true

ISRA FACTSHEETS

SOUTH AMERICAN INLAND WATERS

ISRA FACTSHEETS

SOUTH AMERICAN INLAND WATERS

Queguay-Rio Negro ISRA

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Queguay-Rio Negro ISRA

Queguay-Rio Negro

Summary

Queguay-Rio Negro is located in Uruguay and Argentina. It is situated in the middle section of the Uruguay River within the Rio de la Plata basin. This area extends from La Concordia, including the lower part of Rio Negro that flows into Uruguay River, to Queguay Islands close to the mouth of the Queguay River, and some areas are characterised by an extensive sandy substrate. This area partially overlaps with four Key Biodiversity Areas, one Ramsar Site, and one protected area. Within this area there are: threatened species and reproductive areas (Giant Freshwater Stingray Potamotrygon brachyura).

Queguay-Rio Negro

Queguay-Rio Negro

DESCRIPTION OF HABITAT

Queguay-Rio Negro is a transboundary area located between Uruguay and Argentina. It is situated in the middle section of the Uruguay River within the Rio de la Plata basin. This area extends from La Concordia, including the lower part of Rio Negro that flows into Uruguay River, to Queguay Islands close to the mouth of the Queguay River characterised by an extensive sandy area. The Uruguay River is the second-largest tributary of the Rio de la Plata in terms of discharge (Graca et al. 2025). It has a length of 1,800 km, from its headwaters in Serra do Mar in Brazil to the Rio de La Plata (Graca et al. 2025). The hydrological regime of the river is unseasonal and highly irregular (Graca et al. 2025). The middle and lower Uruguay basin include floodplains, grasslands, savanna, and scrubland (Graca et al. 2025).

This area partially overlaps with four Key Biodiversity Areas: Pastizales y Esteros del Bajo Río Negro, Ñandubaysal-El Potrero, Pastizales de Lorenzo Geyres y Quebracho, and Perdices (KBA 2025). It also overlaps with one Ramsar Site (Palmar Yatay; Ramsar 2025), and one protected area (Esteros de Farrapos e Islas del Río Uruguay; UNEP-WCMC 2025).

This Important Shark and Ray Area is benthic and is delineated from surface waters (0 m) to 10 m based on the bathymetry of the area.

CRITERION A

VULNERABILITY

One Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened Species regularly occurs in the area. This is the Vulnerable Giant Freshwater Stingray (Lucifora et al. submitted).

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

Queguay-Rio Negro is an important reproductive area for one ray species.

Giant Freshwater Stingray has been historically regularly documented in this area (Oddone et al. 2008, 2012). In the 1980s, an aggregation of 20–30 Giant Freshwater Stingrays was documented in this region, reported to be for mating purposes (A Milessi pers. obs. 2025). Additionally, anecdotal reports from local fishers suggest that large numbers of Giant Freshwater Stingrays regularly aggregate across the area’s extensive sandy substrates.

Between 2019–2024, informal interviews with seven artisanal and sport fishers revealed that this species is regularly captured in the area, primarily during the austral summer and spring (A Milessi pers. obs. 2025). Traditional ecological knowledge, passed down through two generations of fishers, indicates that pregnant females and near-term aborted embryos are frequently observed during these months, giving birth in shallow warmer waters in this area (I González unpubl. data 2025). A pregnant female has been also recorded giving birth to two neonates in this area (Castello & Jones 2016).

This species has also been recorded in fishery surveys conducted between 2005–2019 (López-Rodríguez et al. 2019; Vidal et al. 2021). Notably, this is the only known location where reproductive activity has been reported across its entire distribution range (from northeastern Argentina, south central-west and south Brazil, Paraguay, Uruguay, and possibly in easternmost Bolivia; Lucifora et al. submitted).

Queguay-Rio Negro

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