Site selection and carrying capacity in Mediterranean ... - FAO Sipam

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In the following, we provide indicators for monitoring the ecological effects of aquaculture on
sediments and water quality (see also Table 3). We describe various means to monitor change
at aquaculture sites and proceed from to describe change in sediment quality, including both
physico-chemical and biological aspects. This is followed by a description of changes in
water quality and how these may be monitored. All of the above will be discussed with
respect to the level of expertise and time needed and requirements for special instrumentation
and facilities. Cost per analysis will vary greatly from country to country and is linked to
availability of suitable analytical equipment and experience in performing the analyses.
3.1 Monitoring change at aquaculture sites
Visual, photographic and video surveys
Surveys using photography, video or direct observation may be conducted at sites where
visibility and conditions permit. This approach is especially suitable for many parts of the
Mediterranean where light penetrates through the water column to great depths and the high
water transparency and visibility allow good quality underwater photography and
videography to be made. The length, number and locations of transects are site-specific and
related to the monitoring strategy to be adopted. For intertidal shellfish farms, photographs of
the lease area at low tide are normally sufficient. However, most aquaculture sites in the
Mediterranean are sub tidal and visual, videographic or photographic surveys must be done
by means of diving or using remotely operated vehicles (ROVs). The video survey approach
is relatively inexpensive and readily provides qualitative or semi-quantitative information on
benthic impact and sediment quality, and can provide information on much larger areas than
other methods. This form of monitoring can identify both areas of organic enrichment and
inorganic debris (e.g. bivalve shells and farm litter) beneath the farm. Moreover, video
surveys may indicate the spread of fish feed from the cage area, hence also serving for
management and husbandry, in addition to ecological objectives. Whereas it is relatively easy
to generate large volumes of underwater photography and video footage, this must be
followed by time consuming analysis of the images or videos to determine sediment status
along the transects and the extent of the impacted seedbed area. Another option is to use
diver-based observations to determine conditions around aquaculture facilities. This approach
relies on the assumption that the divers are familiar with a suite of features that characterize
healthy and unhealthy conditions in the benthic and pelagic environment around a farm and
are able to record these along transects during underwater surveys. This approach has been
used below fish farms in Maine (Heinig 2000) and in the Red Sea (Angel et al. 1998). The
advantage of on-site direct observations using diving is that there is no need to carry out postdive
viewing and assessment of video recordings (e.g. as has been done in Tasmania; see
Crawford et al. 2001) and the data may be analyzed by techniques such as fuzzy logic (Angel
et al. 1998). If the seabed at aquaculture sites lies in very deep waters (>30m), it may not be
possible to use SCUBA divers efficiently for visual/video/photography surveys. Another
option is to use ROVs equipped with underwater cameras and video cameras.
Time required: depending on factors such as visibility and site characteristics; between 0.5 - 1
day per transect.
Necessary equipment and infrastructure: submersible video or digital photography camera with
appropriate underwater lighting, electronic equipment for post-collection viewing.
Level of expertise required: SCUBA divers experienced in laying transect lines, with training in
underwater videography and/or photography; high-resolution monitor for viewing and analysis
of underwater footage.