IUCN Risk Assessment

Approximately 230,000 (15%) of the 1.8 million known species worldwide are marine species, and there may be up to ten times as many that remain to be discovered. Marine species face increasing risks of extinction caused by changing climate, ocean acidification, overexploitation, habitat destruction, pollution, and alien species.

The International Union for the Conservation of Nature and Natural Resources (IUCN) began assessing Risk of Extinction levels in 1973. Species assessments are carried out by Specialist Groups, comprised of scientists, who participate in workshops where conservation actions for each species are evaluated according to data on population trends, distribution, life history, past and existing threats, taxonomy, and ecology. These factors determine if a species meets the criteria to be listed within a threatened category under the IUCN Red List of Threatened Species.

•      The IUCN Red List Categories include eight levels of extinction risk:

•      Extinct (EX)

•      Extinct in the Wild (EW)

•      Critically Endangered (CR)

•      Endangered (EN)

•      Vulnerable (VU)

•      Near Threatened (NT)

•      Least Concern (LC)

•      Data Deficient (DD)

The IUCN determines whether or not a species qualifies for a particular threat category by deciding if it meets the threshold for that category in one of five criteria (A-E). Critically Endangered species face an extremely high risk of extinction in the wild. The other threatened categories – Endangered and Vulnerable – refer to species that are either at a very high, or high, risk of extinction in the wild.

Specifics regarding criteria for all threatened categories can be found on the IUCN Red List website.

As of 2007, only about 1,500 of the 41,500 plants and animals assessed under the IUCN Red List Criteria were marine species. To address this gap, IUCN, Conservation International and Old Dominion University initiated the Global Marine Species Assessment (GMSA) in 2006, with the goal of completing IUCN Red List assessments for 20,000 marine species by 2012.

Working with IUCN Specialist Groups, GMSA has completed assessments of all the world’s known species of sharks and rays, groupers, and reef-building corals (Polidoro et al. 2008). However, several species in these groups are of unknown status due to lack of information and many taxonomic groups still await assessment.

Which Goals Does This Affect?

How Was It Measured?

The Ocean Health Index utilized data for the 2,377 marine species categorized in the IUCN Red List. The main taxonomic groups included were: habitat forming corals, mangroves, seagrasses, sea snakes, marine mammals, seabirds, marine turtles, angelfish, butterflyfish, groupers, wrasses, parrotfish, hagfish, and tuna and billfishes.

The average extinction risk was calculated as the weighted sum of the International Union for Conservation of Nature’s (IUCN) assessments of species.  Weights used were based upon the level of extinction risk following Butchart et al. 2007: EX (extinct) = 0.0, CR (critically endangered) = 0.2, EN (endangered) = 0.5, VU (vulnerable) = 0.7, NT (not threatened) = 0.9, and LC (least concern) = 0.99.

For the status of the Species sub-goal of the Biodiversity goal, the average risk status of species assessed was used. The status of the Iconic Species sub-goal of Sense of Place was calculated as the average extinction risk of those species identified as iconic.

The average risk status was also used as a proxy for ecological resilience in the Carbon Storage goal, Coastal Protection goal, Fisheries sub-goal of Food Provision, Iconic Species sub-goal of Sense of Place, Natural Products goal, Habitat Diversity sub-goal of Biodiversity and Artisanal Opportunities goal. In the case of Natural Products and Artisanal Opportunities, as these are mostly linked to coastal systems that are easily accessible from the shore, the calculation was limited to the species in the marine area within 3nmi of the coastline.

More species will be assessed in the future, but it will require a significant amount of time to complete assessments for every relevant group, and additional time will be necessary to assemble information on newly discovered species.

Get More Information

The Convention on Biological Diversity (CBD)
CBD provides a strategic plan for the conservation of biological diversity and the sustainable use of its component factors on local, national, and international scales. 


PHOTO(S): © Keith A. Ellenbogen
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