Penguins, albatrosses, petrels, elephant seals and fur seals are marine top predators that have to come on land to reproduce. Therefore, they are the only marine top predators that can be studied from land base sites, making them the most accessible convenient models to study marine ecosystems. Indeed, seabirds and seals are considered as good indicators of changes in ecosystems at differential spatial and temporal scales. However, current conservation measures, which comprise relatively few impact mitigation actions and restricted protection of the sole coastal areas, are insufficient, especially for the oceanic realm. Today, there is an urgent need to identify and protect the open sea environments where seabirds and marine mammals forage.
The first stage of most conservation planning is to identify areas that warrant protection (including areas that are already protected). The main criteria used to identify such areas are biological diversity (species richness), rarity, population abundance, environmental representativeness and site area. Where distribution data are both comprehensive and accurate, it is possible to identify areas of high species richness (hotspots), focusing on threat level (endangered species).
This Atlas of top predators from the French Southern Territories in the Southern Indian Ocean is a summary of information on the use of the southern Indian Ocean by 22 seabirds and seals species: king penguin, gentoo penguin, Adelie penguin, eastern rockhopper penguin, northern rockhopper penguin, macaroni penguin, Amsterdam albatross, wandering albatross, black-browed albatross, Indian yellow-nosed albatross, light-mantled albatross, sooty albatross, southern giant petrel, northern giant petrel, southern fulmar, Cape petrel, snow petrel, white-chinned petrel, grey petrel, brown skua, southern elephant seal and Antarctic fur seal.
The distribution map of each species was obtained by the use of tracking methods that allow identifying important areas in the southern Indian Ocean. The determination of zones of high species richness suggests several important areas for top predators. First the breeding colonies and surrounding zones: Amsterdam and Saint Paul Islands, Marion and Prince Edward islands and the Del Cano Rise, Crozet Islands, Kerguelen Plateau and East Antarctica (Adelie Land sector). Second, the upwelling-current zones: Benguela and Agulhas Currents Systems and third several the oceanic zones: the Southwest Indian Ridge (East Bouvetoya and the North Subtropical Front), the Mid-Indian Ridge (North of Kerguelen and the Eastern Indian Ocean, the Southeast Indian Ridge (Great Australian Bight and Tasmania, Ob and Lena Banks, and East Antarctica (Prydz Bay - Queen Maud Land sectors, Adelie Land sector).
The analysis of distribution indicates that some pelagic species have a much wider foraging range outside the breeding season than during the breeding season (some disperse over very large areas, i.e. wandering albatross). This highlights the urgent need to strengthen collaborations, namely between conservation and management organisms such as CCAMLR and the fisheries organisations (RFMOs), to ensure the protection of these species and the conservation of the ecosystem that will also be beneficial for many other species.
In conclusion, although this inventory of areas of key importance is preliminary because of the lack of data on several keystone species such as burrowing petrels which could not be studied in this work, the results presented here show an unprecedented improvement in the identification of priority areas within the Southern Indian Ocean, which should be the primary targets of site-based conservation efforts in the near future. The Southern Indian Ocean is not pristine. The most serious threats are linked to industrial fishing activities, including fishery discards, bycatch of seabirds and marine mammals, as well as, in a lesser extent, degradation of marine environments through global and local pollution. On land, alien introductions and diseases are now the main threats. Despite much improvement in the conservation measures taken by several fisheries, especially in the southern part of the Indian Ocean, fisheries continue to exert an important negative influence on several seabirds, especially on the high seas. However climate change is now increasingly considere to have a negative impact on seabirds at some Antarctic and sub-Antarctic localities.