Online sub-Antarctic workshop on pelagic regionalisation – 1 June 2022

Workshops were held in 2020 and 2021 between French and South African partners to refine the pelagic work packages planned for WP1: Ecoregionalisation within the subantarctic pelagic realm. Funding from ASOC (Antarctic and Southern Ocean Coalition) was granted to finance a short-term project “Ecoregionalisation of the Eastern Sub Antarctic Region” from Nov 2021-Aug 2022 with specific objectives to (1) Develop a spatial understanding of the mesopelagic ecosystem in the epi- and mesopelagic zones across the CCAMLR subantarctic Indian Ocean region, and (2) Determine how the distribution of plankton and mesopelagic fish communities support the foraging strategies of a suite of marine predators including seabirds and marine mammals. The current workshop focused on determining ecoregions in the subantarctic oceanic zones based on the mapping of abiotic and biotic layers to evaluate boundaries of ecoregions: abiotic layers included geography, geomorphology, and oceanography, while biotic features include primary production, plankton, acoustics, and top predators. Focused work packages for this ASOC-funded project are (1.1) Analyse oceanographic regions based on the abiotic characteristics of the Indian subantarctic zone, with the planned output being an Atlas of geographic layers from oceanographic data compiled from satellite data and international water climatological databases; (1.2) Identify pelagic ecoregions including for plankton and pelagic fish of the Indian subantarctic zone through data analysis of net and CPR samples, with the planned output being an Atlas of pelagic ecoregions compiled from net samples and occurrences registered in international databases; and (1.3) Analysis of acoustic measurements from echosounders, with the output being Maps of acoustic densities and regions. Analysis of RAATD (Retrospective Analysis of Antarctic Tracking Data) data and the at-sea distributional maps of both seabirds and mammals (1.4) will be investigated with other scientists involved in specific projects concerning IMMAs (Important Marine Mammals Areas), KBA (Key Biodiversity Areas), AES (Areas of Ecological Significance), an ecoregionalisation using seabird and mammal habitat importance, abundance
and distribution using information obtained through at-sea observations. The funding from ASOC has
enabled the initiation of plankton and acoustic analyses for the western part of the area of investigation, which is data-poor relative to the eastern component. Another project will be needed for work package 1.5. to synthesise all the existing information. Discussions also considered the impact of climate change on the biota of the subantarctic islands. This workshop however had a discussion to consider another layer on climate change that are recognized as being important in the subantarctic area, with major potential future changes to the ecosystem. Two presentations were given on the potential layers of the climate change scenarios: primary production and warming and marine heatwaves. This report will summarise the outcome of the 2022 workshop.