Brief description
The principle aim of this project was to map the fine-scale spatial distribution of key abalone habitat impacted by urchins in < 25 m water depth using multibeam acoustic imagery. Detailed substrate type (Pavement Reef, Megaclast Reef, Mixed Consolidated Sediment/Reef and Sand), and kelp coverage maps have been produced for the east coast of Tasmania. Large urchin barrens have been predicted and the minimum quantifiable unit of which small incipient barrens can be detected has been identified using this acoustic water column technique.This data provides a snapshot of the 2021 distribution of seafloor habitats and associated vegetation distribution, and will assist in the facilitation of strategic decision making for urchin control and abalone management.
Data for download has been split by fishing block (22-24, 27-30). This record describes *FISHING BLOCK 22*. The following data products are available for download, for each fishing block:
• 50cm resolution bathymetry
• 50cm resolution substrate type (Seamap Australia classification)
• bathymetry derivatives (seabed slope, curvature, rugosity, 1 and 2m contours)
• water column data - 1m mean signal
• water column data - 9m2 raw block statistic
• water column data - vegetation likelihood classification
See associated records for access to data from other fishing blocks (23, 24, 27, 28, 29, 30).
Lineage
Maintenance and Update Frequency: none-plannedA Kongsberg Maritime EM2040 multibeam sonar (contracted from CSIRO) was pole mounted on the RV Abyss (Marine Solutions) vessel. CARIS software was used to process the bathymetric data into a gridded depth surface at 50 cm resolution. The bathymetric surface was analysed in ArcGIS to produce spatial derivatives of seabed slope, curvature, rugosity and associated contour line information. These spatial derivatives are available for download as associated data with this project.
The water column data from the multibeam data record (.all and .wcd format) were read into Matlab using the open-source CoFFee toolbox (https://github.com/alexschimel/CoFFee). The water column samples were filtered using subsequent custom Matlab scripts to eliminate most of the unwanted noise while retaining targets likely to be signal from vegetation. The remaining signals were gridding by calculating the average signal within 50cm grid cells and exporting as point features at 50cm spacing. In ArcGIS, these points were re-gridded to 1m resolution using the mean signal within 1m blocks. The Block Statistic tool was run using a 3x3 neighbourhood and calculating the mean value to create a surface representing 9m2 which would be relevant to the scale that managers can relate to in the natural environment. The block statistic raster was then reclassified into three classes to represent bare (no signal in the water column), patchy (medium level signal) and dense signal (lots of vegetation). The thresholds for the three classes were -64 (minimum) to -60db as bare, -60 to -50 as patchy, and >-50 as dense.
The derived water column products are (1) 1m mean signal; (2) raw block statistic (9m2); and (3) vegetation likelihood classified ‘traffic light’ layer. Products (2) and (3) are available as layers for visualisation on the Seamap Australia data portal.
Full details of data processing methods for both the seafloor and water column acoustics can be found in the associated report with this data record.
Notes
CreditAbalone Industry Re-investment Fund (AIRF)
Tasmanian Climate Change Office
CSIRO Geophysical Mapping and Survey (GSM)
Sustainable Marine Research Collaboration Agreement (SMRCA)
Data time period: 2021-04-12 to 2021-04-23
text: westlimit=147.9; southlimit=-43.20; eastlimit=148.3; northlimit=-43.00
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(Block 22 - 50cm bathymetry [Geotiff DOWNLOAD])
uri :
https://data.imas.utas.edu.au/attachments/Abalone_habitat_warming_reefs/bathy/BLOCK22_bathy_50cm.tif
(Block 22 - finescale substratum [Geotiff DOWNLOAD])
uri :
https://data.imas.utas.edu.au/attachments/Abalone_habitat_warming_reefs/habitat/BLOCK22_habitat.tif
(Block 22 - bathymetry derivatives [zip package DOWNLOAD])
(Block 22 - water column 1m mean signal [Geotiff DOWNLOAD])
(Block 22 - water column 9m2 raw block statistic [Geotiff DOWNLOAD])
(Block 22 - water column classified [Geotiff DOWNLOAD])
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