Location and physical characteristics
| Coastline length (km | N/A |
| Sea area (km2) | 59,625 |
| Deepest point (m) | 2,576 |
| Shallowest point (m) | N/A |
| Average depth (m) | 1,386 |
| Tides (m) | 2.5 – 3.0 |
| Salinity | 35.02 – 35.61 |
| Sea surface temperature (°C) | 9.3 – 14.1 |
Figure 1: Rockall Offshore Marine Region. The thicker white line delineates the extent of the Rockall OMR.For a map of all SMRs and OMRs, see Figure 5 here
The Rockall OMR is situated to the west of Scotland and extends from the edge of the Hebrides Shelf across the Rockall Trough and includes the northern part of the Rockall Bank (Figure 1). The topography in this region is diverse featuring the Anton Dohrn seamount, an extinct volcano rising over 1,500m from the deep sediment plains of the Rockall trough, and the steep gradient of the Hebrides shelf and slopes of the Rockall Bank to the east and west.
This OMR also includes the island of Rockall, the remnant of an eroded volcano about 17m high, lying approximately 300km west of Scotland. Tidal variations in the OMR are smaller than most locations on the shelf, due to its oceanic location.
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. Surface waters in the Rockall OMR are typical of the warm Atlantic Water influence. Cold waters fill the deep basins below about 800m; changes in the water properties of these deeper waters are less variable than those at the surface. Intermediate waters lie between this cold deep water and the warmer Atlantic waters above. The Slope Current water (on the eastern edge of the OMR) consists of Atlantic origin waters. The continental slope acts as a transition area between the deeper oceanic waters and the shelf sea waters. Generally, there is a northward flow with warm Atlantic Water and eddies. Cold deep waters from the Faroe–Shetland Channel spill over into the deep basin of the Rockall Trough. East of the Rockall Bank the flow is persistently southward. At Rockall Bank, intensified and faster current speeds can be observed due to this topographic feature. The surface wave climate is influenced by conditions in the North Atlantic, developing a large swell at times ,caused by the long fetch.
As highlighted, a wide range of geological and geomorphological features are represented in this OMR including a volcanic igneous rock protrusion forming the Anton Dohrn seamount, slide deposits which are a characteristic feature along the Hebridean shelf slope and glacial remnant features such as iceberg plough marks. These geological and geomorphological features (the Anton Dohrn Seamount, Hebrides Terrace Seamount and Rockall Bank) create a complex bathymetry over the deep ocean floor, whilst the steep bathymetry of the continental slope acts as a barrier between oceanic regions and the shelf sea systems.
Productive
Rockall OMR is positioned west of the Outer Hebrides. Many of the activities associated with SMRs, for example, tourism, aquaculture, renewable energy production, seaweed production, water abstraction and waste disposal, are absent from Rockall OMR. However, Rockall OMR, like Bailey OMR, is incorporated in the International Council for the Exploration of the Sea (ICES) Areas 6a and 6b. ICES Area 6a sits to the east of 6b and is included with Areas 4 and 3 to make up the Northern Shelf (see fisheries assessment). Cod and haddock are important species for Areas 6a and 6b.
The Productive Assessment has been undertaken on a sectoral basis, with a focus on 2014 - 2018. For a number of Sectors, including aquaculture, oil and gas, renewables and aggregates, there was no activity within the Rockall OMR during the period 2014 – 2018. However, for the fishing sector there was activity over the period 2014 – 2018 (Figure 2).
Figure 2: The offshore nature of Rockall OMR means that in economic terms the primary focus is fishing.
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 Rockall 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) |
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| 2 | Removal of non-target species (including lethal) |
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| 3 | Removal of target species (including lethal) |
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| 4 | Surface abrasion |
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| 5 | Sub-surface abrasion/penetration |
|
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 activities. 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 Rockall 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. Rockall OMR is in the Atlantic North-West Approaches biogeographic region. However, this OMR 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 (e.g. black scabbard, roundnose grenadier and black dogfish) in the Atlantic North-West Approaches biogeographic 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 to higher concentrations in species with the longest lifespans.
Marine litter
Due to the lack of assessment criteria for marine litter and microplastics, status assessments were not possible. However, litter and microplastics are present in all sampled OMRs, including Rockall. There were limited data for microplastics in surface water for this OMR, with data for seven sites sampled in 2020. All but one site had 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; Rockall 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 inclusive for the Atlantic North-West Approaches biogeographic region.
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 Rockall OMR, including changes in distribution and extent.
Marine Protected Areas
Progress in developing the Scottish MPA network
There are 4 MPAs in the Rockall 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 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 Rockall 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 |
2 |
|
Nature Conservation MPAs |
MPA |
1 |
1 |
Note: The West of Scotland MPA, established in 2020, covers most of this OMR.
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 Rockall 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 in 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 |
1 |
0 |
|
Nature Conservation MPAs |
0 |
0 |
1 |
0 |
0 |
In the North West Rockall Bank SAC, the measures currently in place are for a zoned closure to all demersal gears with only a small portion of the site still open to fishing. Fisheries management options are being developed for Anton Dohrn Seamount SAC, East Rockall Bank SAC, and the Barra Fan and Hebrides Terrace Seamount MPA.
Progress in Monitoring MPAs
Information on the evidence base used to characterise the offshore MPAs in the Rockall 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:
- The Barra Fan and Hebrides Terrace Seamount MPA,
- Anton Dohrn Seamount SAC,
- East Rockall Bank SAC,
- North West Rockall Bank SAC.
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 the 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 . With respect to these three aspects, the principal findings of SMA 2020 that are most relevant to the Rockall OMR are summarised below.
Number of Priority Marine Features and birds (non-PMF) recorded
The Rockall OMR is the location for a range of PMFs as detailed in Table 3.
Table 3. Summary of Priority Marine Features in the Rockall OMR .
|
PMFs – grouped habitats and species |
No. of species/habitats recorded |
|
Intertidal and continental shelf habitats |
7 |
|
Fish |
23 |
|
Mammals (regularly occurring) |
13 |
|
Shellfish & other invertebrates |
1 |
|
Seabirds (non-PMF) - breeding |
0 |
|
Seaducks, grebes & divers (non-PMF) – non-breeding |
0 |
- There are 44 PMFs recorded in this OMR including a range of fish, marine mammals and rocky and sedimentary habitats.
- Orange roughy, an OSPAR Threatened and/or Declining species, is associated with seamounts in the region. Orange roughy is a deep-water fish which can live up to 200 years.
- Deep-sea sponge aggregations, also an OSPAR Threatened and/or Declining Habitat, occur within the OMR.
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 SMRs/OMRs,. This is due to 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 single SMRs or 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 Rockall region has increased since 1870 by 0.02 °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 0.13 °C per decade.
Summary
The Rockall OMR value of the fisheries catch remained unchanged at £9 million 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 (light) 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 has been a 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 three MPAs. One MPA was monitored by statutory bodies during the period 2012-2018.
In the last 30 years sea temperature has risen by 0.13 °C per decade.