African Penguin_Robert Pastryk

The African penguin (Spheniscus demersus) is currently endangered. Photo by Robert Pastryk.

Endangered Species Day is celebrated annually every third Friday of May and thousands of people around the world participate by taking action to protect threatened and endangered species. While are very used to hearing these concepts, we rarely know, what they actually mean. So, what do they mean, who defines the criteria for a species to be “threatened” or “endangered” and who monitors it?


The Red List of the International Union for Conservation of Nature (IUCN)

The assessment of species’ extinction risk is based on the methodology of the Red List of the International Union for Conservation of Nature (IUCN). The IUCN is the world’s oldest and largest environmental protection organization, founded in 1948, and is currently present in more than 160 countries around the world.

The IUCN Red List of Threatened Species is a comprehensive and objective tool for measuring the state of biodiversity on the planet. It defines the conservation status of species according to their relative risk of extinction (i.e. indicating whether the species still exists and how likely is to become extinct in the near future) in order to define necessary conservation actions, projects and political decisions.

To determine whether priority conservation activities are needed to improve the determined status, the following factors are also taken into account: the economic viability and probability of success of conservation actions, the existence of international agreements, the effects that the disappearance of the species would have on the world’s population and its ecological, phylogenetic, historical and cultural importance.

Which species are being evaluated?

It is estimated that there are 8-15 million species on the planet, but we only know about 2 million! It is therefore not possible to study and categorize the totality of taxa and species existing in the world. In fact, even many of the known species have not yet been evaluated due to a lack of information. For this reason, the Red List is based on the status of higher vertebrates (mammals, birds and amphibians) following the concept of the “barometer of life“. This idea concludes that by assessing and monitoring the conservation status of some 160,000 species, we can determine the overall state of biodiversity on the planet over time.

To date, more than 134,400 species have been assessed for the IUCN Red List. While this is an incredible achievement, there are still 25,000 more to go to reach this target.

This brings us to the question of what can (and what can’t) actually be evaluated and included on the Red List:

  • All described taxa (species, subspecies, varieties) can be evaluated.
  • Undescribed species can be evaluated only if there is an ongoing scientific description, there is information on their geographic range and their evaluation would be beneficial to their conservation status.
  • Introduced species: only wild populations introduced with conservation purposes are included in the Red List. Fig. 1 & 2 show two examples of successful translocations (movements and releases of species with a clear conservation objective). Species introduced outside their natural range for purposes other than environmental conservation cannot be evaluated.
  • Microorganisms cannot be evaluated.
  • Captive populations are not evaluated.

Species assessments can be conducted with a global or regional approach. The main idea of the Red List is to assess the largest possible area and number of species throughout the world, but sometimes the study of smaller populations is vital as well. For example, monitoring the conservation status of endemic species (natives to a single defined geographic location) is fundamental to ensure the good health of the planet’s biodiversity.

Left: Fig. 1: Montipora digitata, a Scleractinian coral abundant in shallow reef areas of the Philippines is used for translocations due to its resistance to waves and suitability for the reconstruction and conservation of coral reefs. Photo by Franklin Dattein. Right: Fig. 2: Cottus perifretum, a fish with a very precarious conservation status and thought to be extinct, was successfully reintroduced in the Demer river basin (Belgium) to prevent the loss of its unique population. Photo by Piet Spaans.

Species classification

The first step is to collect and analyse as much information as possible about the particular species, such as biology, ecology, taxonomy, etc. The next step is the analysis of the collected information, which involves the assessment of the conservation status of species. This process is carried out by scientists, evaluators and reviewers. Sometimes, other collaborators, authorities and research project managers around the world are also involved.

In that process, the data is measured against the IUCN’s criteria for the inclusion on the endangered species list which – inter alia – mainly consists of the following five key indicators: its population trends (the overall increase or decrease in the population over time), population size (number of individuals remaining), population structure (number of individuals by age), geographic distribution area, availability of necessary habitats or their actual and potential threats. The study of how these factors change or have changed over time, taking into account the biological characteristics of the species and the threats to which they are subjected, is what determines their classification.

After the evaluation, the species are classified into 9 categories, depending on their relative risk of extinction (Fig. 3). The species classification categories are:

  • Extinct (EX): No reasonable doubt that the last individual has died.
  • Extinct in the Wild (EW): Known only to survive in captivity, cultivation or well outside its natural range.
  • Critically Endangered (CR): Facing extremely high risk of extinction in the wild.
  • Endangered (EN): Facing a very high risk of extinction in the wild.
  • Vulnerable (VU): Facing a high risk of extinction in the wild.
  • Near threatened (NT): Close to qualifying for a threatened category in the near future.
  • Least Concern (LC): Population is stable enough that it is unlikely to face extinction in the near future.
  • Data Deficient (DD): Not enough information on abundance or distribution to estimate its risk of extinction.
  • Not evaluated (NE): Most of the species are still not evaluated.
African Penguin_Robert Pastryk

Fig. 3: Categories in which species are classified according to their conservation status. Source: IUCN.

Of all species evaluated in the Red List, 37,400 are threatened with extinction (about 28%). When we look at different groups across the living world, 41% of amphibians, 36% of sharks and rays, 34% of conifers (e.g., pine trees), 33% of coral reefs, 28% of crustaceans, 26% of mammals and 14% of birds are currently considered to be threatened with extinction. Moreover, it is estimated that about 1 million species are on the brink of extinction. This estimation takes into account the large number of species that are not yet known or could not be assessed.

Over time, species may move within the categories on the Red List. To check their conservation status, re-evaluations are recommended at least every 10 years. These studies can be done by species or by groups of species, for which the Red List Index (RLI) was developed. The most vital to re-evaluate periodically are the threatened categories (CR, EN, VU) to assess if their status has improved or declined.

The Red List acts as a detector of urgent cases. It identifies species on the brink of extinction to prioritize conservation actions and prevent their total disappearance. The ultimate goal is to get as many species out of the threatened categories as possible to ensure the health of the planet’s biodiversity.

Successful examples of endangered species conservation

But there is good news! Some species that were previously on the brink of extinction have significantly improved their conservation status as a result of the successful implementation of restoration projects. Improving their habitats, eliminating threats and invasive species or reintroducing specimens have allowed for an increase of their population size and reducing their risk of extinction. The following are some encouraging examples that conservation actually works, if done correctly!

  • Barndoor skate (Dipturus laevis): A marine ray native to the eastern coasts of the United States and Canada. Due to the incidental catch by groundfish fisheries, its conservation status was defined as Vulnerable (VU) in 2000 and Endangered (EN) in 2003. However, the number of individuals has increased due to the monitoring and reduction of this type of fishing. Currently, it is classified as Least Concern (LC).
  • Giant panda (Ailuropoda melanoleuca): This mammal native to the Asian continent has recently been classified as Vulnerable (VU). This may sound like bad news, but its conservation status has actually improved considerably, as it was categorized as endangered (EN) for almost 20 years. Today, there are about 500-1000 mature individuals (with reproductive capacity) and its population size is increasing. This has been made possible through the efficient protection and reforestation programs conducted in China. However, it is essential to sustain these conservation measures, as climate change is expected to have a strong influence on the destruction of their natural habitat.
  • Juan Fernández Fur Seal (Arctocephalus philippii): This mammal inhabits the coasts of western South America (Perú, Chile). Until the end of the 19th century, they were hunted to the brink of extinction for their pelts. Very few individuals were seen in the early 20th century and the species was thought to have become extinct shortly thereafter. Years later, new individuals were observed and the Juan Fernández Fur Seal hunt was banned in 1965, allowing for its incredible recovery. Today, it is no longer considered an endangered species, being classified as Least Concern (LC). There is an estimated total of 16,000 mature individuals, with a growing population trend.
  • Humpback whale (Megaptera novaeangliae): Who doesn’t know this magnificent whale that lives in almost all of the world’s oceans!? Its large-scale exploitation led to a rapid decline in its population size, putting it in the threatened categories for many decades. Its hunting was banned in 1968, with the adoption of important international protection measures. Despite having been severely reduced to a world population in the low thousands at that time, humpbacks have recovered strongly to an estimated 84,000 mature animals which is increasing. Humpback whales enjoy additional protective measures, such as sanctuaries, in several countries. The species is also listed in global conservation agreements. Its latest assessment (2018) classified it as Least Concern (LC).

Today, these species are out of danger of extinction thanks to the implemented conservation measures. However, this may change in the future. That is why re-evaluations are so important to detect changes in threats, the effects of conservation measures or the impacts of natural events, among other factors.

Fig. 4: Barndoor skate. Photo by Phillip BlackmonFig. 5: Giant panda. Photo by Joachim S. MüllerFig. 6: Juan Fernández Fur Seal. Photo by Jim Thorsell; Fig. 7: Humpback whale. Photo by Rui Freitas.

The state of the oceans

The world’s oceans have faced important threats over several decades. Some of the most impactful are overfishing, habitat degradation, sewage and plastic discharge, industrial development and carbon dioxide pollution. These phenomena have degraded marine life, impacting the health of ecosystems and their biodiversity.

By 2021, 14,395 marine species have been assessed according to the IUCN Red List (Fig. 8). 9,852 species (68.4%) have been classified as Least Concern (LC), 463 (3.2%) Near Threatened (NT) and 1,136 (7.9%) are in the threatened categories. Out of these, 149 are classified as Critically Endangered (CR), 287 as Endangered (EN) and 700 as Vulnerable (VU). However, it is important to remember that these are only the species for which there was sufficient information and that most species have not yet been evaluated due to a lack of data and further studies.

In 2016, more than 130 local and global marine extinctions were documented. Furthermore, the impact of climate change is expected to severely affect 60% of marine biodiversity by 2050. It is therefore urgent and necessary to take conservation measures to protect marine life, to ensure the good health of the oceans and the rest of the planet.

To that end, the scientific community recommends the following measures:

  • The establishment of more efficient Marine Protected Areas.
  • The elimination of illegal and unregulated fisheries and markets for aquatic species.
  • A significant reduction in carbon dioxide emissions.

Fig. 8Conservation status of marine species assessed according to the IUCN Red List (2021).

What can You do to help?

To help threatened and endangered species to recover is a collective effort and responsibility. Therefore, You can make a difference! Here are some ways you can help:

  • Learn about the threatened species in your area (and globally) and the threats they face.
  • Observe wildlife in a non-harmful, non-invasive and responsible way. Make informed consumer decisions about wildlife viewing and view marine life from a safe distance.
  • Find a habitat and species conservation project in your area and volunteer for restoration projects. A safe and healthy habitat is the most important thing for the protection and conservation of species.
  • Never buy anything made from a threatened or endangered species.
  • Report observations of invasive species in your area to local authorities, such as municipalities, NGOs or universities.
  • Reduce the amount of pollution you generate and participate in coastal clean-up events.
  • Plant trees native to your area.
  • Use water and electricity responsibly.
  • Refuse, reduce, reuse and recycle (the 4R principle).
  • Don’t use products tested on animals.
  • Stay informed and spread the word! Endangered Species Day is a great opportunity to get the message out and take action.

What are your thoughts? Let us know in the comment section!


  • International Union for Conservation of Nature (IUCN) (
  • IUCN, S. S. C. (2001). IUCN Red List categories and criteria: version 3.1. Prepared by the IUCN Species Survival Commission. Available at:
  • IUCN Standards and Petitions Committee. 2019. Guidelines for Using the IUCN Red List Categories and Criteria. Version 14. Prepared by the Standards and Petitions Committee. Downloadable from:
  • Endangered Species Coalition (
  • Swan, K. D., McPherson, J. M., Seddon, P. J., & Moehrenschlager, A. (2016). Managing marine biodiversity: the rising diversity and prevalence of marine conservation translocations. Conservation Letters, 9(4), 239-251.
  • Vught, I., De Charleroy, D., Van Liefferinge, C., Coenen, E., & Coeck, J. (2011). Conservation of bullhead Cottus perifretum in the Demer River (Belgium) basin using re‐introduction. Journal of Applied Ichthyology, 27, 60-65.
  • Cheung, W. W., Lam, V. W., Sarmiento, J. L., Kearney, K., Watson, R., & Pauly, D. (2009). Projecting global marine biodiversity impacts under climate change scenarios. Fish and fisheries, 10(3), 235-251.