Statement |
New multibeam echosounder (MBES) bathymetry and backscatter data were acquired during a survey by Cefas, for the purposes of completing the acoustic data coverage of the rMCZ area in the north-western part of the rMCZ. The survey was carried out between the 21st and 23rd of January 2013 on RV Cefas Endeavour using the Kongsberg EM2040 system, operated at 300 kHz (Ware, 2013). The remainder of the area is covered by MCA CHP data collected by contractor Fugro OSAE between 20th April 2009 and 31st March 2011 using range of vessels (Meridian, Jetstream, Victor Hensen and Fugro Gauss) and multibeam systems (EM710, EM3002D, Reson 7125). Acoustic survey imagery is presented in Appendix 2.
The inshore part of the area was groundtruthed by an Environment Agency survey, in order to characterise the surface sediment and benthic communities present. This survey was conducted by the Briggs Marine survey vessel Severn Guardian between 18th February and 2nd May 2013 (SNGN 03/13; Godsell, 2013). Twenty-one samples from this survey were analysed for particle size. In addition, 240 images from Drop video camera equipment were classified for BSH (Figure 2). Drop video camera equipment was deployed in accordance with the MESH ÔÇÿrecommended operating guidelines (ROG) for underwater video and photographic imaging techniquesÔÇÖ (Coggan et al., 2007). The SES Seabug camera system was deployed from the stern of the survey vessel. Real time navigation data acquisition and manual position fixing when the gear contacted the seabed was captured via Trimble┬« HYDROproÔäó software and logged by the survey officer. The mid-point of the vesselÔÇÖs stern gantry was used as the default offset for position fixing. Video files and digital still images were transmitted via the sea cable to be captured and saved directly to a laptop in the survey cabin. The video footage was annotated with time and position using a GPS (SIMRAD MX512 DGPS) referenced video overlay (uncorrected position data). Images of the seabed were captured approximately every 10 to 15 metres over a distance of >150 metres. Extra photographs were taken in heterogeneous areas of BSH and if particular habitat/species FOCI were observed. The camera deployment was extended if a BSH habitat boundary was detected for estimating spatial extent. In addition to acoustic data, Cefas survey CEND01/13Y collected eight Hamon grab samples which were analysed for particle size information. Samples were classified into both Folk and EUNIS BSH classes.
Drop-camera deployments lasted a minimum of 10 minutes, with the vessel executing a controlled drift at ~0.5 knots (~0.25 m s -1 ) across a 50 m ÔÇÿbullringÔÇÖ centred on the sampling station. Still images were captured at regular one minute intervals and opportunistically if specific features of interest were encountered. The camera was deployed from the side gantry, amidships, with the height of the camera off the seabed being controlled by a winch operator with sight of the video monitor.
Video and still images were analysed by APEM Ltd following an established protocol developed by Cefas (Coggan et al., 2007; JNCC, in prep.; see Annex 5). A broadscale habitat type, habitat FOCI (if applicable) and biotope was then assigned to each still according to EUNIS Level 3. From the two surveys, a total of 849 images were assessed with 44% being assigned to ÔÇÿA5.1 Subtidal coarse sedimentÔÇÖ, 29% to ÔÇÿA4.2 Moderate energy circalittoral rockÔÇÖ, 15% to ÔÇÿA4.1 High energy circalittoral rockÔÇÖ, 9% to ÔÇÿA5.2 Subtidal sandÔÇÖ and 3% to ÔÇÿA3.1 High energy infralittoral rockÔÇÖ. Twenty nine PSA samples were collected in total. Eleven were classified as ÔÇÿA5.1 Subtidal coarse sedimentÔÇÖ, 17 as ÔÇÿA5.2 Subtidal sandÔÇÖ and one as ÔÇÿA5.4 Subtidal mixed sedimentsÔÇÖ.
All new habitat maps and their derivatives have been based on a WGS84 datum. A new habitat map for the site was produced by analysing and interpreting the available acoustic data (as detailed above) and the ground truth data collected by the dedicated surveys of this site. The process is a combination of two approaches, autoclassification (image analysis) and expert interpretation, as described below. The routine for auto-classification is flexible and dependent on site-specific data, allowing for application of a bespoke routine to maximise the acoustic data available.
The technical quality of the updated habitat map was assessed using the MESH ÔÇÿConfidence AssessmentÔÇÖ Tool2 , originally developed by a European consortium of marine scientists working on the MESH (Mapping European Seabed Habitats) project. This tool considers the provenance of the data used to make a biotope/habitat map, including the techniques and technology used to characterise the physical and biological environment and the expertise of the people who had made the map. In its original implementation it was used to make an auditable judgement of the confidence that could be placed in a range of existing, local biotope maps that had been developed using different techniques and data inputs, but were to be used in compiling a full coverage map for north-west Europe. Where two of the original maps overlapped, that with the highest MESH confidence score would take precedence in the compiled map. |