- Methods -

Oceaneering Millennium ROV collecting sediment samples at the seabed at over 1700 m depth off Tanzania

Survey methods

The nature of work carried out through the SERPENT Project, taking place on a working

drillship, means it is opportunistic. A selection of techniques is required to maximize

the scientific data that can be collected when the opportunities arise. The techniques

vary depending on the availability of ROVs, the facilities on the rig or drillship and the

weather conditions at the time of the visits. Fortunately the weather off Tanzania was

generally very good. Only a few days lost to poor conditions across all the offshore visits.

A technique used on all SERPENT offshore visits is to document the appearance of the

seabed and the abundance of the megafauna (larger animals that can be seen in video)

using video transects. To do this the operator moves the ROV slowly in a straight line

at consistent height above the bottom with the camera viewing the seabed. The video

feed is recorded to disc. Observations are noted at the time but the real analysis is completed

when the video footage is reviewed on return to the laboratory. This consistent

methodology means that each section of video transect is considered a sample. Multiple

samples are collected at each site visited. These can then be compared with others taken

at a different time or location.

The video transects are of most value if there is sufficient detail about the species encountered.

Therefore, in separate surveys the ROV operators are asked to stop at every

species or feature of interest and a selection of stills and video footage is taken from all

possible angles. It is these images that make up the majority of this guide.


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