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

The video survey was carried out in depths of up to 275 m and this required a robust camera
system heavy enough to reach the seabed without streaming too far behind the boat. Due to
the time required to deploy the system in deep water, the camera was left down for much
longer than the shallow water system, particularly when trying to ascertain the extent of the
fan mussel bed. The longest video sample was approximately 42 minutes. The camera was
controlled from the surface and it was generally possible to keep the frame just above the
seabed enabling a biologist to record contemporaneous notes to accompany the footage.
The video camera was not a digital system and the quality of the footage was lower than that
obtained using the shallow water equipment.
2.4 Grab sampling
Towards the end of the deep video work, a full day (25 th September) was dedicated to the
collection of 23 infaunal samples using a Day Grab (0.1m 2 volume). The distribution of the
grab stations is illustrated in Figure 9. Sample locations were selected on the basis of the
preceding video survey, ensuring good coverage across the sound and targeting specific
biotopes of interest. Two samples were taken at Guridil in an effort to sample the maerl
observed there. The first sample (G23) was too deep so the boat moved in shallower for a
second grab (G22).
Figure 9
Distribution of grab sampling stations within the Sound of Canna
(note - there was no Station G16)
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derived in part from material obtained from the UK Hydrographic Office with the permission of the Controller of Her Majesty's Stationery Office
and UK Hydrographic Office (www.ukho.gov.uk). NOT TO BE USED FOR NAVIGATION
The position of each grab station was recorded by GPS and each infaunal sample was
processed on board. Only full grab samples were retained and no replicates were taken. A
subsample (~200 g) was taken from the surface of each grab for sediment grain size
distribution analyses and organic matter content determination for correlation of the
sediment characteristics with the infaunal community.
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