Large-scale feature case studies
14th and 15th March, 2012
Heriot-Watt University, Edinburgh
Contents
Page no.
INTRODUCTION .............................................................................................................. 1
LARGE-SCALE FEATURE CASE STUDIES ................................................................... 2
FRONTS AND OTHER HYDROGRAPHIC PROCESSES ............................................. 2
SHELF DEEPS.............................................................................................................. 6
SHELF BANKS AND MOUNDS..................................................................................... 9
CONTINENTAL SLOPE ................................................................................................ 12
SEAMOUNTS................................................................................................................ 15
INTRODUCTION
In response to comments received at the third stakeholder workshop, this document has
been produced to help explain how large-scale features are being used in the context of
identifying Nature Conservation MPAs in Scotland’s seas.
Five large-scale features are included on the list of MPA search features: seamounts;
continental slope; shelf deeps, shelf banks and mounds; and fronts and other hydrographic
processes. These features have been included on the list of MPA search features in order to
help build ecosystem function into the development of the MPA network.
Large-scale features are intended to complement other MPA search features by helping to
identify areas of wider functional significance within Scotland’s seas. This may be through
taking into account ecological and geomorphological processes of importance to MPA
search features or the wider marine environment. Large-scale features may also help enable
consideration of connectivity within the network where they play a role in providing key
linkages between different features. Specific large-scale features may contribute to the
network through supporting species at a range of trophic levels, for example from areas of
high primary productivity through to aggregations of mobile top predators.
This type of approach is inherent in the Scottish MPA Selection Guidelines, most notably in
guideline 1c which looks at the inclusion of areas of functional significance to the overall
health and biodiversity of Scotland’s seas; guideline 2a which looks at the inclusion of
combinations of features which are functionally linked; and guideline 5 which looks at
connectivity across the network.
Five case studies are presented in this report; one for each of the large-scale features. The
case studies provide an overview of the known distribution of each large-scale feature, what
is known about their general characteristics, and what we know about their functional
importance in terms of the key supporting role they play, their functional links to top marine
predators, and how they might provide connectivity.
The aim of these case studies is to illustrate how each type of large-scale feature could help
contribute to wider ecosystem function within Scotland’s seas.
The references to geographical examples are illustrative and do not imply MPA search
locations. Further work is being done to consider how large-scale features would be
protected via designation as a protected area.
1
LARGE-SCALE FEATURE CASE STUDIES
FRONTS AND OTHER HYDROGRAPHIC PROCESSES
Distribution of fronts and other hydrographic processes in Scottish waters
Persistent fronts occur on the west
coast from the Clyde Front to the
south-east of Islay (the Islay Front) as
well as to the south-west of Tiree.
Fronts also exist around the Northern
Isles (Orkney-Shetland front), and in
the North Sea (e.g. Aberdeen-Buchan
front).
The mapping shows the distribution of
surface thermal fronts only, based on
a mean seasonal persistence
threshold of 50%.
Map © Crown Copyright. UK Limits provided by UKHO Law of the Sea Division. All rights
reserved. Ordnance Survey Licence number SNH 100017908. 2011
General characteristics of fronts and other hydrographic processes
Description - Fronts form the boundaries between masses of water, for example where
tidally mixed coastal waters meet thermally stratified offshore waters, or where fully saline
oceanic waters meet lower salinity inshore water. In Scotland’s seas, tidal mixing fronts tend
to form in summer months, when the weather is typically more settled allowing waters away
from the coast to stratify, while salinity fronts are observed where there is a greater oceanic
influence or where freshwater runoff occurs, for example at the mouths of estuaries and sea
lochs. The interaction between oceanic currents and topographic features, such as islands,
seamounts, banks, deeps and channels can also generate persistent localised fronts and
other hydrographic features such as eddies and internal waves.
Functional importance - Persistent hydrographic features, such as fronts, are widely
recognised as supporting enhanced biological activity. Mixing at the boundary between two
water bodies may lead to elevated primary and secondary production and as a result can
serve to aggregate prey species (Hyrenbach et al., 2000). In turn top predators, such as
seabirds, marine mammals and predatory fish, are attracted to prey aggregations. Areas
with persistent hydrographic features may therefore have a wider functional role for the
health and biodiversity of Scotland’s seas. Sharp gradients in temperature and salinity, as
are characteristic of fronts, may also result in these areas being used as migration corridors
or potentially delineate boundaries for some species if they are near the edge of their range.
Fronts and other hydrographic processes also play an important role in the circulation and
ecology of Scotland’s seas and more widely.
Functional importance of fronts and other hydrographic processes
Key supporting role - At tidal fronts, for example, the convergence of nutrient rich coastal
waters and clear, stratified offshore waters can result in high productivity. Marked chlorophyll
maximums have previously been reported from within frontal gradients (Holligan 1981), with
peak chlorophyll values recorded slightly offshore from the front itself (Pingree & Griffiths,
1978; Franks, 1992 and references cited within). Distributions of zooplankton, an important
component in the diets of many fish and seabirds, reflect patterns in abundance of
phytoplankton prey and therefore may also be concentrated in frontal zones.
Distributions of the early stages of fish have been linked to fronts. Across the North Sea,
2
Munk et. al. (2009) observed that egg- and early larval distributions of cod, plaice and lesser
sandeel show a high degree of spatial and temporal overlap, with peak eggs abundances
found in areas of stronger frontal gradients. In other parts of the world river plumes and
associated salinity fronts have been found to be important for the early life stages of fish
(Grimes & Finucane, 1991; Grimes, 2001). Pre-spawning herring aggregations in the
northern North Sea are shown to be correlated with zooplankton-rich waters associated with
frontal zones (Kiorboe & Johansen, 1986; Maravelias & Reid, 1997). Kiorboe & Johansen
(1986) suggest that frontal water may provide the best long-term average feeding conditions
for herring larvae. Settled sandeel distribution is largely explained by the presence of coarse
sand sediments (Wright et al., 2000), but this species often feeds on plankton concentrated
in nearby frontal features at the edge of sand banks.
Basking shark distribution is also related to the presence of fronts, where nutrients and
zooplankton prey are concentrated (Sims and Quayle 1998). Tagging data, for example,
shows an individual basking shark spent time in deeper water around the Islay front on the
west coast (Ormond & Gore, in prep.).
Functional links to top predators - Marine predators including cetaceans, seals and a
range of seabird species are attracted to frontal regions. It is likely that these features
influence top predators indirectly through effects on prey distribution (Davis et al., 2002).
Summer distribution of minke whales in the outer Moray Firth, for example, is correlated with
the presence of a warm water plume (Tetley et al., 2008), which is thought to generate
increased productivity and in turn may support higher numbers of sandeels. Minke whale
distribution has also been directly linked to areas of suitable sandeel habitat (Robinson et al.,
2009). Distribution of common dolphins in the Celtic and Irish Seas has been shown to be
associated with a frontal system known as the Celtic Sea front (Goold, 1998), while whitebeaked dolphins have also been observed in association with fronts and foraging seabirds in
the Barents Sea (Mehlum et al., 1998).
Seabirds are well known to forage in association with hydrographic features. At the
Aberdeen Front, for example, fulmars were present in high numbers along the boundary of
the front and on the seaward side, but not in mixed waters toward the coast, effectively
demarcating the position of this feature (Camphysen & Garthe, 1997). Camphuysen & Webb
(1999) report very high densities (sometimes >1000/km2) of foraging seabirds, dominated by
kittiwake, guillemot and razorbill, within a relatively narrow strip of water that coincides with
the frontal zone between thermally mixed coastal waters and stratified offshore waters. On
the west coast, razorbills were associated with the presence of the Clyde front during the
early breeding season (Webb et. al. 1990). Although species with different foraging
strategies respond differently to fronts, all benefit from the predictable foraging opportunities
that these features provide.
Scott et al. (2010) found that distribution of several species of top predators foraging in the
Firth of Forth was partially explained by the presence of sub-surface chlorophyll, thought to
be linked to mixing caused by internal waves. It is possible that these processes function
either to increase productivity in the region or make prey more available (Scott et al., 2010).
Mixing at frontal regions could have similar implications.
Connectivity - It is expected that residual currents and seasonal frontal jets (Hill et al.,
2008) play a role in terms of connectivity and may be important for different life stages of
various species (e.g. through larvae retention or drift toward suitable spawning habitat,
foraging patterns in top predators). However, there is currently limited evidence available to
understand these processes and their potential function.
3
Issues and opportunities
Additional work is underway to better define fronts and other hydrographic processes and
understand their functional importance. This includes further interpretation of the ocean
thermal front mapping to improve our understanding of these processes. A complimentary
piece of work to identify fronts based on high resolution ocean colour imagery is also
underway and will help identify surface or near-surface fronts that do not necessarily have a
thermal signature, as well as delineate finer scale hydrographic features closer to the coast.
These analyses will provide reasonable representation for surface fronts, but do not well
represent sub-surface hydrographic processes.
Sub-surface or bottom fronts are also thought to be of importance, but the data available to
support their interpretation at a national level may not be of suitable resolution. Regional
data on sub-surface fronts, where available, has yet to be interpreted in the context of the
Scottish MPA Project, but will be considered for its applicability to inform further assessment
of specific locations.
Other projects proposed to be carried out this year, for example modeling of critical habitat
for cetaceans, may also benefit our interpretation of fronts and other hydrographic
processes.
References
Camphuysen, K.C.J. and Garthe, S. (1997). An evaluation of the distribution and scavenging habits of
Northern Fulmars (Fulmarus glacialis) in the North Sea. ICES Journal of Marine Science 54, 654683.
Camphuysen, K.C.J. & Webb, A. (1999). Multi-species feeding associations in North Sea seabirds:
jointly exploiting a patchy environment. Ardea 87:177-198.
Davis, R., Ortegaortiz, J., Ribic, C., Evans, W., Biggs, D., Ressler, P., Cady, R., Leben, R., Mullin, K.
and Wursig, B. (2002). Cetacean habitat in the northern oceanic Gulf of Mexico. Deep Sea
Research Part I: Oceanographic Research Papers 49(1); 121-142.
Franks, P.J.S. (1992). Phytoplankton blooms at fronts: patterns, scales and physical forcing
mechanisms. Reviews in Aquatic Sciences 6:121-137.
Grimes, C.B. (2001). Fishery Production and the Mississippi River Discharge. Fisheries 26(8); 17-26.
Grimes, C.B. and Finucane, J.H. (1991). Spatial distribution and abundance of larval and juvenile fish,
chlorophyll and macrozooplankton around the Mississippi River discharge plume, and the role of
the plume in fish recruitment. Mar. Ecol. Prog. Ser. 75: 109-119.
Goold, J. C. (1998). Acoustic assessment of populations of common dolphins off the west Wales
coast, with perspectives from satellite infrared imagery. Journal of the Marine Biological
Association of the UK 78; 1353−1364.
Hill, A.E., Brown, J., Fernand, L., Holt, J., Horsburgh, K.J., Proctor, R., Raine, R. and Turrell, W.R.
(2008). Thermohaline circulation of shallow tidal seas. Geo Res Let 35, L11605,
doi:10.1029/2008GL033459
Holligan, P.M. (1981). Biological Implications of Fronts on the Northwest European Continental Shelf.
Philos. Trans. R. Soc. London A 302 (1472); 547-562.
Hyrenbach, K., Forney, K. and Dayton, P. (2000). Marine protected areas and ocean basin
management. Aquatic Conservation: Mar. Freshw. Ecosyst. 10: 437-458
Kiorboe, T. and Johansen, K. (1986). Studies of a larval herring (Ciupeaharengus L.) patch in the
Buchan area. IV. Zooplankton distribution and productivity in relation to hydrographic features.
Maravelias C.D. and Reid, D.G. (1997). Identifying the effects of oceanographic features and
zooplankton on prespawning herring abundance using generalized additive models. Mar Ecol Prog
Ser 147: 1-9.
Mehlum, F., Hunt G.L., Decker, M.B. and Nordlund, N. (2008). Hydrographic Features, Cetaceans
and the Foraging of Thick-Billed Murres and Other Marine Birds in the Northwestern Barents Sea.
Arctic 51 (3); 243-252.
4
Munk P., Wright, P.J. and Pihl, N.J. (2002). Distribution of the Early Larval Stages of Cod, Plaice and
Lesser Sandeel across Haline Fronts in the North Sea. Estuarine, Coastal and Shelf Science 56.
Pingree RD & Griffiths DK (1978) Tidal fronts on the shelf seas around the British Isles, Journal of
Geophysical Research 83; 4615-4622.
Robinson, K.P., Tetley, M.J. and Mitchelson-Jacob, E.G. (2009). The distribution and habitat
preference of coastally-occurring minke whales (Balaenoptera acutorostrata) in the outer southern
Moray Firth, north east Scotland. Journal of Coastal Conservation 13(1): 39-48.
Scott B. E., Sharples J., Ross O. N., Wang J., Pierce G. J., Camphuysen C. J. (2010) Sub-surface
hotspots in shallow seas: fine-scale limited locations of top predator foraging habitat indicated by
tidal mixing and sub-surface chlorophyll. Mar Ecol Prog Ser 408: 207-226.
Sims, D.W. and Quayle, V.A. (1998). Selective foraging behaviour of basking sharks in a small-scale
front. Nature, 393, 460-464.
Tetley MJ, Mitchelson-Jacob EG, Robinson KP (2008) The summer distribution of coastal minke
whales (Balaenoptera acutorostrata) in the southern outer Moray Firth, NE Scotland, in relation to
co-occurring mesoscale oceanographic features. Remote Sensing of Environment 112; 34493454.
Webb, A., Harrison, N.M., Leaper, G.M., Steele, R.D., Tasker, M.L. and Pienkowski, M.W. (1990)
Seabird distribution west of Britain. Nature Conservancy Council, Peterborough.
Wright, P. J., Jensen, H., & Tuck, I. (2000). The influence of sediment type on the distribution of the
lesser sandeel, Ammodytes marinus. Journal of Sea Research, 44, 243-256.
5
SHELF DEEPS
Distribution of shelf deeps in Scottish waters
Around Scotland, shelf deeps are
recorded from the north Irish Sea (e.g.
Beauforts Dyke and the Mull of
Galloway Canyons), around the west
coast (e.g. Stanton and Malin Deeps,
Gulf of Corryvreckan, Inner Sound of
Raasay), to Shetland, and south
through the Fladen Deeps in the
northern North Sea to the Southern
Trench in the Moray Firth, the Buchan
Deep and the Devil’s Hole.
Map © Crown Copyright. UK Limits provided by UKHO Law of the Sea Division. All rights
reserved. Ordnance Survey Licence number SNH 100017908. 2011
General characteristics of shelf deeps
Description - Shelf deeps (or troughs) cover about 6,519 square kilometres of the UK’s
continental shelf. They are enclosed topographic depressions on the seabed, in most cases
created by glacial erosion during periods of lower sea level. The resulting deeps have
remained open and are significantly deeper than surrounding seabed. Several types of
deeps have been recognised in Scottish waters, including channels, troughs, valleys and
canyons.
Functional importance - There is limited published information on the functional role that
shelf deeps play within the wider Scottish marine ecosystem. However a study off the
Swedish coast by Rosenberg (1995) described the faunal abundance, biomass and diversity
as significantly higher at the trench floor (100 m) than on the shallow slope. In addition, a
predictive modelling study based on the Beauforts Dyke, located within the Irish Sea,
suggests that different areas of a deep can have variable numbers of species and diversity
(Callaway, 2011). In the case of the Beauforts Dyke this has been attributed to the
hydrodynamic processes occurring there with current speeds, turbulent kinetic energy and
mud content (as a proxy for organic content) having the greatest influence on the faunal
communities present (Callaway, 2011).
Functional importance of shelf deeps
Key supporting role - There is little information on the supporting role that deeps play in
Scottish shelf seas. Benthic community composition is highly likely to depend on the
substrate type present e.g. the base of the troughs where sediments accumulate are likely to
support deep sediment (mud, sand or gravel) communities including seapens, burrowing sea
anemones, sea cucumbers, starfish, brittlestars, and polychaetes. Hard substrates on the
walls or steeper slopes of the deep might support faunal communities, including cup and soft
corals, sponges, encrusting sea mats, and feather stars (Tyler-Walters et al., in prep.).
Deeps in the Sound of Canna, for example, are shown to support burrowed mud and sandy
muddy gravel communities. Benthic survey data (2009-2011) also identified several other
features, including the largest fan mussel bed in the UK located at depths below 100m, as
well as a horse mussel bed in the deepest part of the sound towards the southern end of the
shelf deep (Moore, 2011). Northern sea fan communities have been observed on the slope
leading into the shelf deep and dense aggregations of northern feather star are also
recorded in the area.
6
Functional links to top predators - A recent study on the foraging behaviour of minke
whales highlighted part of the south muck deep as a key area for this species (Anderwald et
al., 2011). This is thought to be due to the whales exploiting prey sources, which are
distributed in relation to parameters such as temperature and chlorophyll as well as the
influence of tides and season.
An area in the vicinity of the Southern Trench in the outer Moray Firth is recognised as an
important feeding area for cetaceans, however there is no evidence to suggest that the deep
itself provides enhanced feeding opportunities for cetaceans (Robinson et al., 2007). A
concentration of minke whale records also exist from an area of the central northern North
Sea which encompasses the Devil’s Hole deeps (Reid et al., 2003), but again it is not clear
whether there is any correlation between bathymetry and whale distribution.
There is, however, some evidence linking shelf deeps to seabird foraging in the North Sea
however this may not be a direct correlation. Approximately 19% of foraging trips by gannets
at the Bass Rock colony were in the vicinity of the Buchan Deep. The distribution of key
foraging areas has been linked to sites of enhanced productivity, such as fronts
(Camphuysen & Webb, 1999), which may be related to bathymetric features.
Speedie et al. (2009) identified a basking shark hotspot on a basalt plateau to the south-west
of Canna. However, there is no evidence to suggest that deeps are influencing this
distribution.
Connectivity - There have been few studies on the hydrographic characteristics of Scottish
shelf deeps. However it is likely that these large-scale features influence hydrographic
processes and may therefore play a role in connectivity.
In general, it is expected that deeps will exhibit weaker tidal and residual currents and
therefore may be relatively low-energy areas, with reduced levels of mixing near the seabed
and increased seasonal stratification. However, in some deep areas, energy may be
enhanced through internal mixing as a result of sloping bathymetry, or through generation of
density driven currents.
The Muck deep, for example, has been shown to have variable, but intensified near-bottom
currents, generated as a result of internal tide (SAMS, unpub.). The residual flow has been
described as westward towards land (SAMS, unpub.) and may contribute to density driven
cross-shelf circulation (e.g. Ellett & Edwards, 1983).
Issues and opportunities
Existing physical and biological mapping of shelf deeps is coarse in places. However,
analysis of multibeam and biological survey data is currently underway and will be used to
inform further assessment of search locations which contain this large-scale feature. For
example, recent survey data from locations including Shiant East Bank and the Southern
Trench is currently being processed and will help to better understand large-scale features in
these areas.
References
Anderwald P, Evans PGH, Gygax L, Rus Hoelzel A (2011) Role of feeding strategies in seabird-minke
whale associations. Mar Ecol Prog Ser 424:219-227
Callaway, A, Quinn, R, Brown, C, Service, M, Long, D and Benetti, S. (2011). The formation and
evolution of an isolated submarine valley in the North Channel, Irish Sea: an investigation of
Beaufort’s Dyke. Journal of Quaternary Science, 26 (4). pp. 362-373.
Callaway, A, Quinn, R, Brown, CJ, Service, M and Benetti, S. (2011). Trace metal contamination of
Beaufort’s Dyke, North Channel, Irish Sea: A legacy of ordnance disposal. Marine Pollution
Bulletin, 62. pp. 2345-2355
Camphuysen, K.C.J. & Webb, A. (1999) Multi-species feeding associations in North Sea seabirds:
jointly exploiting a patchy environment. Ardea 87:177-198.
7
Ellett, D., Edwards, A., 1983. Oceanography and inshore hydrography of the Inner Hebrides.
Proceedings of the Royal Society of Edinburgh, 83, 143-160.
Moore, C. G. and Roberts, J. M. (2011). An assessment of the conservation importance of species
and habitats identified during a series of recent research cruises around Scotland. Scottish Natural
Heritage Commissioned Report No. 446.
Reid, J.B., Evans, P.G.H., and Northridge, S.P. (2003). Atlas of Cetacean distribution in north-west
European waters. Joint Nature Conservation Committee. Peterborough, UK.
Robinson, K.P., Baumgartner, N., Eisfeld, S.M., Clark, N.M., Culloch, R.M., Haskins, G.M., Zapponi,
L., Whaley, A.R., Weare, J.S. and Tetley, M.J. (2007). The summer distribution and occurrence of
cetaceans in the coastal waters of the outer southern Moray Firth in northeast Scotland (UK). Lutra
50: 19-30
Rosenberg, R. (1995). Benthic marine fauna structured by hydrodynamic processes and food
availability. Netherlands Journal of Sea Research 34: 303-317.
Speedie, C.D., Johnson, L.A., and Will, M.J. (2009). Basing shark hotspots on the West Coast of
Scotland: Key sites, threats and implications for conservation of the species. SNH Commissioned
Report No.339.
Tyler-Walters, H., James, B. (eds.), Wilding, C., Durkin, O., Lacey, C., Philpott, E., Adams, L.,
Chaniotis, P.D., Wilkes, P.T.V., Seeley, R., Neilly, M., Dargie, J. and Crawford-Avis, O.T. (in prep.).
Descriptions of Scottish Priority Marine Features (PMFs) and Marine Protected Area (MPA) search
features. Scottish Natural Heritage Commissioned Report No. 406 (Project no. 25048).
8
SHELF BANKS AND MOUNDS
Distribution of shelf banks and mounds in Scotland’s seas
Shelf banks and mounds
occur off all Scottish coasts
e.g. the Shiant East Bank in
the Minch, Nun, Whiten Head
and Stormy Banks off the
north coast, Dutch and Forty
Mile Banks to the east of
Shetland, the Smith Bank in
the outer Moray Firth and the
Marr, Berwick, and Scalp
Bank together with the Wee
Bankie in the south-east in
the outer Firth of Forth
Map © Crown Copyright. UK Limits provided by UKHO Law of the Sea Division. All rights reserved.
Ordnance Survey Licence number SNH 100017908. 2011
General characteristics of shelf banks and mounds
Description - Shelf banks and mounds are formed by the action of strong currents on mobile
sediments (usually coarse sands and gravels) and rise with a slope greater than 2% from the
seafloor.
Functional significance - Aside from the shallower nature of bank features, which
potentially makes prey such as sandeels more readily available to predators, the passing of
tidal currents across their surface creates turbulence leading to the formation of internal
waves (Moum and Nash, 2000; Sharples, 2008). When the water column is stratified, this
allows relatively cooler, nutrient-rich deeper waters to mix with relatively warmer, nutrientdepleted waters serving to increase primary productivity and also to aggregate smaller prey
items. This can have profound effects on food availability for a range of species.
Functional significance of shelf banks and mounds
Key supporting role – Many shelf bank and mound features across Scotland support
populations of the lesser sandeel, Ammodytes marinus. Sandeels are a key prey item for
many top predators including gannets, kittiwakes, guillemots and species of cetacean such
as bottlenose dolphin and minke whale.
Functional links to top predators - A study by Scott et al. (2010) investigated the foraging
habitats of top predators in the Firth of Forth area by simultaneously collecting information on
hydrographic processes, habitat preferences and biodiversity. The study concluded that
small-scale hotspots were present where 50% of the animals recorded were actively foraging
in less than 5% of the study area. This foraging habitat was found to be linked to
hydrographic processes occurring, in part, as a result of the bank features in the Firth of
Forth area interacting with ocean currents. This leads to the generation of internal waves
causing enhanced levels of sub-surface chlorophyll as a result of enhanced vertical mixing.
Other studies have shown similar effects, with Lewis et al. (2004) suggesting that gannets
focus their foraging activity on areas that have characteristic bathymetric features and on
tidal mixing fronts that are probably associated with heightened levels of primary production.
9
Bank and mound features are thought in places to be important feeding grounds for
seabirds. Findings from the Centre of Ecology and Hydrology’s long-term research
programme based on the Isle of May, as well as other studies, demonstrate the critical
importance of banks in the outer Firth of Forth for foraging seabirds - particularly kittiwakes,
gannets and guillemots. The timing of availability and biomass of sandeels has been shown
to directly affect the breeding success of seabirds (Harris and Wanless, 1997; Rindorf et al.,
2000; Lewis et al., 2001; Frederiksen et al., 2005). For example, the breeding success of the
black-legged kittiwake (Rissa tridactyla) has been linked to the availability of sandeels (Daunt
et al., 2008).
Telemetry and modelling studies have shown some offshore bank features to be foraging
‘hot spots’ for marine mammals. Scott et al. (2010) showed this was linked to increased
levels of chlorophyll supporting key prey items as a result of internal waves. The edges of
bank features are also thought to be important in concentrating prey items and facilitating
herding behaviour in the feeding strategies of some cetacean species.
Connectivity – Bank and mound features have been shown to be important habitat areas for
sandeels and other fish species. Turbot Bank and other such banks and mounds in deeper
areas of Scotland’s seas that harbour sandeel populations may be important in supporting
the distribution of larvae across UK waters and further afield (Heath et al., 2012). Similarly,
Berwick Bank for example is thought to be an important spawning ground for plaice
(Pleuronectes platessa), the larvae of which may be important for repopulating exploited
stocks along the east coast of England (Lockwood and Lucassen, 1984).
References
Daunt, F., Wanless, S., Greenstreet, S.P.R., Jensen, H., Hamer, K.C., Harris, M,P. 2008. The impact
of the sandeel fishery on seabird food consumption, distribution and productivity in the
northwestern North Sea. Can. J. Fish. Aquat. Sci. 65: 362-381.
Frederiksen M, Wright PJ, Harris MP, Mavor RA, Heubeck M, Wanless S. 2005. Regional patterns of
kittiwake Rissa tridactyla breeding success are related to variability in sandeel recruitment. Mar
Ecol Prog Ser, 300, 201-211.
Harris MP, Wanless S (1990) The importance of the lesser sandeel Ammodytes marinus in the diet of
the shag Phalacrocorax aristotelis. Ornis Scand 22:375-882.
Harris MP, Wanless S (1997) Breeding success, diet and brood neglect in the Kittiwake (Rissa
tridactyla) over an 11-year period. ICES J Mar Sci 54:615-623.
Heath, M.R., Rasmussen, J., Bailey, M.C., Dunn, J., Fraser, J., Gallego, A., Hay, S.J., Inglis, M.,
Robinson, S. 2012. Larval mortality rates and population dynamics of Lesser Sandeel (Ammodytes
marinus) in the northwestern North Sea. Journal of Marine Systems 93: 47-57.
Ingham, S.N, Walshe, L., Johnston, D., Rogan, E. 2007. Habitat partitioning and the influence of
benthic topography and oceanopgrahy on the distribution of fin and minke whale in the Bay of
Fundy, Canada. Journal of the Marine Biological Association of the United Kingdom 87: 149-156.
Lewis S, Wanless S, Wright PJ, Harris MP, Bull J, Elston DA (2001) Diet and breeding performance of
black-legged kittiwakes Rissa tridactyla at a North Sea colony. Mar Ecol Prog Ser 221:277–284.
Lewis, S., Benvenuti, S., Daunt, F., Wanless, S., Dall’Antonia, L., Luschi, P., Elston, D.A., Hamer,
K.C., Sherratt, T.N. 2004. Partitioning of diving effort in foraging trips of northern gannets.
Canadian Journal of Zoology 82: 1910-1916.
Lockwood, S.L, and Lucassen, W. (1984). The recruitment of juvenile plaice (Plueronectes platessa)
to their parent spawning stock. J. Cons. Int. Explor. Mer 41: 268-275.
Moum, J.N., Nash, J.D. 2000. Topographically induced drag and mixing at a small bank on the
continental shelf. J. Phys Oceanography 30: 2049-2054.
Rindorf A, Wanless S, Harris MP (2000) Effects of sandeel availability on the reproductive output of
seabirds. Mar Ecol Prog Ser 202:241-252.
Scott, B.E., Sharples, J., Ross, O.N., Wang, J., Pierce, G.J., Camphuysen, C.J. 2010. Sub-surface
hotspots in shallow seas: fine-scale limited locations of top predator foraging habitat indicated by
tidal mixing and sub-surface chlorophyll. Marine Ecology Progress Series 408: 207-226.
10
Sharples, J. 2008. Potential impacts of the spring-neap tidal cycle on shelf sea primary production. J
Plankton Res 30: 183-197.
Wanless S, Harris MP, Greenstreet SPR. (1998). Summer sandeel consumption by seabirds breeding
in the Firth of Forth, south-east Scotland. ICES J Mar Sci 55:1141-1151.
11
CONTINENTAL SLOPE
Distribution of the continental slope in Scotland’s seas
The continental slope is a
geological feature which
divides the shelf sea and
deep ocean ecosystem. In
Scotland, the continental
slope comprises two distinct
regions; that north of the
Wyville-Thompson ridge (the
Faroe-Shetland Channel
slope) and that south of the
Wyville-Thomson ridge (the
Hebridean slope),
Map © Crown Copyright. UK Limits provided by UKHO Law of the Sea Division. All rights reserved.
Ordnance Survey Licence number SNH 100017908. 2011
General characteristics of the continental slope
Description - The continental slope is a geological feature which divides the shelf sea and
deep ocean ecosystem. It is largely regarded as a stratified environment, with environmental
factors such as light penetration, temperature, and current speed variable with depth (which
exends down to 3,000 m at its maximum) and slope gradient (which ranges from less than
0.1 degrees to 14 degrees). As such, the continental slope represents an area of ecological
and oceanographic significance where a wide range of species may be found.
Functional significance – In places the Scottish continental slope supports iceberg
ploughmark zones derived during glacial melt. This availability of hard substrata provides
ideal settlement locations for a range of benthic species such as cold-water corals and deep
sea sponges. Dependent on depth, there are also a wide range of other sediment types
present that support communities of deepwater species (Howell, 2010), These range from
cobbles and boulders in shallower areas of the slope to finer sands and muds in deeper
areas (Bett, 2000). On the Faroe-Shetland Channel slope for instance, the benthic
communities present are thought to be distinct to those from outside the channel (Henry &
Roberts, 2004) and as the only region in UK waters influenced by Arctic waters this also has
an influence on the distinctiveness of the types of species found here.
Hydrographic processes are also significant at the continental slope. In the Faroe-Shetland
Channel for example five different water masses converge in the relatively narrow channel.
Of particular importance is the boundary between the relatively cooler and relatively warmer
masses of water that occur between approximately 350 and 650 m known as the
intermediate waters masses. Here the presence of strong vertical gradients in temperature
permits internal wave formation leading to a zone of deep-water mixing and enhanced
current speeds (Sherwin, 1991). This has a strong influence on primary and secondary
productivity in the channel at these depths and the diversity of life found on the slope.
Functional significance of the continental slope
Key supporting role - Five different water masses converge in the Faroe-Shetland Channel
leading to the generation of a complex hydrographic regime. Cooler, dense water from the
Arctic basin flows southwest along the channel between depths of 800 and 1,200 m, whilst
warmer, Atlantic water flows over the top of it the northeast. Of particular note is the
boundary between the warmer and cooler waters, which occurs at a depth of between 350
12
and 650 m, known as the intermediate water masses. Here the presence of strong vertical
gradients in temperature permits internal wave formation leading to a zone of deep-water
mixing and enhanced current speeds (Sherwin, 1991).
This has profound effects on the ecology of the channel. Internal waves for instance are
important in the provision of food to benthic invertebrates such as cold-water corals
(Frederiken et al., 1992), and the diversity and abundance of species present has been
shown to be linked with the presence of the intermediate water masses. Benthic fauna for
instance show a diversity and abundance maximum at the intermediate water masses (Bett,
2000, Narayanaswamy et al., 2005, 2010). The same is true for fish assemblages in the
channel, with a diversity maximum at the transition zone between water masses (Bullough et
al., 1998; Gordon, 2001).
A diverse fish assemblage of over 200 species associated with the continental slope,
characterised by rapid shifts in species composition along a depth gradient. On the
Hebridean slope, dominant species include hake (Merluccius merluccius); greater argentine
(Argentina silus); bluemouth (Helicolenus dactylopterus); Baird’s smoothhead
(Alepocephalus bairdii); deep water sharks (for example Centrophorus squamosus,
Centroscymnus coleolepis); the Priority Marine Features: blue whiting (Micromesistius
poutassou), black scabbardfish (Aphanopus carbo), roundnose grenadier (Coryphaenoides
rupestris); and the MPA search feature blue ling (Molva dypterygia). Holt et al. (in prep)
report potential nursery grounds for several species of rabbit fish supported by the
Hebridean slope at depths ranging from 700 to 1000 m.
Functional links to top predators - The interaction between hydrographic processes and
the continental slope may enhance feeding conditions through the aggregation of principle
prey items (e.g. squid, herring, blue whiting and krill) for several species of cetacean,
including sperm whale, minke whale, killer whale, fin whale, long-finned pilot whale and
Atlantic white-sided dolphin (Macleod, 2004; Macleod et al., 2006, Stone, 1988; Swift et al.,
2002; Weir et al., 2001).
Connectivity – To the north of Scotland, the topographic nature of the Faroe-Shetland
Channel slope and wider channel is thought to be of functional significance as a migratory
pathway/corridor for several cetacean species. Of these, fin and sperm whales are the most
regular users of the route based on the data available. These cetacean species seem to use
the channel as a passage way to move through into colder, temperate waters to the north to
feed in the early summer months whilst some remain in the channel (e.g. Macleod et al.
2006) before travelling further south to lower latitudes to overwintering and breeding grounds
in the autumn and winter.
References
Bett, B.J. 2000. Benthic ecology of the Faeroe-Shetland Channel. Section 4.3.1 in Environmental
Surveys of the Seafloor of the UK Atlantic Margin, Atlantic Frontier Environmental Network [CDROM]. ISBN 09538399-0-7. Available from Geotek Limited, Daventry, UK.
Bett, B.J. 2001. UK Atlantic Margin Environmental Survey: introduction and overview of bathyal
benthic ecology. Journal of Continental Shelf Research 21, 917-956.
Bullough, L.W., Turrell, W.R., Buchan, P., Priede, I.G. 1998. Commercial deep water trawling at subzero temperatures: Observations from the Faroe-Shetland Channel. Fisheries Research 39. 33-41.
Frederiksen, R., Jensen, A., Westerberg, H. 1992. The distribution of the scleractinian coral Lophelia
pertusa around the Faeroe Islands and the relation to internal tidal mixing. Sarsia 77,157–171.
Gordon, J.D.M. 2001. Deep-water fisheries at the Atlantic Frontier. Continental Shelf Research 21,
987-1003.
Henry, L-A., Roberts, J.M. 2004. The biodiversity, characteristics and distinguishing features of deepwater epifaunal communities from the Wyville-Thomson Ridge, Darwin Mounds and Faeroes
Plateau. Report to the Atlantic Frontier Environmental Network.
Howell, K. 2010. A benthic classification system to aid the implementation of marine protected area
13
networks in the deep/high seas of the NE Atlantic. Biological Conservation 143, 1041-1056.
Macleod, K. 2004. Abundance of Atlantic white-sided dolphin (Lagenorhynchus acutus) during
summer off northwest Scotland. Journal of cetacean research and management 6 (1) 33-40
Macleod, K., Simmonds, M., Murray, L. 2006. Abundance of fin (Balaenoptera physalus) and sei
whales (B. Borealis) amid oil exploration and development off northwest Scotland. Journal of
cetacean research and management 8 (3) 247-254.
Narayanaswamy, B.E., Bett, B.J., Gage, J.D. 2005. Ecology of bathyal polychaete fauna at an Arctic–
Atlantic boundary (Faroe-Shetland Channel, North-east Atlantic). Marine Biological Research 1,
20-32.
Narayanaswamy, B.E., Bett, B.J., Hughes, D.J. 2010. Deep-water macrofaunal diversity in the FaroeShetland region (NE Atlantic): a margin subject to an unusual thermal regime. Marine Ecology 31,
237-246.
Sherwin, T.J., 1991. Evidence of a deep internal tide in the Faroe-Shetland Channel. In: Parker B.B.
(Ed), Tidal Hydrodynamics. John Wiley & Sons, New York: 469-488.
Stone, C.J. 1998. Cetacean observations during seismic surveys in 1997. JNCC Report 278. 57pp.
[Available from the Joint Nature Conservation Committee, Aberdeen]
Swift, R.J., Hastie, G.D., Barton, T.R., Clark, C.W., Tasker, M.L., and Thompson, P.M. 2002. Studying
the distribution and behaviour of cetaceans in the northeast Atlantic using passive acoustic
techniques. Report for the Atlantic Frontier Environmental Network.
Weir, C.R., Pollock, C., Cronin, C. and Taylor, S. 2001. Cetaceans of the Atlantic Frontier, north and
west of Scotland. Continental Shelf Research, 21: 1047-1071.
14
SEAMOUNTS
Distribution of seamounts in Scottish waters
There are three seamounts
in Scottish waters, all of
which fall within the Rockall
Trough to the far west of
Scotland. From top to
bottom, these seamounts
are Rosemary Bank, Anton
Dohrn and Hebrides
Terrace.
Map © Crown Copyright. UK Limits provided by UKHO Law of the Sea Division. All rights reserved.
Ordnance Survey Licence number SNH 100017908. 2011
General characteristics of seamounts
Description - Seamounts are undersea geological structures at least 100 m high that do not
reach the sea surface (Pitcher 2007). They are generally conical, elliptical or elongated in
shape, and usually of volcanic origin and/or associated with geological faults and magma
production hotspots (OSPAR 2010).
Functional significance - Oceanic currents in the Rockall Trough impinge on Scottish
seamounts creating dynamic hydrographic and sedimentary regimes (Howe and Humphery
1995; Howe et al. 2006; Inall and Sherwin 2006). For example, internal tides and seamounttrapped waves can be created by the interaction between oceanic currents and the
topography of seamounts (Stashchuk and Vlasenko, 2005). This can generate downwelling
and advection processes at seamounts that supply particulate organic matter to filter feeders
such as cold water corals (Davies et al., 2009). As a result, seamounts in Scottish waters
can often host diverse benthic communities which include cold-water corals, deep water
sponges and coral gardens. The three-dimensional structure of these communities serve to
increase species richness on seamounts, including crustaceans, cephalopods, echinoderms,
and anemones (FRS, 2008; Howell et al., 2010; ICES, 2011).
The hydrographic processes occurring on and around seamounts as a result of the
interaction between currents and seamount topography can also promote upwelling of
deeper, nutrient-rich waters that increase surface primary production (White et al. 2007).
They can also serve to retain prey items and key species around seamounts. For example,
downwelling eddies associated with Taylor Cones can promote the retention of larval fish
(Dower and Perry, 2001). These larvae may be important sources of food for other fish,
marine mammals, cephalopods and birds. Marine mammals are frequent visitors to Scottish
seamounts, where common and rare whales, dolphins and porpoises forage or visit en route
during their long migrations (Evans, 1997; Charif et al. 2001; Swift et al., 2002; Macleod et
al., 2003).
Functional significance of seamounts
Key supporting role – Seamounts in Scotland’s seas can support a biologically diverse
assemblage of cold-water coral reefs, coral gardens and deep-sea sponge communities
(Neat et al., 2008; Howell et al., 2010), which suggests that local productivity and/or
15
production are coupled with important retention mechanisms to support these communities.
The three-dimensional structure of these communities serve to increase species richness on
seamounts, including crustaceans, cephalopods, echinoderms, and anemones. The
biodiversity on seamounts attract rich fish communities that may use the seamount for
foraging, breeding and spawning. Rosemary Bank for example has been identified as an
important spawning ground for blue ling (Large et al., 2010), with over 40% of the population
engaged in spawning there (Large et al., 2004), and hosts important aggregations of blue
whiting (Neat et al., 2008). Diverse fish assemblages found in association with seamounts
make them important foraging areas for marine mammal species.
Functional links to top predators - The positive relationship between the steep slopes of
the seamounts and enhanced vertical mixing supports higher fish and cephalopod prey
densities. This in turn supports cetacean populations. The aggregations of blue whiting at
the Rosemary Bank seamount for example may be linked to the occurrence of large schools
of marine mammals at Rosemary Bank (Weir et al., 2001), where they may topographically
‘focus’ prey across small areas thereby minimising energy expenditure (Bailey and
Thompson, 2010).
Connectivity - The hydrography of Scottish seamounts could affect larval dispersion and
species connectivity over wide spatial scales. The presence of eddies near Rosemary Bank
for example brings Norwegian Sea Deep Water (Ellett et al., 1983) that could collide with
seamounts and advect particles further downstream. Indeed, seamount productivity or
production is more frequently derived from upstream sources of nutrients, organic matter,
phytoplankton, zooplankton, larvae and even fish that get advected to the seamount (Genin
and Dower, 2007). This suggests seamount protection could play an important role in the
wider conservation of Scotland’s seas and further afield.
Many marine mammals are long-ranging species, travelling hundreds to thousands of
kilometres along traditional migration routes. Along the way, cetaceans are known to
frequent seamounts as part of their life histories. For the cetaceans found in the vicinity of
Scottish seamounts, the migration route through the Rockall Trough to their over-wintering
grounds in the Faroe-Shetland Channel is one of the most important to their life histories
(Evans, 1997; Swift et al., 2002; Macleod et al., 2003).
References
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movements of bottlenose dolphins. Marine Ecology Progress Series, 418. 223-233.
Charif, R.A., Clapham, P.J., and Clark, C.W. 2001. Acoustic detections of singing humpback whales
in deep waters off the British Isles. Marine Mammal Science, 17. 751-768.
Clarke, M. 2007. Seamounts and cephalopods. In: Seamounts: Ecology, Fisheries and Conservation.
Pitcher, T.J., Morato, T., Hart, P.J.B., Clark, M.R., Haggan, N., and Santos, R.S. (Eds). Blackwell
Publishing, Oxford. 207-229.
Davies, A.J., Duineveld, G., Lavaleye, M., Bergman, M.J., van Haren, H., and Roberts, J.M. 2009.
Downwelling and deep-water bottom currents as food supply mechanisms to the coldwater
Lophelia pertusa (Scleractinia) at the Mingulay reef complex. Limnology and Oceanography, 54.
620–629.
DEFRA. 2007. Report of the results from UK observer trips in the westerly gillnet fishery for anglerfish.
Department for Environment, Food and Rural Affairs, April 2007.
Dower, J.D., and Perry, R.I. 2001. High abundance of larval rockfish over Cobb seamount, an isolated
seamount in the northeast Pacific. Fisheries Oceanography, 10. 286-274.
Ellett, D.J., Kruseman, P., Prangsma G.J., Pollard, R.T., Van Aken, H.M., Edwards, A., Dooley, H.D.,
and Gould, W.J. 1983. Water masses and mesoscale circulation of North Rockall Trough waters
during JASIN 1978. Philosophical Transations of the Royal Society of London A, 308. 213-252.
Evans, P.G.H. 1997. Ecology of sperm whales (Physeter macrocephalus) in the Eastern North
Atlantic, with special reference to sightings and strandings records from the British Isles. Bulletin
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de l'Institut Royal des Sciences Naturelles de Belgique, Biologie, 67 (Supplement). 37-46.
FRS. 2008. FRS Marine Laboratory FRV Scotia Cruise Report. 2–23 September 2008. Cruise 1108S.
Flammang, B.E., Ebert, D.A., and Cailliet, G.M. 2011. Intraspecific and interspecific spatial distribution
of three eastern North Pacific catshark species and their egg cases (Chondrichthyes:
Scyliorhinidae). Breviora (Museum of Comparative Zoology), 525. 1-18.
Genin, A., and Dower, J.F. 2007. Seamount plankton dynamics. In: Seamounts: Ecology, Fisheries
and Conservation. Pitcher, T.J., Morato, T., Hart, P.J.B., Clark, M.R., Haggan, N., and Santos,
R.S. (Eds). Blackwell Publishing, Oxford. 85–100.
Howe, J.A., and Humphery, J.D. 1995. Photographic evidence for slope-current activity, Hebrides
Slope, NE Atlantic Ocean. Scottish Journal of Geology, 31. 107-115.
Howe, J.A., Stoker, M.A., Masson, D.G., Pudsey, C.J., Morris, P., Larter, R.D., and Bulat, J. 2006.
Seabed morphology and the bottom-current pathways around Rosemary Bank seamount, northern
Rockall Trough, North Atlantic. Marine and Petroleum Geology, 23. 165-181.
Howell, K.L, Davies, J.S., and Narayanaswamy, B.E. 2010. Identifying deep-sea megafaunal
epibenthic assemblages for use in habitat mapping and marine protected area network design.
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2004. Fisheries Management Group, CEFAS, Lowestoft. 7 June 2004.
Large, P.A., Diez, G., Drewery, J., Laurans, M., Pilling, G.M., Reid, D.G., Reinert, J., South, A.B., and
Vinnichenko, V.I. 2010. Spatial and temporal distribution of spawning aggregations of blue ling
(Molva dypterygia) west and northwest of the British Isles. ICES Journal of Marine Science, 67.
494-501.
Macleod, K., Simmonds, M.P., and Murray, E. 2003. Summer distributions and relative abundance of
cetacean populations off north-west Scotland. Journal of the Marine Biological Association of the
UK, 83. 1187-1192.
Morato, T., Varkey, D.A., Damaso, C., Machete, M., Santos, M., Prieto, R., Santos, R.S., and Pitcher,
T.J. 2008. Evidence of a seamount effect on aggregating visitors. Marine Ecology Progress Series,
357. 23–32.
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Pitcher, T.J., Morato, T., Hart, P.J.B., Clark, M., Haggan, N. and Santos, R. (eds). 2007. Seamounts:
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Stashchuk, N., and Vlasenko, V. 2005. Topographic generation of internal waves by nonlinear
superposition of tidal harmonics. Deep-Sea Research I, 52. 605-620.
Swift, R.J., Hastie, G.D., Barton, T.R., Clark, C.W., Tasker, M.L., and Thompson, P.M. 2002. Studying
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techniques. Report for the Atlantic Frontier Environmental Network.
Weir, C.R., Pollock, C., Cronin, C., and Taylor, S. 2001. Cetaceans of the Atlantic Frontier, north and
west of Scotland. Continental Shelf Research, 21. 1047-1071.
White, M., Bashmachnikov, I., Arístegui, J., and Martins, A. 2007. Physical processes and seamount
productivity. In: Seamounts: Ecology, Fisheries and Conservation. Pitcher, T.J., Morato, T., Hart,
P.J.B., Clark, M.R., Haggan, N., and Santos, R.S. (Eds). Blackwell Publishing, Oxford. 65-84.
17