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

Plate 2
ASML drop camera and frame and hand deployment over the side of survey
vessel Lophelia within the Sound of Canna
At each station, the video camera was lowered to the seabed. The boat and camera were
allowed to drift until the biologist controlling the recording felt there was enough footage to
categorise the benthic habitats present. At some stations, particularly along the coast of
Rum, the camera drifted towards the shore across several depth zones. GPS waypoints
were taken on these tows to mark biotope boundaries or particular features of interest.
Whilst the video tows were underway, notes were made by one of the biologists detailing the
species visible and the seabed substrata displayed on the television screen. This initial field
assessment identified any MPA search features or PMFs and their position was noted.
Subsequent post-fieldwork analysis of the tapes involved reviewing the footage more
thoroughly to identify as many species as possible and to produce a more detailed
description of the seabed. In some cases, the low level of information retrievable from the
tapes meant that the site could fit into any one of several biotopes. In these cases the
biotope was assigned to a higher level in the classification. This was particularly pertinent at
shallow sediment stations supporting algal communities but with few conspicuous animals
(such biotopes are notoriously difficult to identify from video footage).
It proved impossible to survey the cliffs using the drop-down video and so SNH’s mini ROV
(VideoRay Pro400SE) was deployed in an effort to look at the vertical cliff walls beyond
diving depths. However, the inadequate charting of the area combined with adverse
weather conditions meant that the boat was unable to anchor in the shallow water above the
cliffs and no additional footage was obtained.
The results of the video work were entered into an Excel spreadsheet and Marine Recorder.
No statistical analysis of the video results was deemed appropriate.
2.3.2 Deep water video survey
The deep water video survey was undertaken in conjunction with the grab sampling (covered
in Section 2.4). As in the preceding shallow water work, sampling locations were selected to
provide an overview of the full range of habitat types likely to be present throughout the
sound but with significantly greater sampling intensity in areas of known or anticipated fan
mussel occurrence. Unsuccessful attempts were made during the deep water video work to
sample the deeper vertical bedrock cliff areas using the SNH/MSS Seaeye Falcon ROV.
Sixty deep water stations were sampled (code A) and a further seven shallower locations,
identified on the basis of the earlier video work and follow-up diver sampling (see
Section 2.5) were assessed specifically looking for maerl (code M). The video runs are
illustrated on Figure 8.
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