Freshwater megafauna diversity: Patterns, status and threats

Abstract

Aim Freshwater megafauna remain underrepresented in research and conservation, despite a disproportionately high risk of extinction due to multiple human threats. Therefore, our aims are threefold; (i) identify global patterns of freshwater megafauna richness and endemism, (ii) assess the conservation status of freshwater megafauna and (iii) demonstrate spatial and temporal patterns of human pressure throughout their distribution ranges. Location Global. Methods We identified 207 extant freshwater megafauna species, based on a 30 kg weight threshold, and mapped their distributions using HydroBASINS subcatchments (level 8). Information on conservation status and population trends for each species was extracted from the IUCN Red List website. We investigated human impacts on freshwater megafauna in space and time by examining spatial congruence between their distributions and human pressures, described by the Incident Biodiversity Threat Index and Temporal Human Pressure Index. Results Freshwater megafauna occur in 76% of the world’s main river basins (level 3 HydroBASINS), with species richness peaking in the Amazon, Congo, Orinoco, Mekong and Ganges‐Brahmaputra basins. Freshwater megafauna are more threatened than their smaller counterparts within the specific taxonomic groups (i.e., fishes, mammals, reptiles and amphibians). Out of the 93 freshwater megafauna species with known population trends, 71% are in decline. Meanwhile, IUCN Red List assessments reported insufficient or outdated data for 43% of all freshwater megafauna species. Since the early 1990s, human pressure has increased throughout 63% of their distribution ranges, with particularly intense impacts occurring in the Mekong and Ganges‐Brahmaputra basins. Main conclusions Freshwater megafauna species are threatened globally, with intense and increasing human pressures occurring in many of their biodiversity hotspots. We call for research and conservation actions for freshwater megafauna, as they are highly sensitive to present and future pressures including a massive boom in hydropower dam construction in their biodiversity hotspots.

Biogeographic freshwater fish pattern legacy revealed despite rapid socio‐economic changes in China

“…Downward trends in the Red List Index and Living Planet Index suggest that key Aichi targets (i.e., targets, 2-4, 6-12, 14) are not on track to be met by 2020 (Convention on Biological Diversity, 2011;Gozlan, Karimov, Zadereev, Kuznetsova, & Brucet, 2019). Drivers regularly identified as playing a key role in these declines are habitat destruction, climate change and introduction of non-native species (Erős, Takács, Specziár, Schmera, & Sály, 2017;He et al, 2018;Martinuzzi et al, 2014;Reid et al, 2018;Toussaint et al, 2018). Nevertheless, detangling the effects of historical and contemporary determinants underpinning large-scale patterns of freshwater fish diversity and assemblage patterns is central to conservation strategies (Hoeinghaus, Winemiller, & Birnbaum, 2007;Jackson, Peres-Neto, & Olden, 2001;Kuczynski, Legendre, & Grenouillet, 2018).…”

Isotopes in teeth and a cryptic population of coastal freshwater seals

“…; He et al. ). Small and large hydropower dams are proliferating across the globe driving habitat fragmentation and changes to natural flow regimes with little consideration of consequences for aquatic mobile species, particularly mammals (Sabo et al.…”

“…Coastal marine, estuarine, and freshwater mammals are threatened globally (Pompa et al 2011). In particular, species and populations that migrate between estuarine and freshwater habitats, or that are freshwater dependent, include some of the most endangered mammals worldwide (He et al 2018). At least 1 extinction has occurred during the last decade (the Yangtze River dolphin [Lipotes vexillifer]) (Turvey et al 2007).…”

“…At least 1 extinction has occurred during the last decade (the Yangtze River dolphin [Lipotes vexillifer]) (Turvey et al 2007). Major threats to their persistence are directly due to human activity (Veron et al 2008;He et al 2018). Small and large hydropower dams are proliferating across the globe driving habitat fragmentation and changes to natural flow regimes with little consideration of consequences for aquatic mobile species, particularly mammals (Sabo et al 2017;Couto & Olden 2018).…”

Put freshwater megafauna on the table before they are eaten to extinction

“…() have pointed out that despite being listed on the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) appendices, freshwater megafauna are often illegally harvested for their eggs, meat, and skin. Meanwhile, they are also subject to intense and increasing threats including habitat degradation, dam construction, pollution, and biological invasion (He et al., ). However, current conservation actions do not reflect these conditions.…”