IUCN Red List: The Practical Guide to Acting Against the Threat of Extinction

The IUCN Red List celebrates its 60th anniversary in 2025, and not all the news is good. A study published in Nature in January 2025 reveals that a quarter of the world's freshwater animals face a high risk of extinction. Fish, dragonflies, crabs, shrimp: these species, essential to our ecosystems, are silently disappearing. Faced with this urgency, the International Union for Conservation of Nature proposes a standardized methodology to assess, understand, and act. This practical guide is for anyone wishing to conduct regional or national extinction risk assessments.

Two Approaches to Assessing Extinction Risk

When establishing a regional Red List, researchers and decision-makers have two options. The first is to publish an unchanged extract from the IUCN Global Red List, including species present in the geographical area studied. This approach is particularly justified when the region has a high number of endemic species or when there is a generalized lack of reliable local data.

The second, more ambitious option, involves conducting a specific regional assessment by applying Version 3.1 criteria to locally collected data. This approach offers a more precise view of the specific threats to the territory concerned. It allows for the identification of conservation priorities adapted to the local context, a crucial dimension as climate regulations intensify.

The Five-Step Assessment Process

The IUCN methodology is based on a rigorous protocol that ensures the international comparability of assessments. The first step: collecting information on the species' geographical distribution, population size, and demographic trends. This documentary phase involves field observations, naturalist databases, and published scientific studies.

Next comes the identification of threats, whether direct or indirect. Habitat loss, overexploitation, pollution, invasive species, climate change: each risk factor must be documented and quantified. Scientists rely notably on work published in journals such as Nature or Science to contextualize these threats on a global scale.

The third step constitutes the technical core of the assessment. Experts apply the quantitative criteria A to E defined by the IUCN:

• Criterion A: observed, estimated, or projected population decline
• Criterion B: restricted geographical range and decline or fragmentation
• Criterion C: small population and continuing decline
• Criterion D: very restricted population or limited to a few sites
• Criterion E: quantitative analysis of extinction risk

These criteria allow for the assignment of a threat category among those defined by IUCN: Least Concern (LC), Near Threatened (NT), Vulnerable (VU), Endangered (EN), Critically Endangered (CR), Extinct in the Wild (EW), or Extinct (EX). An additional category, Data Deficient (DD), applies when available information does not allow for a reliable assessment.

From Assessment to Action: Recommendations and Monitoring

The assignment of a category is not an end in itself. The fourth step consists of drafting a detailed report integrating recommended conservation measures, action priorities, and research needs. This document becomes an operational tool for natural area managers, local authorities, and nature protection associations.

"The lack of data on freshwater biodiversity can no longer be used as an excuse for inaction," emphasizes Catherine Sayer, IUCN Freshwater Biodiversity Officer.

The fifth step, often overlooked, is nevertheless crucial: the regular reassessment of classified taxa. Near Threatened species or those classified as Data Deficient require particular monitoring. Scientific knowledge evolves, threats transform, and conservation strategies must adapt accordingly. The regional guidelines guide specifies the recommended intervals between two assessments.

A Living Barometer of Planetary Health

Since its creation in 1964, the Red List has become much more than a simple inventory of threatened species. It constitutes the planetary "barometer of life," a tool that measures the pulse of biodiversity and guides conservation policies worldwide. More than 160,000 species have been assessed to date, the result of an extraordinary collaboration bringing together thousands of experts, partner institutions, and committed donors.

The Red List data directly influence political and economic decisions. They make it possible to identify priority areas for conservation, guide international funding, and evaluate the effectiveness of protection measures. Companies also use them to assess their impacts on biodiversity, a dimension increasingly integrated into decarbonization strategies.

Methodological Challenges of Regional Assessment

Applying global criteria at the regional level raises specific methodological questions. A species may be locally abundant while being globally threatened, or vice versa. The IUCN guide recommends adjusting regional categories by taking into account migratory flows and populations present in adjacent territories.

Regional assessments must also consider the particular responsibilities of a territory. A region hosting a significant proportion of the global population of a species bears increased responsibility for its conservation, even if the species is not formally threatened there. This ethical and strategic dimension enriches the reflection beyond mere quantitative criteria.

The issue of insufficient data remains a major challenge. Rather than blocking the assessment process, the DD category allows for the identification of knowledge gaps and the direction of research efforts. It also avoids underestimating threats due to a lack of data, a bias that has long affected freshwater ecosystems.

Prospects for the Coming Years

The IUCN World Conservation Congress, scheduled for October 2025, will guide conservation priorities for the next four years. Regional assessments will play a central role in this roadmap. The objective: to translate scientific knowledge into concrete solutions, restore degraded ecosystems, and reverse the curve of biodiversity decline.

The success of this ambition relies on the multiplication of rigorous and updated regional Red Lists. Each territory, whether national, provincial, or local, can contribute to this collective effort by applying the standardized IUCN methodology. Resources are accessible, tools are proven, and the ecological urgency is no longer debatable.

Freshwater landscapes perfectly illustrate this challenge. They host 10% of all known species on Earth and provide essential services: drinking water, livelihoods, flood control, climate change mitigation. Their protection is not just an environmental issue; it is a necessity for billions of people.

Conclusion

The IUCN Red List offers a proven methodology for transforming scientific observations into effective conservation actions. From rigorous quantitative criteria to operational recommendations, this practical guide enables regional and national actors to accurately assess extinction risks and adjust their strategies accordingly. At a time when a quarter of freshwater animals are threatened, each regional assessment becomes an act of collective responsibility. Sixty years after its creation, the Red List remains our best tool for understanding, measuring, and preserving the diversity of life on our planet.