The “Expert Workshop on Pelagic Spatial Planning for the eastern subantarctic region (Domains 4, 5 and 6)” was held in Cape Town ( South Africa) between 26th and 30th August 2019. The workshop developed a scientific work program that will result in both pelagic abiotic and biotic classifications of the Planning Domains using geographic, biological and oceanographic features. Distributions of plankton, mesopelagic fish and top predators were considered to be relevant to future ecoregionalization showing latitudinal patterns of communities for the pelagic species. The importance of frontal zones such as the Antarctic Polar Front, Subantarctic Front and the Subtropical Front were highlighted. The latitudinal zonation of bioregions (based on abiotic and chlorophyll clustering) according to frontal zones may be influenced by climate change and will influence the spatial distribution of pelagic assemblages. This will have consequences for marine bird and mammal populations as it will change the habitat of their main pelagic prey species (e.g. euphausiids, squids, mesopelagic fish, etc.).
The workshop highlighted that ecoregionalisation which combines abiotic regionalisation (or bioregionalisation) and species biogeographical distributions has to be conducted at the scale of plateaus and oceanic zones between them which includes areas outside the national jurisdiction i.e. a more detailed level than what has been done to date. High productive pelagic areas must be considered in relation to the bathymetry, iron enrichment, fronts and island mass effects, which contrast with high nutrient low chlorophyll areas farther south.
The subantarctic islands are known to support substantial colonies of seabirds and seals, which for several species have global importance. The high productivity in the vicinity of the islands, together with the large aggregations of seabirds and seals found at the islands, attract various other animals, e.g. several cetaceans, to their vicinity. The populations of several seabirds that breed at the islands have decreased. Although there is cumulative evidence that decreases of albatrosses and petrels have been substantially influenced by by-catch mortality in fisheries, the decreases in some penguins are probably attributable to decreased availability of prey. Thus, the workshop reported herein represents the logical progression of previous work conducted (WG-EMM 12/33) towards addressing these considerations. Specifically, the workshop developed a detailed and logical plan of scientific work that will lead to a regional (i.e. pan-subantarctic) overview of ecosystem structure and function which can be used in any future spatial conservation planning or risk assessments in such a dynamic pelagic environment.