One-quarter of freshwater fauna threatened with extinction

Abstract

Freshwater ecosystems are highly biodiverse¹ and important for livelihoods and economic development², but are under substantial stress³. To date, comprehensive global assessments of extinction risk have not included any speciose groups primarily living in freshwaters. Consequently, data from predominantly terrestrial tetrapods^4,5 are used to guide environmental policy⁶ and conservation prioritization⁷, whereas recent proposals for target setting in freshwaters use abiotic factors^8-13. However, there is evidence^14-17 that such data are insufficient to represent the needs of freshwater species and achieve biodiversity goals^18,19. Here we present the results of a multi-taxon global freshwater fauna assessment for The IUCN Red List of Threatened Species covering 23,496 decapod crustaceans, fishes and odonates, finding that one-quarter are threatened with extinction. Prevalent threats include pollution, dams and water extraction, agriculture and invasive species, with overharvesting also driving extinctions. We also examined the degree of surrogacy of both threatened tetrapods and freshwater abiotic factors (water stress and nitrogen) for threatened freshwater species. Threatened tetrapods are good surrogates when prioritizing sites to maximize rarity-weighted richness, but poorer when prioritizing based on the most range-restricted species. However, they are much better surrogates than abiotic factors, which perform worse than random. Thus, although global priority regions identified for tetrapod conservation are broadly reflective of those for freshwater faunas, given differences in key threats and habitats, meeting the needs of tetrapods cannot be assumed sufficient to conserve freshwater species at local scales.

Fig. 1. Patterns of extinction risk in tetrapods (combined) and freshwater species (decapod crustaceans, fishes and odonates; combined and individually).

The numbers above each column refer to the total numbers of species assessed and the best estimates of the proportion of species threatened (Methods). The black lines represent the best estimates of the proportion of species threatened. Red List categories are as follows: extinct (EX), extinct in the wild (EW), critically endangered (CR), endangered (EN), vulnerable (VU), data deficient (DD), near threatened (NT) and least concern (LC). Source data

Fig. 2. Proportion of threatened freshwater species, extinct freshwater species and threatened tetrapods.

a, Proportion of threatened freshwater species (decapod crustaceans, fishes and odonates; combined and individually), extinct freshwater species (combined) and threatened tetrapods (combined) affected by each threat. The darker cells indicate a greater proportion of species affected by the threat. Threats are not mutually exclusive. Threats are coded following the IUCN Threats Classification Scheme (version 3.3) and combined for presentation as follows (the value of the highest hierarchical level is indicated; all subsequent levels are included): pollution (9); dams and water management (7.2); agriculture (2.1, 2.2 and 2.3); invasive species and disease (8.1, 8.3, 8.4, 8.5 and 8.6); logging (5.2 and 5.3); urban development (1); hunting and fishing (5.1 and 5.4); energy production and mining (3); climate change and severe weather (11); human intrusions and disturbance (6); other ecosystem modifications (7.3); transportation (4); fire and fire suppression (7.1); problematic native species (8.2); aquaculture (2.4); and geological events (10). For the number of species: threatened freshwater species n = 4,190, extinct freshwater species n = 82, threatened decapods n = 472, threatened fishes n = 3,032, threatened odonates n = 686 and threatened tetrapods n = 7,112. b, Proportion of threatened freshwater species (decapod crustaceans, fishes and odonates; combined and individually) and extinct freshwater species (combined) using each wetland habitat. The darker cells indicate a greater proportion of species using the habitat. Habitats are not mutually exclusive. Habitats are coded following the IUCN Habitats Classification Scheme (version 3.1) as follows: permanent rivers (5.1); permanent lakes (5.5); seasonal rivers (5.2); permanent pools (5.7); bogs and marshes, among others (5.4); seasonal pools (5.8); springs and oases (5.9); karst (5.18); seasonal lakes (5.6); other wetlands (5.3, 5.10, 5.11 and 5.12); and saline, brackish or alkaline (5.14, 5.15, 5.16 and 5.17). For the number of species: threatened freshwater species n = 4,255, extinct freshwater species n = 100, threatened decapods n = 484, threatened fishes n = 3,071 and threatened odonates n = 700. In panels a,b, threatened species include those assessed as critically endangered (including those flagged as possibly extinct and possibly extinct in the wild), endangered or vulnerable. Extinct freshwater species include those assessed as extinct or extinct in the wild.

Fig. 3. Absolute richness of threatened freshwater species.

Threatened species are those assessed as critically endangered, endangered or vulnerable (including those flagged as possibly extinct and possibly extinct in the wild). The following distributions are included: presence refers to extant, probably extant or possibly extinct; origin denotes native, reintroduced or assisted colonization; and seasonality indicates resident, breeding, non-breeding or passage. The value of each cell is calculated as the count of threatened species with a mapped distribution overlapping the cell. Richness is shown using a 0.5 × 0.5 latitude–longitude grid and WGS84. World Bank Official Boundaries (licensed under a Creative Commons licence CC BY 4.0) were used as the base map. For absolute threatened species richness of tetrapods, see ref. .

Extended Data Fig. 1. Habitats used by threatened freshwater species (decapod crustaceans, fishes, and odonates; combined) and threatened tetrapods.

Threatened species include those assessed as Critically Endangered, Endangered, or Vulnerable (including those flagged as Possibly Extinct and Possibly Extinct in the Wild). Habitats are not mutually exclusive. Habitats are coded following the IUCN Habitats Classification Scheme (version 3.1) and combined for presentation as follows (value of highest hierarchical level is indicated, all subsequent levels are included): wetlands (5); forest (1); artificial (combined) (14, 15); marine (combined) (9, 10, 11, 12, 13); shrubland (3); grassland (4); rocky areas (6); savanna (2); caves & subterranean (7); and desert (8). The following habitats are not shown: introduced vegetation (16); other (17); and unknown (18). Number of species: threatened freshwater species n = 4,236; and threatened tetrapods n = 7,108.

Extended Data Fig. 2. Absolute richness of freshwater species for a) all freshwater species; b) Data Deficient freshwater species; and c) threatened freshwater species (excluding Critically Endangered (Possibly Extinct) and Critically Endangered (Possibly Extinct in the Wild) species).

The following distributions are included: Presence = Extant, Probably Extant, or Possibly Extinct; Origin = Native, Reintroduced, or Assisted Colonisation; and Seasonality = Resident, Breeding, Non-breeding, or Passage. The value of each cell is calculated as the count of species with a mapped distribution overlapping the cell. Richness shown using a 0.5 × 0.5 latitude-longitude grid and WGS84. World Bank Official Boundaries (licensed under a Creative Commons licence CC BY 4.0) were used as the base map.

Extended Data Fig. 3. Proportional richness of threatened freshwater species a) including Critically Endangered (Possibly Extinct) and Critically Endangered (Possibly Extinct in the Wild) species; and b) excluding Critically Endangered (Possibly Extinct) and Critically Endangered (Possibly Extinct in the Wild) species.

The following distributions are included: Presence = Extant, Probably Extant, or Possibly Extinct; Origin = Native, Reintroduced, or Assisted Colonisation; and Seasonality = Resident, Breeding, Non-breeding, or Passage. The value of each cell is calculated by its absolute threatened species richness divided by its absolute species richness. Richness shown using a 0.5 × 0.5 latitude-longitude grid and WGS84. World Bank Official Boundaries (licensed under a Creative Commons licence CC BY 4.0) were used as the base map.

Extended Data Fig. 4. Species Accumulation Index (SAI) values and curves from the surrogacy analysis, indicating the effectiveness of tetrapods (combined or individually) as surrogates for freshwater species (combined) targets.

Values and curves are shown for two alternative conservation strategies: a) maximises rarity-weighted richness, and b) maximises inclusion of the most range-restricted species. See Methods for a full explanation of each strategy. Surrogate effectiveness is measured using the Species Accumulation Index (SAI): values range from −∞ to 1, with 1 indicating perfect surrogacy, values between 1 and 0 indicating positive surrogacy, 0 indicating no surrogacy, and values less than 0 indicating negative surrogacy. In each panel, median SAI values are provided, with lower and upper confidence intervals in brackets. Blue lines are the optimal curves (accumulation of target diversity based on target priority areas); red lines are the surrogate curves (accumulation of target diversity based on surrogate priority areas); and grey lines are the random curves (accumulation of target diversity based on random selection of areas). Confidence intervals (95%, based on 100 randomisations) are shown in lighter shading around curves; most are too small to be visible.

Extended Data Fig. 5. Species Accumulation Index (SAI) values and curves from the surrogacy analysis, indicating the effectiveness of tetrapods (combined) surrogates for freshwater species (individually) targets.

Values and curves are shown for two alternative conservation strategies: a) maximises rarity-weighted richness, and b) maximises inclusion of the most range-restricted species. See Methods for a full explanation of each strategy. Surrogate effectiveness is measured using the Species Accumulation Index (SAI): values range from −∞ to 1, with 1 indicating perfect surrogacy, values between 1 and 0 indicating positive surrogacy, 0 indicating no surrogacy, and values less than 0 indicating negative surrogacy. In each panel, median SAI values are provided, with lower and upper confidence intervals in brackets. Blue lines are the optimal curves (accumulation of target diversity based on target priority areas); red lines are the surrogate curves (accumulation of target diversity based on surrogate priority areas); and grey lines are the random curves (accumulation of target diversity based on random selection of areas). Confidence intervals (95%, based on 100 randomisations) are shown in lighter shading around curves; most are too small to be visible.

Extended Data Fig. 6. Species Accumulation Index (SAI) values and curves from the surrogacy analysis, indicating the effectiveness of two abiotic factors as surrogates for freshwater species (combined) targets: a) water stress, and b) Nitrogen (as a proxy of eutrophication).

Values and curves are shown for two alternative conservation strategies: 1) maximises rarity-weighted richness, and 2) maximises inclusion of the most range-restricted species. See Methods for a full explanation of each strategies and values of water stress. Surrogate effectiveness is measured using the Species Accumulation Index (SAI): values range from −∞ to 1, with 1 indicating perfect surrogacy, values between 1 and 0 indicating positive surrogacy, 0 indicating no surrogacy, and values less than 0 indicating negative surrogacy. In each panel, median SAI values are provided, with lower and upper confidence intervals in brackets. Blue lines are the optimal curves (accumulation of target diversity based on target priority areas); red lines are the surrogate curves (accumulation of target diversity based on surrogate priority areas); and grey lines are the random curves (accumulation of target diversity based on random selection of areas). Confidence intervals (95%, based on 100 randomisations) shown in lighter shading around curves; most are too small to be visible.