Current knowledge of New Caledonian marine and freshwater ichthyofauna, SW Pacific Ocean: diversity, exploitation, threats and management actions

Located in the Southwest Pacific Ocean, the New Caledonian archipelago hosts a diversified and original ichthyofauna. Marine ecosystems host 2,339 species of fish, including ~1,450 for coral reefs alone and a total of 94 endemics, especially in deep environments. The proximity of the centre of biodiversity (the “coral triangle”), as well as a great variety of coastal habitats and their relatively good “state of health” are probably major reasons for this high species richness. Freshwaters (excluding estuaries and brackish water) have 94 species, including 12 introduced and 8 endemics. Most of these species are diadromous, essentially amphidromous, and illustrate biological traits adapted to local rivers. New Caledonian ichthyofauna is subject to various disturbances of varying intensity and/or frequency. Some disturbances are natural and affect habitats rather than the fish species, such as cyclones, which can affect both coastal ecosystems (coral reefs, seagrass beds, mangroves) and freshwater ecosystems. Anthropogenic pressures on ichthyofauna are of several natures. Fishing is widely practiced, both in rivers and in coastal environments and in the EEZ, but does not currently seem to pose a serious threat to targeted populations. New Caledonian aquaculture is largely focused on shrimp farming, but fish farming (currently marginal) could develop in the near future. Mining activities related to the extraction of nickel ore (and cobalt to a lesser extent) are however a much more serious problem. The potential impacts of these mining activities differ from those of cyclones, in particular by their regular (if not permanent) and non-punctual nature on the one hand, and by the fact that they considerably increase the risk of contamination of freshwater and coastal environments by metallic trace elements on the other hand. These metallic elements as well as various organic contaminants (pesticides and PCBs) are indeed found in coral reef fish. Other more specific threats concern freshwater fish, such as hydraulic developments or the proliferation of certain introduced and invasive species. For all New Caledonian aquatic ecosystems, the major issue of climate change cannot be ignored, but its impacts still remain poorly documented. About 15,000 km² of coral reef and lagoon areas have been listed as UNESCO World Heritage since 2008 and are therefore protected and regulated, with regard to the activities authorized within these areas. In addition, there are more i