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Rhinoptera brasiliensis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES RHINOPTERIDAE

Scientific Name: Rhinoptera brasiliensis
Species Authority: Müller, 1836
Common Name(s):
English Brazilian Cownose Ray
Taxonomic Notes: Bigelow and Schroeder (1953) provide good descriptions of the two species R. bonasus and R. brasiliensis from Brazilian material but admitted at the same time that the two forms may not be separate species. The name R. brasiliensis was not used again until a few years ago. Figueiredo (1977) cites only R. bonasus for Southwest Brazil and this may be the reason why subsequent authors assigned catches of Rhinoptera from this area to R. bonasus.

However Gallo-da-Silva et al. (1997 in Menni and Stehmann 2000) confirmed the existence of both species off Rio de Janeiro, and all three specimens of Rhinoptera collected off Rio Grande do Sul in the 1980s were R. brasiliensis (Soto unpub. data).

The two species differ in the size at birth. According to data listed by Bigelow and Schroeder (1953), R. brasiliensis has a broader mouth and greater distances between nostrils and between spiracles than R. bonasus, and this corresponds with the difference between the two species in the tooth plate conformation, brasiliensis having three central rows of broad teeth and bonasus only one such row.

Assessment Information [top]

Red List Category & Criteria: Endangered A2abcd+3bcd+4abcd; B1ab(i,iii,v) ver 3.1
Year Published: 2004
Date Assessed: 2004-04-30
Assessor(s): Vooren, C.M. & Lamónaca, A.F.
Reviewer(s): Musick, J.A., Kyne, P.M., Cavanagh, R.D. & Fowler, S.L. (Shark Red List Authority)
Justification:
Rhinoptera brasiliensis is an inshore endemic cownose ray restricted to about 1,800 km of coastline between Rio de Janeiro and Rio Grande do Sul States in Brazil. The species is threatened by intense fishing activities throughout its restricted area of shallow coastal habitat. It is viviparous with only one embryo per litter, and as such is highly vulnerable to recruitment overfishing. In the southernmost 700 km of its distribution, off Rio Grande do Sul, the species occurred as a summer migrant in coastal waters at depths of <20 m, where it was caught and discarded in large numbers during the 1980s by the summer beach seine fishery, with catches of up to 330 individuals in a single haul. Fishing with bottom trawl has been intense in this southern area from the 1980s onwards, although the beach seine fishery is now minor due to serious catch declines. In summer 2002/2003, during three months of surveying the shore-based fishery, the species was no longer caught. It is suspected that the species has been extirpated by intensive fishing in the restricted area of its southern summer habitat and/or by fishing further north in the area from which come the summer migrants. The present situation of R. brasiliensis in the central and northern parts of its range is not known, however, fishing is intense throughout the range and declines in those areas are inferred. Declines are likely to continue as fishing proceeds without restriction. Its restricted distribution, very low fecundity, apparent extirpation from the southern part of its range and intensive fishing across its entire range warrant at least an Endangered assessment. It may prove to be Critically Endangered with further surveys, which are a priority.

Geographic Range [top]

Range Description: This endemic species occurs in a restricted area of the Southwest Atlantic: on the continental shelf of Brazil between Rio de Janeiro and Rio Grande do Sul (23°S to 34°S, an area of about 1,800 km of coastline) (Bigelow and Schroeder 1953, Menni and Stehmann 2000, Soto unpublished records off Rio Grande do Sul).

The species occurs sympatrically with R. bonasus from Rio de Janeiro to Santa Catarina State (Gallo-da-Silva et al. 1997 in Menni and Stehmann 2000, Soto unpubl. data). A reported high abundance of Rhinoptera rays off Paraná State (Barletta and Correa 1989 in Menni and Stehmann 2000), in the centre of the distribution of R. brasiliensis, may refer to either or both species of Rhinoptera. All three specimens of Rhinoptera collected off Rio Grande do Sul on three different occasions during the 1980s were R. brasiliensis (Soto unpubl. data). Evidence now suggests that the large summer catches of Rhinoptera off Rio Grande do Sul in the 1980s (Vooren and Lamónaca unpubl. data) were of R. brasiliensis, where the species occurred as a summer migrant in coastal waters at depths of <20 m (Vooren 1997, Soto, unpublished), and this is the only area to have recorded a high abundance of this species.
Countries:
Native:
Brazil (Rio de Janeiro, Rio Grande do Sul)
FAO Marine Fishing Areas:
Native:
Atlantic – southwest
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Sizes in beach seine catches in Rio Grande do Sul in the summer of 1982 to 1985 ranged from 78 to 91 cm disc width (DW) in males, and from 77 to 102 cm DW in females. A female of 102 cm DW was gravid. Three January embryos were 26 to 37 cm DW (Vooren and Lamónaca, unpubl. data). There are no records of catches of neonates off Rio Grande do Sul, therefore birth may take place further north. Size at birth is about 43 to 48 cm DW (Bigelow and Schroeder 1953), larger than that of R. bonasus, which is 40 cm DW (Smith and Merriner 1986). Gravid females contained one embryo only, as also observed in R. bonasus by Smith and Merriner (1986). The breeding cycle of females may be biennial, although specific information is not available.

On the coast of Rio Grande do Sul the species occurs during summer only, in shallow coastal waters over smooth sandy bottom at depths of less than 10 m and sporadically between 10 to 20 m (Vooren 1997). Bottom temperature at those depths is about 22°C in January and decreases to about 13°C in August (Haimovici et al. 1996). The summer migration of the species may be related to this seasonal temperature cycle.

Stomach contents from specimens from Rio Grande do Sul consisted of mollusc flesh mixed with numerous shell fragments with size of the order of 0.5 mm.
Systems: Marine

Threats [top]

Major Threat(s): The intensive fisheries by beach seine and pair trawl in the coastal habitat of the species is the major threat to the species. This ray used to be discarded by the beach seine fishery in the 1980s and has not been seen in commercial trawl landings (probably also discarded). Due to its low fecundity of one embryo only per litter, this viviparous ray is susceptible to recruitment overfishing.

In the southernmost 700 km of its distribution, off Rio Grande do Sul, the species occurred in the 1980s as a summer migrant in shallow coastal waters at depths of less than 20 m (Vooren 1997, a reference to R. bonasus but now presumed to refer to R. brasiliensis from identification of specimens by Soto, unpublished). In that area, between 1982-1985 the species was caught and discarded in large numbers by the summer beach seine fishery, with catches of up to 330 individuals in a single seine haul and of a total of 1,711 individuals in a series of eight hauls along 130 km of coastline on a single day in January 1985 (Vooren, unpubl. data). Catches included gravid females with mid-term embryos. Fishing by bottom trawl has been intense in the southern area of the species' range from 1980 onwards, although in recent years the beach seine fishery, important in the 1980s, is now minor due to ever declining catches. In summer 2002/2003, during three months of survey of the shore-based fishery, the species was no longer caught, although other rays (Myliobatis spp., Rhinobatos spp.) were still taken (Vooren and Lamónaca, unpubl. data of Project SALVAR).

Bigelow and Schroeder (1953) state that numbers of R. bonasus varied greatly between years at certain localities, with incursions of large schools occurring irregularly. This does not seem to be the case with R. brasiliensis in the 1980s, off Rio Grande do Sul. The apparent disappearance of the species here occurred after two decades of intense fishing in its coastal habitat. It is suspected that in the southern part of its range the species has been extirpated by intensive fishing in the restricted area of its summer habitat and/or by fishing further north in the area from which come the southern summer migrants. During the 1980s, rays of the genus Rhinoptera made up 8% of catches of the coastal elasmobranch fishery of Paraná State, in the centre of the geographical range of R. brasiliensis (Barletta and Correa 1989 in Menni and Stehmann 2000). The present situation of the stocks of R. brasiliensis in the central and northern parts of its range is not known, however, fishing in these areas is also intense and declines are inferred.

Conservation Actions [top]

Conservation Actions: No conservation measures have been undertaken. Surveys of the northern and central parts of the species' range are required to obtain population estimates and information on critical habitat. Closed areas with effective enforcement are vital to the survival of this species.

Citation: Vooren, C.M. & Lamónaca, A.F. 2004. Rhinoptera brasiliensis. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 18 December 2014.
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