Marine biological survey to establish the distribution and status of ...

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Rum has a far more complex structure, with the jagged gabbro of the Rum Cuillins being the remains of another volcano. The rounded granite of the headland at A’Bhrideanach at the south-west entrance to the sound is also a product of this volcanic activity. The north-west coast bordering the Sound of Canna consists largely of Torridonian sandstone with a small area of more recent sedimentary rock. Glaciation and the subsequent rise of the land led to the formation of raised beaches which are evident around both Rum and Canna. The raised beach at Harris on the south-west coast of Rum (to the south of Figure 1 coverage) is 30 m above the present-day tidemark with a similar but smaller beach fragment at Kilmory Bay. Six metres above high tide level at Guirdil and Kilmory there is also a second set of postglacial raised beaches, formed around 6,000 years ago (Goodenough and Bradwell, 2004). The Sound of Canna is a steep-sided channel over-deepened by glaciation. It is just over 3 km wide at its narrowest point and reaches a maximum depth of 275 m, shallowing to about 90 m at the south-western end. A boulder slope along the Rum coast drops to a gravel shelf at about 20 to 25 m which extends along the whole north-west coast of the island. Below this is a steep sediment slope to the floor of the channel. There is a sandy beach at the head of Kilmory Bay and the clean sands extend into the subtidal. On the western side of the channel, a rock wall along the south and east coasts of Sanday drops vertically from about 15 m to over 60 m depth where a steep boulder and sediment slope continues to the channel floor (Figure 2). In shallower water along this coast there is a rock and boulder shelf with small skerries and patches of sand in the most sheltered parts. On the eastern end of Sanday the underwater cliffs extend eastwards, as a reef, and there is a short north facing wall known to local divers. Figure 2 A diver’s interpretation of the Sanday cliffs (Davidson, 1982) The entrance to Canna Harbour is sheltered from the prevailing winds and supports areas of finer muddy sediments. The skerry of Sgeir a’Phuirt has a sheltered steep north wall dropping to about 30 m depth, with a shallower and more gradually sloping southern side which drops into a sheltered sediment channel. On the east coast of Canna there is very little inshore rock; a sediment slope, very steep in places, comes almost to the shoreline. However, on the north-east corner of the island at An t-Each there is a short stretch of steep, north facing underwater rock from about 20 m depth, outcropping from a sediment slope. 3
The floor of the sound supports a range of sedimentary substrates, from sand to mud, with large amounts of shell debris common. Boulder piles, which are probably glacial debris, either morainic or dropstones shed by decaying icebergs, are scattered throughout. There are also areas of uncharted bedrock along the edges of the deep central channel. 1.3.2 Previous marine biological sampling in the Sound of Canna There has been relatively little formal survey work carried out in the Sound of Canna (see Table 1 below and Figure 3 overleaf). A diving team from the Nature Conservancy Council (NCC - the predecessor of SNH and its sister conservation agencies) visited Rum in 1980 and carried out several dives along both sides of the sound. The majority of their diving was shallower than 30 m and, as the northern sea fans in the area seem to be found below this depth, this species was not recorded. Table 1 Marine biological surveys undertaken within the Sound of Canna Year Commissioning organisation Survey type Sites MPA search features / *PMFs recorded Reference 1980 1988 Nature Conservancy Council / Underwater Conservation Society Nature Conservancy Council Diving survey, Phase 2 style Diving survey, Seasearch 10 European spiny lobster Palinurus elephas Burrowed mud (CFiMu.MegMax) 3 none Dipper, 1981 MacKinnon, 1988 Seagrass beds (SS.SMp.SSgr.Zmar) 1993 Scottish Natural Heritage ROV 4 Burrowed mud (CFiMu.MegMax & CFiMu.SpnMeg) Kelp and seaweed communities on sublittoral sediment (KSwSS.LsacCho & KSwSS.LsacR.Sa) Burrowing sea anemone Arachnanthus sarsi Scottish Natural Heritage, 1993 2004, 2006, 2007 Marine Conservation Society Diving survey, Seasearch 7 Northern sea fan and sponge communities (CR.MCR.EcCr.CarSwi); *White cluster anemone Parazoanthus anguicomus Seasearch, 2004. Individual recording forms only in 2006 & 2007 2009 Marine Scotland Science Drop video 3 transects Fan mussel Atrina fragilis aggregations Marine Science Scotland, 2009 The 1980 survey recorded jewel anemones, hydroids, sponges and a turf of bryozoans from the underwater cliffs. The cotton spinner sea cucumber Holothuria forskali and the European spiny lobster Palinurus elephas, an MPA search feature, were both reported. Of particular interest was the presence of the sea cucumber Parastichopus tremulus, an unusual deep water species, on Sgeir a’Phuirt. This species does not appear to have been recorded by more recent surveys. NCC divers surveyed kelp forest and gravel shelf communities along the Rum shore and did not consider the area to be of conservation interest (Dipper, 1981). Short diving surveys were also conducted by mixed teams of marine biologists and recreational divers in 1988 (MacKinnon, 1988) and 2004, 2006 and 2007 (Seasearch). These surveys included dives on the Sanday cliffs, with the 2004 and 2007 studies recording northern sea fan communities below the lighthouse. 4
Page 1 and 2: Scottish Natural Heritage Commissio
Page 4 and 5: COMMISSIONED REPORT Summary Marine
Page 6 and 7: Contents Page no. 1 Introduction ..
Page 8 and 9: Page no. Figure 28 Basking shark ho
Page 10 and 11: 1 INTRODUCTION 1.1 Background The S
Page 14 and 15: In 1993 an SNH team conducted remot
Page 16 and 17: Richardson et al. (2004) showed tha
Page 18 and 19: 2 METHODS 2.1 Sampling strategy The
Page 20 and 21: Figure 6 Shallow water video statio
Page 22 and 23: Figure 8 Video stations surveyed in
Page 24 and 25: Each discrete grab sample was empti
Page 26 and 27: Following the survey, the infauna w
Page 28 and 29: Table 2 Biotopes identified in the
Page 30 and 31: Figure 11 2010 survey coverage off
Page 32 and 33: Circalittoral sandy mud (SS.SMu.CSa
Page 34 and 35: Description The distribution of the
Page 36 and 37: Figure 16 Division of the megafauna
Page 38 and 39: Some L. saccharina forest (IR.LIR.K
Page 40 and 41: Rhodophyllis werneri and Scinaia in
Page 42 and 43: Plate 8 A northern sea fan Swiftia
Page 44 and 45: Zostera marina/angustifolia beds on
Page 46 and 47: This is consistent with infaunal co
Page 48 and 49: the fan mussels ranged from an esti
Page 50 and 51: Plate 13 A small basking shark in C
Page 52 and 53: Distribution Depth range: 72 - 21
Page 54 and 55: Figure 31 Other species of interest
Page 56 and 57: coverage predictive biotope distrib
Page 58 and 59: 4 DISCUSSION This section presents
Page 60 and 61: Table 4 Summary of the assessment o
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The burrowed mud supported langoust
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in areas where it is protected from
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Table 6 Summary of a preliminary as
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5.2 Future data review and biologic
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Ingle, R.W. (1996). Shallow-water c
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Appendix 1 Drop-down video and dive
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Date Station Time Latitude Longitud
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Table A1.2 Summary notes (biologica
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Tow Id no Tow Data point Date Tape
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Tow Id no Tow Data point Date A123
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Table A1.3 Summary of sampling unde
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Site No. Date Habitat Id (Site No:H
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Species MCS Code D D 1 _ 2 D D 1 _
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Species MCS Code Suberites ficus C2
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Species MCS Code Cryptopleura ramos
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Species MCS Code Scrupocellaria Y83
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Table A1.6 Species recorded (matrix
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Species MCS Code A 1 2 _ 1 A 1 2 _
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Table A1.7 Species recorded (matrix
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Species MCS Code Dive 1.1 Dive 2.1
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Table A2.1 Positional and depth inf
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Table A2.3 List of taxa identified
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Taxa MCS Code G 01 G 02 G 03 G 04 G
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Taxa MCS Code G 01 G 02 G 03 Diasty
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Taxa MCS Code G 01 Ascidiella sp. Z
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Figure A2.1 Bray-Curtis similarity
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Appendix 3 Macrofaunal and sediment
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Table A3.3 Results of univariate an
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Appendix 4 Photo and video logs - 2
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File Name Subject Site Name Island
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Table A4.2 Drop-down video log, 201
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File Name File size Folder Site No
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File Name File size Folder Site No
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