Taxonomic Notes
Potamotrygon schuhmacheri is a species that is little represented in scientific collections (Rosa 1985). The type-locality of P. schuhmacheri is the Colastiné River (a branch of the Paraná River), in Santa Fe, Argentina (Castex 1964). It is a species that belongs to a group of stingrays with a pattern of reticulated dark pigment on the back (Carvalho et al. 2003). This fact is associated with misidentifications, where P. schuhmacheri is mistaken with other sympatric and syntopic species, such as P. histrix, P. falkneri, and even young individuals of P. brachyura. Potamotrygon schuhmacheri has also been considered a junior synonym of P. histrix, but a taxonomic review is needed. Potamotrygon schuhmacheri is sometimes referred to as P. schuemacheri and P. schühmacheri. This species name was considered an improper latinization due to the deletion of the second "h" in “schuhmacheri”, and this spelling was adopted by Rosa (1985) based on the first revisor principle, but is referred to as P. schuhmacheri by Carvalho et al. (2003) and Last et al. (2016). Lucifora et al. (2016) suggested that the species is rare, based only on the few existing records in the collections of the Museo Provincial de Ciencias Naturales “Florentino Ameghino” (Santa Fe, Argentina) and in the National Museum of Natural History (Washington, USA). Thus, efforts to obtain new specimens are necessary to confirm if this species is indeed rare (and even a valid species) or just subsampled.
Justification
The Rosette Freshwater Stingray (Potamotrygon schuemacheri) is a rare and poorly-known small (to 25 cm disc width) Neotropical freshwater stingray. It seems to have a patchy distribution along the Paraná-Paraguay River basin. There are few records and some uncertainty about its taxonomic validity still persists. Its fecundity, gestation period, and reproductive cycle remain unknown. The distribution range of this species overlaps areas subject to habitat degradation and anthropogenic impacts. This species is probably captured for the international ornamental aquarium trade and subsistence fishing can occur, as observed for most of its congeners; however, this is uncertain. Negative fishery is also considered a threat for this species. Since it is unknown if habitat quality and fishing are causing a population reduction, there is currently inadequate information available to assess the Rosette Freshwater Stingray beyond Data Deficient.
Geographic Range Information
The Rosette Freshwater Stingray occurs in Argentina, Brazil, and Paraguay. It is known from the Paraná-Paraguay River basin, mainly in the Paraná River and the Colastiné River, a branch of Paraná River (near Santa Fé), and Paraguay River (near Assunción) (Castex 1964, Rosa 1985, Garrone-Neto and Haddad 2010, Garrone-Neto et al. 2016). This species seems to be expanding its distribution range to areas where it did not originally occur, mainly to the Upper Paraná River (Garrone-Neto and Haddad 2010, Garrone-Neto et al. 2016), possibly due to the destruction of natural barriers by dams created to generate hydroelectric power, including the reservoir of the Itaipu Hydroelectric Plant (Garrone-Neto et al. 2014, D. Garrone-Neto, pers. comm. 2022). The Rosette Freshwater Stingray is possibly found in the upper Paraná and Paraguay River drainages (Castex 1964, Rosa 1985).
Population Information
There is no information available on the population size or trend of the species. There are few records in the literature and the available data basically deals with some taxonomic and occurrence aspects in the Paraná-Paraguay Basin. The population status of the Rosette Freshwater Stingray remains unknown. There is no evidence of population decline for this species, however, the region where this species occurs is subject to many anthropogenic impacts such as dams and habitat degradation. Thus, the population trend due to habitat quality and interactions with fisheries is unknown.
Habitat and Ecology Information
The few individuals available indicate that the Rosette Freshwater Stingray is a small species, with a maximum size of approximately 25 cm disc width (DW) (Lucifora et al. 2016). In Brazil, the species was collected on muddy substrates, close to marginal shallow waters (around 1 m depth) (Garrone Neto and Haddad Jr. 2010, Garrone-Neto et al. 2016). Castex (1964) reported that the holotype was collected during the flood season in the Colastiné River in Argentina.
Threats Information
As data on this species are very limited, the threats that can affect the Rosette Freshwater Stingray are not well known. Habitat loss and degradation related to agriculture, infrastructure development, and water pollution (from agriculture) seem to be the main potential threats (Charvet-Almeida and Almeida 2004). Moreover, in the Paraná-Paraguay Basin the construction of large hydroelectric plants in the past and, currently, the high number of small hydroelectric plants projects, have altered this river basin in several places (Garrone-Neto et al. 2016). Since the few records of the Rosette Freshwater Stingray are concentrated in densely populated areas, it is necessary to improve the understanding to which extent dams and other anthropogenic impacts, such as pollution and loss of marginal habitat, are directly affecting this species. Other threats are related to the fear that fishers and bathers have of negative interactions (stinging accidents) with Potamotrygon rays. This fear usually leads to negative fishery (tail mutilation, killing and discard), in an attempt to prevent accidents. Intrinsic factors associated with a relatively limited distribution range are a potential problem if severe environmental impacts persist.
Use and Trade Information
Although uses of the species are not known, targeting for the international ornamental aquarium trade and subsistence fishing may occur, as observed for most Rosette Freshwater Stingray congeners.
Conservation Actions Information
There are no species-specific conservation actions or monitoring for this species. The Potamotrygoninae subfamily (referred as Potamotrygonidae) was listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) Appendix III in 2017 mainly to improve trade data (CITES 2017). The Rosette Freshwater Stingray was not included in this listing as one of the priority species to be monitored (CITES 2017). The Rosette Freshwater Stingray was also not listed in the recent addition of Potamotrygon species under CITES Appendix II (CITES 2023). Further research is needed on population size and trends, and life history, and catch rates should be monitored.