The mystery of Styracura schmardae stingrays from the Brazilian Amazon coast

The Brazilian Amazon coast (BAC) is a large area comprising the states of Amapá, Pará and Maranhão, which suffers the influence of countless estuaries, voluminous rivers and dense mangrove forests. The coastline presents certain sui generis characteristics, such as a macrotidal regime with amplitudes reaching up to 7.5 m, a tropical weather with average temperatures above 27 °C throughout the year and a rainy season with a mean precipitation rate of about 2000 mm/year [1]. Due to the particularities of this environment, the local ichthyofauna displays significant physiological plasticity, and many species present adaptations to significant salinity variations [2], a striking condition of BAC estuarine systems due, mainly to the local rain volume [3]. However, ecology assessments usually focus on the importance of abundant species, rather than the role of rare species in various types of environments. Nevertheless, rare species presents restricted and specific relationships to certain types of environments or correspond to equally neglected endemic species [4].

In this context, the Atlantic Chupare stingray Styracura schmardae is considered a rare species throughout its distribution area, which ranges from the Gulf of Campeche, in Mexico, to the state of Ceará, in Brazil, including the Lesser and Greater [5,6]. Currently, the Styracura genus, plays an important role as a sister group of the Potamotrygoninae subfamily, composed by the freshwater rays of South America, based on morphological and molecular analyses [7,8,9]. Even though the Styracura genus was recently relocated, on a provisional basis, from the Dasyatidae family to the Potamotrygonidae family, it is possible that this genus may belong to a family of its own, since it inhabits in marine environments [9].

In Brazil, occurrence records are available only for S. schmardae [6,10-14], with no publications on its biology and ecology, except for information available in gray literature. This lack of information appears to occur globally, as this species is currently classified as Data Deficient (DD) by the International Union for Conservation of Nature’s Red List (IUCN) [5]. Thus, a great mystery surrounds S. schmardae, since a BAC population is known, but specifically, where does it reside? Important ecological information on this species is being collected in the central Bahamas, located in the Northwest Atlantic Ocean [15], probably comprising a distinct population from the BAC, considering that the migration process of these demersal rays is difficult to occur, since individuals would have to find shallow migration routes or cross significantly deep locations.

The reduced number of records in Brazil is due not only to the southern limit of S. schmardae’s distribution, but also due to its environmental specificities, considering that records are available only for estuarine environments undergoing significant influence from the mouths of the Amazon rivers, supporting low salinity values [12]. In addition, few fishers in the region know how to fish this animal, which requires specific knowledge comprising type of bait and hook, as well as location, moon phase and tidal dynamics. However, it is almost common knowledge that S. schmardae offers a higher risk for fisher accidents, as it is the only stingray that swims towards humans when caught in artisanal fishing (Palmeira-Nunes, unpublished data). This behavior led the species to be popularly known as Tatá in the state of Pará, an onomatopoeia in Portuguese for such a swimming movement.

In addition to its rare occurrences and restricted habitats, another mystery comprises adult specimen records, since, with the exception of a 2000 mm Disk Width (DW) observed in a specimen captured in Venezuela [16], all other records are for immature animals. Where are the adults of this species? Obviously, it is much more difficult to transport an adult individual belonging to a large species to an ichthyological collection than a young one, considering that S. schmardae appears to reach maturity at ~ 1000 mm DW (Palmeira-Nunes, unpublished data). However, no records are available, even considering current tools that allow for the cataloguing of live or freshly caught animals. In addition, little is known about the ecology of registered juvenile specimens, although they are indeed captured and consumed [5].

The series of unpublished studies from the central Bahamas will certainly shed new light on the population structure of S. schmardae in the Caribbean, since that is the largest population registered for this species until today [15]. However, a significant knowledge gap in this regard still remains for the BAC, exactly where the closest populations to the sister group restricted to the freshwater environment would be. We encourage researchers in the region to publish ecological data on this species, even if scarce, or to seek a network of contacts so that this puzzle may begin to be solved.

1. Souza Filho PWM (2005) Costa de manguezais de macromaré da Amazônia: Cenários morfológicos, mapeamento e quantificação de áreas usando dados de sensores remotos. Revista Brasileira de Geofísica 23: 427-435.
2. Barthem R (1985) Ocorrência, distribuição e biologia dos peixes da baía de Marajó, estuário amazô Boletim do Museu Paraense Emilio Goeldi. Série Zoologia 2: 49-69.
3. Cervigón F (1985) La Ictiofauna de las Aguas Costeiras Estuarinas del Delta del Rio Orinoco en la Costa Atlántica Occidental, Caribe. In: Yáñez AA (Ed.), Fish community ecology in estuaries and coastal lagoons: Towards an ecosystem integration. Mexico, 5: 57-78.
4. Wosnick N, Palmeira ARO, Nunes JLS (2019) E-letter-pinocchioland: The role of the Brazilian Amazonian coast in elasmobranch conservation. Science 334: 1.
5. Charvet AP, Almeida MP (2006) Himantura schmardae. The IUCN Red List of Threatened Species.
6. Jucá Queiroz B, Santander N, Medeiros J, Nascimento RS, Furtado NFCP, et al. (2008) Cartilaginous fishes (class Chondrichthyes) off Ceará State, Brazil. Western equatorial atlantic-an update. Arquivos de Ciências do Mar 41(2): 73-81.
7. Carvalho M, Loboda TS, Silva JPCB (2016) A new subfamily, Styracurinae, and new genus, Styracura, for Himantura schmardae (Werner, 1904) and Himantura pacifica (Beebe & Tee-Van, 1941) (Chondrichthyes: Myliobatiformes). Zootaxa 4175(3): 201-221.
8. Lovejoy NR, Birminghan E, Martin AP (1998) South American rays came in with the sea. Nature 396: 421-422.
9. Last PR, White WT, Carvalho MR, Séret B, Stehmann MFW, et al. (2016) Rays of the world. CSIRO Publishing, Melbourne.
10. Camargo M, Isaac V (2001) Os peixes estuarinos da região norte do Brasil: Lista de espécies e considerações sobre sua distribuição geográ Boletim do Museu Paraense Emílio Goeldi, Nova Serie, Zoologia 17(2): 133-157.
11. Gomes UL, Gadig OBF (2003) Família Somniosidae. In: Menezes NA, Buckup PA, Figueiredo JL, Moura RL (Eds.), Catálogo das Espécies de Peixes Marinhos do Brasil. São Paulo, Brazil p. 160.
12. Almeida MP, Charvet A, Rincon G, Barthem R (2008) Occurrence report of Himantura schmardae (Chondrichthyes: Dasyatidae) off northern Brazil. Arquivos de Ciências do Mar 41(2): 90-94.
13. Rosa RS, Gadig OBF (2014) Diversidade dos Chondrichthyes marinhos no Brasil. Arquivos de Zoologia 45: 89-104.
14. Jimenez E, Lima D, Amaral M, França T, Costa M, et al. (2017) Peixes da zona costeira do Parque Nacional do Cabo Orange, estuário amazônico, Amapá, Brasil. Macapá 90.
15. O Shea R, Ward CRE, Brooks EJ (2017) Range extension in styracura (= Himantura) schmardae (Caribbean Whiptail Stingray) from the Bahamas. Caribbean Naturalist 3(8): 1-388.
16. Cervigón F, Cipriani R, Fischer W, Garibaldi L, Hendrickx M, et al. (1994) Características generales de la ictiofauna. In: Claro R (Ed.), Ecología de los peces marinos de Cuba, pp. 55-70.