Location and physical characteristics
Figure 1: North and West Shetland Shelf Offshore Marine Region. The thicker white line delineates the extent of the North and West Shetland Shelf OMR. For a map of all SMRs and OMRs, see Figure 5 here
| Sea area (km2) | 28,676 |
| Deepest point (m) | 623 |
| Shallowest point (m) | 72 |
| Average depth (m) | 254 |
| Tides (m) | 1.4 – 1.9 |
| Salinity | 34.69 – 35.47 |
| Sea surface temperature (°C) | 7.6 – 13.5 |
The North and West Shetland Shelf OMR covers offshore waters to the north of Scotland and west of the Shetland Isles, bordering three other OMRs (North Scotland Shelf, Faroe-Shetland Channel and East Shetland Shelf) and the Shetland Isles SMR. The residual flow in the North and West Shetland Shelf OMR is northward before it turns southward around the top of Shetland. The Slope Current flows northwards along the edge of the continental slope (at about the 400-500 m contours) with speeds up to 0.15 – 0.3 m/s. In summer, density fronts occur at the transition between permanently mixed waters and those that seasonally stratify due to solar heat input. At this transition, frontal jets occur along the front. The continental slope acts as a transition area between the deeper oceanic waters and the shelf sea waters. Along the thermocline, large internal waves are generated by the tide, which dissipate their energy along the continental slope leading to mixing and bringing nutrients closer to the surface.
The surface wave climate is influenced by conditions in the North Atlantic, developing a large swell at times due to the long fetch.
Productive
The Productive Assessment for the North and West Shetland Shelf OMR was undertaken, with a focus on 2014 – 2018, on a sectoral basis
Demersal fishing has been, and remains, a significant industry in the North and West Shetland Shelf OMR with landings from several International Council for the Exploration of the Sea (ICES) rectangles exceeding 2,000 tonnes in 2018.
The oil and gas industry has been active in this OMR for the past 40 years with the Clair oilfield, discovered in 1977, situated 75 kilometres west of Shetland in water depths of up to 140 metres. It came on stream in the early 2000s. There is significant infrastructure associated with the oil and gas industry, for example, there are currently 1,880 km of active pipelines in this OMR.
For three sectors, fishing, oil and gas and subsea cables, there were changes over the period 2014 – 2018 (Figure 2).
Figure 2: Changes that have taken place in the North and West Shetland 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 and West Sheltand 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 | Surface abrasion |
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| 2 | Sub-surface abrasion/penetration |
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| 3 | Removal of target species (including lethal) |
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| 4 | Removal of non-target species (including lethal) |
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| 5 | Litter |
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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 and West Shetland 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 and West Shetland Shelf OMR is in the Scottish Continental Shelf biogeographic region. There are a few sediment and biota sites in the Scottish Continental Shelf biogeographic region, however ,none of these sites are in the North and West Shetland Shelf OMR. Concentrations of hazardous substances at the few sediment and biota sites in the Scottish Continental Shelf biogeographic region 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 and West Shetland Shelf OMR and also limited data for the Scottish Continental Shelf biogeographic region. Therefore, contaminant specific biological effects (PAH bile metabolites and 7- ethoxyresorufin O-deethylase (EROD) activity) cannot be commented on. 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.
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 and West Shetland Shelf OMR 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.
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 regional 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 North and West Shetland Shelf OMR, including changes in distribution and extent.
Marine Protected Areas
Progress in developing the Scottish MPA network
There are 2 MPAs in the North and West Shetland 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 or SMRs 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 North and West Shetland Shelf OMR 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 |
2 |
2 |
Note: The Seas off Foula SPA was also established in December 2020.
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 by statutory bodies.
Table 2. Summary of progress in managing Marine Protected Areas in the North and West Shetland 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 |
|
Nature Conservation MPA |
0 |
0 |
2 |
2 |
0 |
Progress in Monitoring MPAs
Information on the evidence base used to characterise the offshore MPAs in the North and West Shetland 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,
- North-east Faroe-Shetland Channel MPA.
For links to the MPA Surveys and monitoring reports in the North-east Faroe-Shetland Channel 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 region and the associated protected areas. In addition, there is concern about invasive non-native species and the impact that they are having in any particular region. With respect to these three aspects, the principal findings of SMA 2020 that are most relevant to the North and West Shetland Shelf OMR are summarised below.
Number of Priority Marine Features and birds (non-PMF) recorded
The North and West Shetland Shelf OMR is the location for a range of PMFs in Table 3.
Table 3. Summary of Priority Marine Features in the North and West Shetland Shelf OMR
|
PMFs – grouped habitats and species |
No. of species/habitats recorded |
|
Intertidal and continental shelf habitats |
3 |
|
Fish |
26 |
|
Mammals (regularly occurring) |
12 |
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Shellfish & other invertebrates |
0 |
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Seabirds (non-PMF) - breeding |
0 |
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Seaducks, grebes & divers (non-PMF) – non-breeding |
0 |
- There are 41 PMFs recorded in this region, representing a range of fish species, marine mammals, and shelf habitats such as sand and gravels, bedrock and stony reefs.
- Solan Bank reef is characterised by encrusting flora and fauna such as bryozoans and coralline algae. Areas of flatter bedrock subject to sediment scour have a lower diversity of fauna than more sheltered areas. The highly scoured reef is mainly colonised by the keel worm Pomatoceros triqueter, while a range of sponges, bryozoans and hydroids occur on less scoured reef areas. Water movement created by tidal streams and wave action is greater in shallower areas and here there is a higher abundance of species such as the soft coral Alcyonium digitatum, the cup coral Caryophyllia smithii and the jewel anemone Corynactis viridis. Foliose red algae and kelp grow in the shallowest locations where light penetrates the water.
- The area to the north and west of the Orkney Isles on the Scottish continental shelf is considered important as an export ground for sandeels.
- The range of different types of sand and gravel habitats are an important example of the communities found at the northern extent of their range on the continental shelf in Scottish seas.
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 and West Shetland 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 marine regions. 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 and West Shetland Shelf region has increased since 1870 by 0.05 °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 +0.16 °C per decade.
Summary
The North and West Shetland Shelf OMR has seen a 34% increase in the value of the fisheries catch over the five years from 2014-2018. Combined hydrocarbons production increased by 9% (i.e. 0.5 million tonnes oil equivalent) over the five years 2014-2018. Subsea cables length increased by 3% over the five years 2015-2019.
The five main pressures affecting the OMR are Surface abrasion, Sub-surface abrasion/penetration, Removal of target species, Removal of non-target species, Litter. Other pressures identified are Hydrocarbon and PAH contamination, Introduction or spread of non-indigenous species, Physical change, Physical removal, Reduction in availability or quality of prey, Siltation rate changes (light), Synthetic compound contamination, Transition elements & organo-metal contamination and Underwater noise.
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.
Two new MPAs were designated between 2012-2018, and no new spatial management measures were put in place. Spatial fisheries management measures are under discussion for two MPAs. Two MPAs were monitored by statutory bodies during the period 2012-2018.
In the last 30 years sea temperature has risen by 0.16 °C per decade.