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The Western Indian Ocean (WIO) is comprised of productive and highly diverse marine ecosystems that are rich sources of food security, livelihoods, and natural wonder. The ecological services that species provide are vital to the productivity of these ecosystems and healthy biodiversity is essential for the continued support of economies and local users. The stability of these valuable resources, however, is being eroded by growing threats to marine life from overexploitation, habitat degradation and climate change, all of which are causing serious reductions in marine ecosystem services and the ability of these ecosystems to support human communities. Quantifying the impacts of these threats and understanding the conservation status of the region’s marine biodiversity is a critical step in applying informed management and conservation measures to mitigate loss and retain the ecological value of these systems.

The International Union for Conservation of Nature (IUCN) Red List Categories and Criteria are the most widely used and objective system of quantifying the conservation status of species. For this report, Red List assessments for marine fish species were produced and compiled with existing assessments for other marine species groups to generate a comprehensive assessment of the conservation status of the marine biodiversity of the WIO. The species assessed for this report were done so through clade-based and regionally focused Red List assessment workshops involving hundreds of taxonomic experts from around the world. To supplement assessments for marine fishes of the region, three workshops were held in Tanzania, Oman and South Africa over the course of three years from 2017 to 2019. Thirty-one marine fish experts from 14 countries participated in the three workshops.

Among the more than 4,000 species assessments compiled for this report, 473 species were identified as threatened or Near Threatened with extinction at the global level, according to the IUCN Red List Categories and Criteria. Incorporating uncertainty in the true status of Data Deficient species, between 7-24% of all species were estimated as being currently at risk of extinction, with a best estimate of 8% of all assessed species being threatened. Spatial analyses of species richness across the region identified hotspots of threatened species including the southern Red Sea and the southern coast of India. Major threats were analysed amongst threatened and Near Threatened species, of which more than 90% were found to be impacted by biological resource use, largely in the form of targeted fisheries and bycatch as well as illegal, unreported and unregulated fishing activities. Overexploitation was flagged as a driver of population decline for all threatened and Near Threatened cartilaginous fishes, mammals and sea turtles. The 237 threatened and Near Threatened reef-building corals are impacted by the same suite of fishing threats, including fisheries-related habitat degradation. In general, habitat degradation and destruction through pollution, coastal development and other habitat modifications emerged as a major threat across assessed species groups. From these analyses, this report highlights trends in research needs for species in the region, including priorities for fundamental biological and ecological research and quantifying trends in the populations of species.


© 2021 IUCN, International Union for Conservation of Nature and Natural Resources.

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Original Publication Citation

Bullock, R., Ralph, G., Stump, E. ... Williams, A., Yahya, S., Carpenter, K.(2021) The conservation status of marine biodiversity of the Western Indian Ocean. Switzerland, International Union for Conservation of Nature.


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