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Potamotrygon brachyura

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES POTAMOTRYGONIDAE

Scientific Name: Potamotrygon brachyura
Species Authority: (Günther, 1880)
Common Name(s):
English Giant Freshwater Stingray
Synonym(s):
Trygon brachyurus Günther, 1880

Assessment Information [top]

Red List Category & Criteria: Data Deficient ver 3.1
Year Published: 2009
Date Assessed: 2003-06-24
Annotations:
Needs updating
Assessor(s): Charvet-Almeida, P., Soto, J.M.R. & Pinto de Almeida, M.
Reviewer(s): Kyne, P.M., Cavanagh, R.D. & Fowler, S.L. (Shark Red List Authority)
Justification:
The Giant Freshwater Stingray (Potamotrygon brachyura) is the largest species of the Potamotrygon genus; this freshwater stingray is probably endemic to the Paraná-Paraguay River drainages in southern South America. A moderately common but poorly known species. Its fecundity is relatively high compared with other potamotrygonids (up to 19 pups) but, in general, limited life history and population data are available. It is harpooned for food and also captured for the ornamental fish trade, especially juveniles. Given its limited distribution in areas subject to habitat degradation through various human activities further studies, monitoring and a revised assessment in the near future are highly recommended.

Geographic Range [top]

Range Description: South America inland waters: probably endemic to the Paraguay and lower Paraná river basins, it is found in Rio de la Plata, lower-mid Paraná River, mid Uruguay River and Paraguay River in Northeastern Argentina, western Brazil (States of Mato Grosso, Paraná and Rio Grande do Sul), central Paraguay and western Uruguay (Rosa 1985, Carvalho et al. 2003, Araújo et al. 2004, assessor's pers. obs.). Citations of this species for the Orinoco and Amazon drainages probably represent misidentifications (Rosa 1985, assessor's pers. obs.).
Countries:
Native:
Argentina; Brazil (Mato Grosso, Paraná, Rio Grande do Sul); Paraguay; Uruguay
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: The major concentration area for this species is apparently the middle Uruguay River, where it is considered relatively frequent (Soto pers. obs.).
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: Little is known about the habitat and ecology of this species but relative to information available on other potamotrygonid species the information on P. brachyura is significant. Castex and Maciel (1965) observed this species in very shallow waters and obtained most specimens from quiet waters of lagoons, brooks and streams in the region of Santa Fe, Argentina, during August and September 1962, when the Paraná River was at its lowest level, and during March and April in 1963 when water levels started to increase. They also mentioned that by early autumn, when water temperatures started to fall, this was the only species of river ray still found. The reproductive period of this species was indicated as commencing later in the year than P. motoro (pregnant individuals observed in January).

Achenbach and Achenbach (1976) found P. brachyura in all river systems in the mid Paraná River and this was the second most abundant potamotrygonid in their study. Captures took place mainly between mid-October and the beginning of November. During floods, specimens could be observed resting over vegetation, and fishermen took advantage of this behaviour to harpoon them.

An ovoviviparous species with gravid females usually over 40 cm DW. The highest number of births was observed during November and December, and the maximum litter size observed was 19 pups. Only the left ovary seems functional (Achenbach and Achenbach 1976).

According to Achenbach and Achenbach (1976), pups feed on plankton after birth. Juveniles complement their diet with small mollusks (Lamellibranches and Gastropods), crustaceans, larvae of aquatic insects, and fish (Loricariidae, Astyanax spp. and Pimelodella gracilis were recorded from adults).
Systems: Freshwater

Threats [top]

Major Threat(s): As with some other species of river stingray in the southern region of South America, the flesh of P. brachyura is particularly highly rated and this species is therefore called "raya fina" (fine ray) (Achenbach and Achenbach 1976) It is harpooned by fishermen when sighted resting in shallow water.

There is a small amount of fishing for the more attractively patterned juveniles to supply the ornamental fish trade. This species is illegally exported from Brazil but very limited information is available concerning this international trade. Due to its large size it is presumably not among the most commercialised species however it is still necessary to monitor the ornamental catches in order to determine trends and optimise management.

The major threats to the species are likely due to habitat degradation caused by the damming of the Paraná River system for navigation and hydroelectric plants, and the construction of many ports along the river (infrastructure development). Agriculture, livestock and various kinds of water pollution also affect the habitat of this species.

Expressive mortality close to "thermal stations" in Uruguay (generally in the winter months) require more specific studies (Soto pers. obs). These popular tourist sites (for recreation and health treatment) are natural thermal springs which are cleaned by flushing large volumes of hot water, resulting in mortality to river rays due to temperature shock.

Intrinsic factors, including restricted range, may also affect the threatened status of this species.

Conservation Actions [top]

Conservation Actions: Habitat maintenance and conservation are important measures for this species. The construction of hydroelectric and thermal stations should be controlled or restricted (not only to benefit this species but similar species and other wildlife in the area). Management plans, specific legislation and community management are also recommended in order to reduce and regulate sustainable use as a food resource and for the ornamental trade. Research actions and fishery monitoring are also required. Education and public awareness of potamotrygonids is essential due to the negative image of these species (often resulting in persecution due to fear of injury from the sting).

Citation: Charvet-Almeida, P., Soto, J.M.R. & Pinto de Almeida, M. 2009. Potamotrygon brachyura. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 26 July 2014.
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