Minerals Report - International Seabed Authority

Levene’s test could also be used to examine whether a particular habitat is
being actively selected by a species, which allows impact to be
investigated.
Factor analysis was used to reveal the way in which species are
distributed along composite environmental axes, and were supplemented
by using a variety of other statistical techniques. Comparison of the
density of demersal nekton between different sites is complicated by the
dissimilar distribution of samples from video transects and the fact that
distinct associations with substrata do occur. It was possible to partially
resolve these problems by examining substrata by comparison on the
following basis:
� Disturbed vs. Undisturbed, soft vs. Mixed vs. Hard;
� Disturbed vs. Undisturbed, Assorted Major Substrata
In order to try to understand behaviour of the demersal fishes in
their natural environment, the activity of each demersal fish was assigned
to one of the following behaviours [28]:
� Hovering off substratum
� Positioned on the substratum
� Swimming in the water column
� Positioned in a crevice or under an overhang
� Occupying a shelter hole
� Buried (fully or partially) in the substratum.
Observations on the substratum on which fish were seen were also
recorded to try to correlate behaviours to the physical environment. Hence
the activity of each of the dominant species of demersal fish was analysed.
Perhaps surprisingly for people who have not experienced diving in
submersibles, no fish species has been found to flee the craft until it is next
to them [27,28]. However, seals have been known to quickly realise the
opportunity of enhanced hunting during dives off Namaqualand on the
west coast of South Africa. Not only is this a hassle for the fish, but also
for the Jago observers who disappear in clouds of suspended silt due to
the frenzy of external activity. A notable, if unusual observation is then
that seals are pretty tricky to shake off in a slow moving submersible!
Gibbons et al [28] recorded counts of all sessile macro fauna for a
minimum of 10 “video samples” for each dive from a habitat of uniform
INTERNATIONAL SEABED AUTHORITY 638