2 | Removal of non-target species (including lethal) |
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| 3 | Underwater noise |
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| 4 | Physical change (to another seabed type) |
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| 5 | Death or injury by collision below water |
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Clean and safe
The assessments cover hazardous substances and marine litter 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 North Scotland Shelf OMR are:
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. North Scotland Shelf OMR is in the Scottish Continental Shelf biogeographic region. There are few sediment and biota sites in the Scottish Continental Shelf, however, none of these sites were in the North Scotland Shelf OMR. Concentrations of hazardous substances at the few sediment and biota sites in the Scottish Continental Shelf were generally above background but below concentrations where adverse effects could occur at these sites. In addition, concentrations were stable or declining for all hazardous substances measured.
Of the biological effects measurements included in the assessment, there are no sites in the North Scotland Shelf OMR and also limited data at the biogeographic scale region for the Scottish Continental Shelf. External fish disease, a general measure of fish health, was assessed at one site in the Scottish Continental Shelf and showed that the fish health status was satisfactory.
Marine litter
Due to the lack of assessment criteria for marine litter, status assessments were not possible. Seafloor litter was assessed at the scale of the biogeographic regions; North Scotland Shelf OMR is included in the Scottish Continental Shelf biogeographic region. The evidence indicates that there are apparent decreases in sea-floor litter density over time between 2012 to 2018 inclusive for the Scottish Continental Shelf.
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 a OMR 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 North Scotland Shelf OMR, including changes in distribution and extent.
Marine Protected Areas
Progress in developing the Scottish MPA network
There are 5 MPAs in the North Scotland Shelf OMR 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 OMRs or in some cases overlap each other. Where this is the case, these MPAs have been counted as contributing to the MPA network in all of the OMRs in which they are present. This means that the total number of MPAs in Scotland cannot be calculated through combining the OMR and SMR 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 North Scotland Shelf OMR that contribute to the Scottish MPA network, including number of new MPAs introduced since 2012.
|
Type of MPA |
Abbr. |
Total no. of MPAs |
No. of new MPAs 2012-2018 |
|
Special Area of Conservation |
SAC |
3 |
1 |
|
Nature Conservation MPA |
MPA |
2 |
2 |
Note: The Seas off Foula SPA and the West of Scotland MPA were also established in 2020, though both sites have a very small part of their total area within this OMR (less than 2%). Also the Faroe-Shetland Sponge Belt MPA only has 2% of its area within this OMR so is not counted here.
Progress in Managing MPAs
The progress in implementing management measures for MPAs 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, either by statutory bodies or by organisations in partnership with statutory bodies.
Table 2. Summary of progress in managing Marine Protected Areas in the North Scotland Shelf OMR .
|
Type of MPA |
No. of MPAs with spatial measures in place pre-2012 |
No. of MPAs with new spatial measures in place 2012-2018 |
No. of MPAs with spatial measures under discussion 2012-2018 |
No. of MPAs monitored by statutory bodies 2012-2018 |
No. of MPAs monitored by citizen scientists 2012-2018 |
|
Special Area of Conservation |
0 |
1 |
2 |
3 |
0 |
|
Nature Conservation MPA |
0 |
0 |
2 |
0 |
0 |
In the Darwin Mounds SAC, fisheries management measures are in place.
In the other MPAs, progress is ongoing with fisheries management options being developed (Faroe-Shetland Sponge Belt MPA, Solan Bank Reef SAC, the Wyville Thomson Ridge SAC and the West Shetland Shelf MPA).
For the Faroe-Shetland Sponge Belt MPA, a partial site characterisation survey took place in 2018.
Progress in Monitoring MPAs
Information on the evidence base used to characterise the offshore MPAs in the North Scotland Shelf OMR and any subsequent monitoring is given in the Site Information Centre web page ( https://jncc.gov.uk/our-work/offshore-mpas/ ) for the following MPAs:
- Faroe-Shetland Sponge Belt MPA,
- Darwin Mounds SAC,
- Solan Bank Reef SAC,
- Wyville Thomson Ridge SAC,
- West Shetland Shelf MPA.
For links to the MPA surveys and monitoring reports in the Wyville Thomson Ridge SAC and the West Shetland Shelf MPA, see MPA Monitoring Survey Reports | JNCC - Adviser to Government on Nature Conservation
Priority Marine Features
The assessments focus on individual / grouped habitats and species with a number of case studies reflecting more detailed research and monitoring as outlined in ‘What is assessed’. A key component of an OMR is the number and type of Priority Marine Features (PMFs) present in the OMR and the associated protected areas. In addition, there is concern about invasive non-native species and the impact that they are having. With respect to these three aspects, the principal findings of SMA 2020 that are most relevant to the North Scotland Shelf OMR are summarised below.
Number of Priority Marine Features and birds (non-PMF) recorded
The North Scotland Shelf OMR is the location for a range of PMFs as detailed in table 3.
Table 3. Summary of Priority Marine Features in the North Scotland Shelf OMR.
|
PMFs – grouped habitats and species |
No. of species/habitats recorded |
|
Intertidal and continental shelf habitats |
6 |
|
Fish |
26 |
|
Mammals (regularly occurring) |
13 |
|
Shellfish & other invertebrates |
3 |
|
Seabirds (non-PMF) - breeding |
0 |
|
Seaducks, grebes & divers (non-PMF) – non-breeding |
0 |
- There are 48 PMFs in this OMR including a range of shellfish, fish species, marine mammals and deep-sea habitats.
- The combination of seabed type and plentiful supply of nutrients are ideal for the establishment of deep-sea sponges. Up to 50 sponge species can be found within the sponge fields, many of which are different to those found in the surrounding areas. Deep-sea sponge aggregations are an OSPAR Threatened and/or Declining habitat.
- Ideal conditions for the boreal 'ostur' type of deep-sea sponge aggregations to settle are generated by the five different water masses that meet in the Faroe-Shetland Channel, which interact with each other and the continental slope.
- The sponges provide shelter for a range of small sea life such as pencil urchins (Cidaris cidaris) and an elevated perch for animals such as brittlestars that filter food from the passing water currents. Below 800 m, the muddy seabed is home to those species that can tolerate the cooler arctic-influenced waters, such as deep-sea worms.
Distinct sedimentary communities are dominated by contrasting families of polychaete worms. The sedimentary habitats in the MPA also support ocean quahog (Arctica islandica). This species of bivalve mollusc is usually buried in sand or muddy-sand and can regularly live for over 100 years. Ocean quahog are an OSPAR Threatened and/or Declining species.
Climate change
There is good evidence that climate change is driving changes in the physical, chemical and biological conditions of the marine environment but the current evidence base limits the ability to draw conclusions at the scale of the individual marine regions, including North Scotland Shelf OMR. This is a combination of the lack of comprehensive spatial coverage of key monitoring programmes, the relatively short time series, and the complex linkages of climate change impacts in the marine environment.
Increasing concentrations of atmospheric greenhouse gases have caused more energy to be trapped within the Earth’s atmosphere, land and ocean. Approximately 90% of this excess energy has been absorbed by the ocean, resulting in warming ocean temperatures (see Temperature assessment and Climate change Sea temperature assessment).
The increasing concentration of carbon dioxide, one of these greenhouse gases, has the additional consequence of driving a reduction in the pH of the ocean, a process known as ocean acidification (see Ocean acidification assessment and Climate change Ocean acidification assessment).
Mean sea level is rising due to increased contributions of freshwater from melting of land-based ice (glaciers and the polar ice sheets) and due to thermal expansion of water (see Sea level and tides assessment and Climate change Sea level assessment).
The warming temperatures also result in lower oxygen concentrations due to fact that warm water holds less oxygen and changes in stratification further influence oxygen concentrations (see Dissolved oxygen assessment and Climate change Dissolved oxygen assessment). Together with increased metabolic rates in organisms resulting in increased respiration, oxygen depletion has a severe impact on marine organisms due to the impact on metabolic processes.
These changes in the physical environment are also having an impact on marine life, such as changes to their metabolism, changes in seasonality and the timing of events in natural cycles, and changes in their distribution. These changes have consequences for the growth, survival and abundance of species, including those of commercial importance or critical to conservation objectives.
At present, most of these impacts are assessed at scales greater than SMR / OMRs. The Community Temperature Index combines species temperature affinity and their abundances. This index has the potential to inform how communities change due to climate change. An example of changes in the Community Temperature Index from bottom-living fishes can be found in the Fish section within Biological Impacts of Climate Change, where more information on other impacts in marine food webs can be found (such as seabirds and marine mammals) on large regional scales in Scottish waters.
Sea surface temperature in the North Scotland Shelf OMR has increased since 1870 by 0.04 °C per decade on average. The rate of increase has not been constant, and in the last 30 years (1988-2017), the rate of change in temperature was +0.17 °C per decade.
Detecting and understanding long-term change in biological time series is complex and resolving that which is due to climate change remains a challenge. Data from the Continuous Plankton Recorder (1990-2017; see Plankton Assessment) show significant increasing trends in the abundance of diatoms (and specifically pelagic diatoms) and meroplankton (those species who spend part of their life cycle in the plankton community). These trends are significantly correlated to changes in sea surface temperature, used as a proxy for climate change. The Continuous Plankton Recorder data also show a significant decrease in abundance of the dinoflagellate lifeform, although no strong relationship to sea surface temperature could be seen.
Summary
The North Scotland Shelf OMR has seen a 16% increase in the value of the fisheries catch over the five years from 2014-2018. Combined hydrocarbons production increased by 100% (i.e. 1 million tonnes oil equivalent) over the five years 2014-2018.
The five main pressures affecting the OMR are Removal of target species, Removal of non-target species, Underwater noise, Physical change, Death or injury by collision below water. Other pressures identified are Hydrocarbon and PAH contamination, Sub-surface abrasion/penetration, Surface abrasion and Visual disturbance.
No contaminants (i.e. PAHs, PCBs, PBDEs and heavy metals) sampling sites occur the OMR but within the wider Scottish Continental Shelf concentrations were generally above background but below those where adverse effects could occur. Concentrations of those hazardous substances sampled were stable or declining. Evidence indicates there is an apparent decrease in seafloor litter density between 2012-2018.
Three new MPAs were designated between 2012-2018, and new spatial management measures were put in place at one MPA. Spatial fisheries management measures are under discussion for four MPAs. Three MPAs were monitored by statutory bodies during the period 2012-2018.
In the last 30 years sea temperature has risen by 0.17 °C per decade.