In Situ Benthic Image Transects from the Disko Fan Conservation Area in the Davis Strait (Eastern Arctic)
Description
In 2012 and 2013, Fisheries and Oceans Canada conducted benthic imagery surveys in the Davis Strait and Baffin Basin in two areas then closed to bottom fishing, the Hatton Basin Voluntary Closure (now the Hatton Basin Conservation Area) and the Narwhal Closure (now partially in the Disko Fan Conservation Area). The photo transects were established as long-term biodiversity monitoring sites to monitor the impact of human activity, including climate change, on the region’s benthic marine biota in accordance with the protocols of the Circumpolar Biodiversity Monitoring Program (CBMP) established by the Council of Arctic Flora and Fauna. These images were presented in a technical report that summarises the epibenthic megafauna found in seven image transects from the Disko Fan Conservation Area: Baker, E., Beazley, L., McMillan, A., Rowsell, J. and Kenchington, E. 2018. Epibenthic Megafauna of the Disko Fan Conservation Area in the Davis Strait (Eastern Arctic) Identified from In Situ Benthic Image Transects. Can. Tech. Rep. Fish. Aquat. Sci. 3272: vi + 388 p. Taxa from ten phyla (Annelida, Arthropoda, Brachiopoda, Bryozoa, Chordata, Cnidaria, Echinodermata, Mollusca, Nemertea, Porifera) were identified from the imagery and reported on a per photo basis in v.4. That data was analyzed to comply with CBMP recommendations. The average abundance (N), number of taxa (S), Margalef d, Shannon Diversity and Simpson’s Index with their Hill equivalents, and Pielou’s Evenness, were calculated for each transect. Bray-Curtis similarity in community composition among transects was calculated from log(x+1)-transformed standardized abundance. UPGMA cluster analysis identified three significantly different depth-related clades. S, N and d were significantly negatively correlated with depth. That work is summarized in: Kenchington, E., Lirette, C., Treble, M., and Jacobs, K. 2022. Biodiversity Monitoring Stations for Benthic Megafauna in the Disko Fan Conservation Area. Can. Tech. Rep. Fish. Aquat. Sci. 3499: v + 75 p. In this v.4 update the abundance of taxa in each photo are provided. Those data can be used to calculate the indices summarized in the 2022 report.
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Details of how these image were collected and analyzed can be found in the technical report: Baker, E., Beazley, L., McMillan, A., Rowsell, J. and Kenchington, E. 2018. Epibenthic Megafauna of the Disko Fan Conservation Area in the Davis Strait (Eastern Arctic) Identified from In Situ Benthic Image Transects. Can. Tech. Rep. Fish. Aquat. Sci. 3272: vi + 388 p. The images examined in this report came from seven image transects conducted within the former Narwhal Over-wintering Deep-Sea Conservation Area in Baffin Bay. The depths at which images were collected ranged from 400-1000 metres, with individual transect lines running along depth contours of 400 metres, 600 metres, or 1000 metres. Transects were 1-2 kilometres in length. The image data were obtained using the 4K-Camera, or 4KCam , an underwater drop camera system consisting of a high-resolution digital camera (Canon Rebel Eos Ti 12 megapixel) and two flashes enclosed in a cage that permits it to collect images at depths of up to 4 kilometres below the sea surface (Beazley and Kenchington, 2015). The 4KCam was deployed on a winch line over the side of the vessel and towed above the seafloor. The 4KCam’s distance from the seafloor was controlled by raising and lowering the winch line, and the camera and flashes were triggered to collect images each time the lead weight attached to the system made contact with the bottom. Images were collected at 30-60 second intervals for each transect line. As there was no feed to the vessel, all photo locations were blind drops. Each image was assigned a photo file name that consisted of the Consecutive Operation Number (CON) that was associated with the transect and an image number. The images from each transect were examined for their quality prior to analysis, and those that were too dark, too high off the bottom were discarded. Images obscured by sediment clouds covering at least half of the photo were also not analysed. The remaining images were corrected in Adobe Photoshop CS2 using the AutoLevel and SharpenMore functions to optimise their contrast and exposure levels, colour balance, and sharpness. A 4x3 grid layer dividing each image into twelve square cells labeled A-L was then superimposed on each image using batch-processing and Adobe Action Sets, followed by a layer of twelve 1-cm scale bars. Due to the inverse halo effect, a consistent band of cells at the bottom of each image (I-L) was darker than the cells above it (A-H). When analysing the bottom cells, the brightness was increased by 20-25% and the contrast was altered by +10%. The images in this dataset all have these conditions applied to them and include the grid and scale bar overlays. The data extracted from the images is now available in v.4. Those data can be used to calculate the diversity indices summarized in the technical report: Kenchington, E. et al. 2022. Can. Tech. Rep. Fish. Aquat. Sci. 3499: v + 75 p.