Minerals Report - International Seabed Authority

The video equipment used was upgraded to a digital system and
the intensity of the red laser dots for measurement was increased so that
they could be readily detected on video footage. As with the previous
analysis, video collected when the submersible was stationary, or when it
moved off the bottom, or in poor visibility was ignored. Video acquisition
was not continuous throughout dives, but at the discretion of the observer.
Out of a total of 51 dives, 36 dives were conducted off Namibia.
The initial analysis of video data demonstrated that application of
the technique is non-trivial! The analytical method was improved
significantly by [28]. The entire videotape for each dive was inspected, but
only samples were examined in detail and analysed. Each sample had to
meet the following criteria:
� Recorded along linear sections of the cruise track;
� The submersible was moving at a slow but constant speed;
� The visibility was good.
The samples were of multiples of 31 seconds duration and the
environment in each sample was categorised by major (>50%) and minor
(>20%) substratum type, and all sedentary biological features were
recorded as present or absent. All nekton were identified and counted, and
these were subsequently converted into densities (m²) with knowledge of
horizontal distance traversed and the width of the video frame. Following
quality control, a total of 476 samples were obtained from the complete
collection of videotapes. These samples covered an area of 12 087 m², and a
total of 1 455 transects (between the red lasers) were obtained from the
video coverage to analyse the epifauna and infauna communities of the
benthos.
More advanced methodologies were used to determine the
associations between nekton and features of the physical and biological
environment [34,32]. This allowed the species mean to be determined,
which reflects preferences for individual species for different variables.
From a correlation matrix for all species’ means for the measured
environmental variables, patterns of habitat usage can be examined. Factor
analysis on the matrix can then be used to resolve patterns of
interrelationships amongst the variables with the result that trends in
habitat use can be determined statistically. It is also possible to compare
habitat use between different species. It was found that the application of
INTERNATIONAL SEABED AUTHORITY 637