Bailey OMR

Location and physical characteristics

Figure 1: Bailey Offshore Marine Region. The thicker white line delineates the extent of the Bailey OMR. For a map of all SMRs and OMRs, see Figure 5 here                   

Sea area (km2) 74,797
Deepest point (m) 2,360
Shallowest point (m) 322
Average depth (m)  1,365
Tides (m) 2.2 – 2.7
Salinity  35.03 – 35.57
Sea surface temperature (°C) 8.9 – 13.5

The Bailey OMR (Figure 1), which incorporates the Rockall Regional Sea, is centred approximately at 59 degrees north. The Bailey OMR extends west from the edge of the Hebrides Shelf across the Rockall Trough and includes the Rosemary Bank Seamount an extinct volcano which towers over 1,000 m above the seafloor and is one of only three seamounts present in Scotland’s seas. The OMR has a complex bathymetry that is broken up by steep ridges (e.g. Wyville Thomson Ridge), the seamounts (e.g. Rosemary Bank) and banks (e.g. George Bligh Bank).

At the OMR’s north-eastern boundary, on the slopes of the Wyville Thomson Ridge, the Darwin Mounds are an extensive area of sandy mounds capped with cold-water coral. The steep bathymetry of the continental slope, where water depths increase from the relatively shallow depths of the continental shelf (~200 m) to the deep Rockall Trough, acts as a barrier between oceanic regions and the shelf sea systems, reducing the amount of exchange of oceanic water into the shallower continental shelf.

Along the thermocline, large internal waves are generated by the tide, which dissipate their energy along the continental slope leading to mixing and the bringing of nutrients closer to the surface. The Slope Current water (on the eastern edge of this region) constitutes the primary northward flow of water on the western edge of the continental shelf (see Circulation Assessment). Cold waters fill the deep basins below about 800 m; the temperature in these deeper waters remains relatively constant separated from the warmer Atlantic waters above by an intermediate layer. The continental slope acts as a transition area between the deeper oceanic waters and the shelf sea waters. Processes that cause mixing of oceanic waters and shelf sea waters are complex but have a significant impact on conditions in Scottish waters.

Cold deep waters from the Faroe-Shetland Channel exist with intermittent overflows through deep channels in the Wyville Thompson Ridge (See Circulation Assessment). As highlighted, there is limited exchange between Atlantic Water and the coastal waters and a generally northward flow with warm Atlantic Water and eddies. The variability in steepness and roughness of the slope influences the cross-slope exchange and slope current stability. The wave climate is influenced by atmospheric conditions in the North Atlantic, and the long fetch results in a large swell developing at times.

The size and shape of the Rosemary Bank seamount influences underwater currents, which bring a plentiful supply of nutrients and food to the area supporting rich seamount communities


Bailey OMR is positioned west of the Outer Hebrides. Bailey OMR forms part of the International Council for the Exploration of the Sea (ICES) areas 6a and 6b.  

The productive assessment has been undertaken on a sectoral basis with a focus on the period 2014 - 2018. For a number of Sectors, including aquaculture, oil and gas, renewables and aggregates, there was no activity within the Bailey OMR during the period 2014 – 2018. However, for the fishing sector, there were changes over the period 2014 – 2018 (Figure 2).

Bailey OMR is positioned west of the Outer Hebrides. Bailey OMR forms part of the International Council for the Exploration of the Sea (ICES) areas 6a and 6b.  

The productive assessment has been undertaken on a sectoral basis with a focus on the period 2014 - 2018. For a number of Sectors, including aquaculture, oil and gas, renewables and aggregates, there was no activity within the Bailey OMR during the period 2014 – 2018. However, for the fishing sector, there were changes over the period 2014 – 2018 (Figure 2).

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 Bailey 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 Physical change (to another seabed type)
  • Fishing - Bottom otter trawling and pair trawls (OTB, OTT, PTB, TB, TBN)
  • Fishing - Demersal seine netting (SSC, SDN, SPR)
2 Removal of non-target species (including lethal)
  • Fishing - Bottom otter trawling and pair trawls (OTB, OTT, PTB, TB, TBN)
  • Fishing - Demersal seine netting (SSC, SDN, SPR)
3 Removal of target species (including lethal)
  • Fishing - Bottom otter trawling and pair trawls (OTB, OTT, PTB, TB, TBN)
  • Fishing - Demersal seine netting (SSC, SDN, SPR)
4 Surface abrasion
  • Fishing - Bottom otter trawling and pair trawls (OTB, OTT, PTB, TB, TBN)
  • Fishing - Demersal seine netting (SSC, SDN, SPR)
5 Sub-surface abrasion/penetration
  • Fishing - Bottom otter trawling and pair trawls (OTB, OTT, PTB, TB, TBN)
  • Fishing - Demersal seine netting (SSC, SDN, SPR)

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 Bailey 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 four Scottish biogeographic regions: Irish Sea (Clyde and Solway), Minches and Western Scotland, Scottish Continental Shelf and Northern North Sea. Bailey OMR is in the Atlantic North West Approaches biogeographic region. However, this region is not included in the MSS contaminants and biological effects sampling plan, due to difficulties sampling in these deep-sea areas.

In addition, there may not be suitable sediment and fish sites in this area. However, PCBs and PBDEs were previously measured in Scottish deep-water fish (black scabbard, roundnose grenadier and black dogfish) in the Atlantic North West Approaches region from 2006 and 2012 (Webster et al., 2014). PCBs and PBDEs were detected, with PCB concentrations being above background but below concentrations where adverse effects could occur, confirming that these contaminants are transported to the Scottish deep-water environment by long range atmospheric transport and accumulate in higher concentrations in species with long lifespans.

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; Bailey OMR is included in the Atlantic North West Approaches 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 SMR/OMR 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 Bailey OMR, including changes in distribution and extent.

Marine Protected Areas

Progress in developing the Scottish MPA network

There are 4 MPAs in the Bailey OMR that contribute to the Scottish MPA network (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 the 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 Bailey OMR that contribute to the Scottish MPA network, including the number of new MPAs introduced since 2012.

Type of MPA


Total no. of MPAs

No. of new



Special Area of Conservation




Nature Conservation MPA




Note: The West of Scotland MPA was also established in 2020 and now covers all of the Bailey OMR. Rosemary Bank MPA has been included in the count of sites as it existed during 2012-2018 but is now part of the larger West of Scotland MPA.

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 Bailey 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






Nature Conservation MPA







In the Darwin Mounds SAC, fisheries management measures are in place. Progress is ongoing for the other sites with fisheries management options being developed for the other 3 MPAs (Wyville Thomson Ridge SAC, the East Rockall Bank SAC and the Geikie Slide and Hebridean Slope MPA).

Progress in Monitoring MPAs

Information on the evidence base used to characterise the offshore MPAs in the Bailey OMR and any subsequent monitoring is given in the Site Information Centre web page ( for the following MPAs:

  • Darwin Mounds SAC,
  • East Rockall Bank SAC,
  • Geikie Slide and Hebridean Slope MPA,
  • Wyville Thomson Ridge SAC.

For links to the MPA Surveys and monitoring reports for the Wyville Thomson Ridge SAC and the Geikie Slide and Hebridean Slope 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 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 Bailey OMR are summarised below.

Number of Priority Marine Features and birds (non-PMF) recorded

The Bailey OMR is the location for a range of PMFs as detailed in Table 3.

Table 3. Summary of Priority Marine Features in the Bailey OMR .

PMFs – grouped habitats and species

No. of species/habitats recorded

Intertidal and continental shelf habitats




Mammals (regularly occurring)


Shellfish & other invertebrates


Seabirds (non-PMF) - breeding


Seaducks, grebes & divers (non-PMF) – non-breeding


  • There are 42 PMFs recorded in this region, including a range of fish, marine mammals and rocky and sedimentary habitats.
  • Deep-sea sponge aggregations comprising low-lying massive and encrusting fields of various sponges (Hexadella, Porifera, Geodia, Thenea, Pheronema, Aphrocallistes and Craniella sponges. Recent studies on Rosemary Bank seamount (McIntyre et al., 2016) estimated around 88 million individual sponges were present in the area.
  • Thickets of the cold-water corals Lophelia pertusa and Madrepora oculate provide a habitat for echiuran worms, brittlestars, brisingiid starfish and sponges. 
  • Extensive areas of stony reef interspersed with gravel areas and bedrock reef support diverse biological communities representative of hard substratum in deep water including a range of sponges; stylasterid, cup and soft corals; brachiopods; bryozoans; dense beds of featherstars and brittlestars; sea urchins, sea cucumbers and sea spiders. 
  • The Seamount communities, deep-sea sponge aggregations and Lophelia pertusa reefs are all considered to be Threatened and/or Declining across the north-east Atlantic by the OSPAR Commission.

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 the Bailey 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 Bailey OMR has increased since 1870 by 0.03 °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 +0.18 °C per decade.


The Bailey OMR has seen a 15% decrease in the value of the fisheries catch over the five years from 2014-2018.

The five main pressures affecting the OMR are Physical change, Removal of non-target species, Removal of target species, Surface abrasion, Sub-surface abrasion/penetration.  Other pressures identified are, Death or injury by collision above water, Death or injury by collision below water, Hydrocarbon and PAH contamination, Litter, Siltation rate changes and Underwater noise.

No contaminant (i.e. PAHs, PCBs, PBDEs and heavy metals) samples were collected from the OMR due to difficulties of sampling.  In the wider Atlantic North-west Approaches biogeographic region the evidence shows there is a decrease in sea-floor litter density between 2012-2018.

Two new MPAs were designated between 2012-2018, and one set of new spatial management measures were put in place.  Spatial fisheries management measures are under discussion for a further three MPAs.  Three MPAs were monitored by statutory bodies during the period 2012-2018.

In the last 30 years sea temperature has risen by 0.18 °C per decade.