Sea bed video, grab, contaminants and trawl sampling coordinates and any associated field observations are provided in Appendices D‐G.
Sample positioning including grabs, trawls and sea bed video was achieved using a Hemisphere Crescent V100 DGPS which has a stated horizontal accuracy of <0.6m (95% confidence). Navigation and position recording was achieved using Trimble’s HYDROpro ™software version 2.30.844.
31.
Two trawl sites, one sediment contaminants site and one Hamon grab site were micro sited in the field from their target locations. Site T09 and Site T11 were relocated to avoid potential Annex 1 Sabellaria spinulosa biogenic reef. Contaminants site 56 was relocated to site 39, due to the presence of coarse substrate not suitable for contaminants sampling. Hamon grab Site 40 was moved approximately 200m east due to the presence of potential Annex 1 S. spinulosa biogenic reef.
1.3 Sea Bed Video 32.
At each sample location, the sea bed was initially surveyed using a drop down digital video and stills camera mounted within a frame and towed astern of the vessel over the sea bed surface, at a speed of approximately 0.5knots. The duration of the video and camera deployment was sufficient to ensure that nature and heterogeneity of local sea bed habitats and characterising communities were captured; this was generally a minimum of ten minutes. Where visibility was poor the freshwater box system ELViS was deployed to gather video footage and photographic stills.
33. 34.
All video data were geo‐referenced. Observer records were collated throughout each deployment including substrate type and conspicuous epifauna.
During each deployment of the video a minimum of five photographs were collected. These were subsequently used to illustrate the different habitat encountered during each video deployment and to confirm the identity of species noted in the field. Representative sea bed photographs for each video deployment are presented in Appendix H.
35.
Notably, underwater visibility during the benthic survey was highly variable, dependent on locality. Many of the sites were subject to more than one attempt, on different states of the tide, in order to obtain video footage and stills images sufficient for the purposes of analysis. Within the inshore sites, highly turbid conditions were
Benthic Characterisation Report November 2013
East Anglia THREE and FOUR Offshore Cable Corridor
