92be72da9620dd570cd3277b741f0573 English dataset Cornwall Inshore Fisheries and Conservation Authority Data Officer Cornwall IFCA Research Team enquiries@cornwall-ifca.gov.uk pointOfContact 2024-07-23 MEDIN Discovery metadata standard 2.3.8 urn:ogc:def:crs:EPSG::4326 2022 Cornwall Inshore Fisheries and Conservation Authority (IFCA) on behalf of Cornwall Wildlife Trust Gerrans Bay Acoustic Survey of the seagrass bed 2022-10-04 publication 2022_CIFCA_MX_GER_Seagrass Cornwall Inshore Fisheries and Conservation Authority (Cornwall IFCA) was contracted by Cornwall Wildlife Trust to map the extent of the seagrass within Gerrans Bay as part of their blue carbon mapping project. The survey site is within the Falmouth Bay to St Austell Bay Special Protection Area (SPA). This project was funded as part of the G7 Legacy Fund. The contract includes joint intellectual property (IP) of all data collected. The aim of the survey was to map the extent and coverage of the seagrass bed within Gerrans Bay using a Biosonics MX Scientific Echosounder. In total 170 acoustic survey lines were completed, all of which were included in the analysis. Research Team Cornwall IFCA Cornwall Inshore Fisheries and Conservation Authority enquiries@cornwall-ifca.gov.uk originator Research Team Cornwall IFCA Cornwall Inshore Fisheries and Conservation Authority enquiries@cornwall-ifca.gov.uk custodian irregular Marine Environmental Data and Information Network NDGO0005 Habitats and biotopes GEMET - INSPIRE themes, version 1.0 2008-01-06 revision Habitat extent SeaDataNet P021 parameter discovery vocabulary 2009-11-16 revision Data is freely available for research or commercial use providing that the originators are acknowledged (Cornwall IFCA and Cornwall Wildlife Trust) in any publications produced and permission must be sought if the data will be reproduced in full or part or if used in any analyses. otherRestrictions No restrictions to public access English biota Charting Progress 2 Sea Areas 2009-06-18 creation Western Channel and Celtic Sea ICES Rectangles 2009-05-01 creation 29E5 SeaDataNet vertical extent keywords 2010-01-01 revision water column -4.9663 -4.9262 50.1865 50.2050 2022-07-20 2024-07-28 4.2000 17.3000 Research Team Cornwall IFCA Cornwall Inshore Fisheries and Conservation Authority enquiries@cornwall-ifca.gov.uk distributor dataset MEDIN data guideline for sidescan sonar (SSS) data 2012-04-30 publication See the referenced specification true Previous survey positions (polygons and points) were uploaded onto HYPACK MAX Version 2019 software. For each polygon, survey lines were created depending on the aspect of each individual bed so that the survey lines ran perpendicular where possible to the coastline following the Environment Agency methodology of subtidal seagrass monitoring for the Water Framework Directive (WFD) (Environment Agency, 2019). Each survey line ran further than the known extent of each bed to capture any changes to the bed extent since they were last surveyed. The survey lines were set up with 20 meter line spacing. Acoustic data was acquired using a MX Aquatic Habitat Echosounder (Appendix 2). The acoustic data was captured using Biosonics’ Visual Aquatic (V 6.4) software. Visual Aquatic analyses the E1 and E2 values to provide estimates of submerged aquatic vegetation (including seagrass), substrate and bathymetry data. The transducer was deployed over the port side of the vessel via a pole mounted on the side, the pole positioned the transducer approximately one metre below the keel to ensure no part of the vessel caused any acoustic shadowing. Acoustic data was collected in one survey area to map the extent of the bed. On arrival within Gerrans Bay, a Valeport Swift Sound Velocity Profiler was deployed to measure the Conductivity, Temperature, and Depth (CTD). Once recovered to deck the data was downloaded using Valeport Data log X2 software and the temperature and salinity values from the bottom depth were input into the Visual Acquisition software. A folder for the survey area was created prior to the deployment of the MX and data was recorded with date and time stamps for each file e.g. 20220728_080534. A target was created in HYPACK to indicate the start of line (SOL); this was repeated at the end of line (EOL). The speed over ground was aimed to be at a constant of 4.5 knots so that the pings from the MX were at a consistent distance. MX SOL and EOL positions, targets for verification and video tow SOL and EOL positions were recorded in the Lat/Long WGS84 projection taken from a single GPS, Hemisphere V500 GNSS system on Tiger Lily VI. HYPACK targets were extracted as a .txt file format and opened in Microsoft Excel (comma delimited). The video files and raw MX files (.dt4 and .rtpx) were transferred from the PC to a WD Passport for transport and storage at the end of each survey day. The log sheets were worked on from the shared network drive and saved at the end of each day. A total of 170 lines were completed, all of which were included in the analysis. All lines for each bed were loaded into Biosonics’ Visual Aquatic software in a batch, then analysed individually. Quality assurance (QA) was carried out for tows individually and the bottom line and plant line were manually adjusted where there were errors. The plant line was adjusted when anything other than seagrass was present such as algae, noise in the water column when the vessel was turning and fish in the water column. Once each line was corrected, the post processing information was recorded in the survey log. The analysed data were exported from Visual Aquatic as a .csv file. Each data point in the .csv file represented the average values of ten consecutive acoustic pings. The data was copied to Microsoft Excel pasted to columns with corrected headers including latitude, longitude, date, time and notes. This was saved as a .xls file and imported into MapInfo Professional Advanced (Version 17.0.4) to create points. A theme was added to the points data for the plant height (m) and the plant coverage (%). A polygon was drawn around each survey area clipped to the point at the start and end of each tow. A raster was created using the natural neighbour function for plant height (m) and plant coverage (%). The settings for the raster were distance: 20 m, smoothing: 0, clipped to polygon for each survey area, cell size: user suggested and interpolated along edges. Advanced colour was used to define the colour scales. Plots were created for points of plant height (m), percentage cover (%) of seagrass, contour plot of plant height (m) and the contour plot of percentage cover of seagrass (%).