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Rhinoptera bonasus

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES RHINOPTERIDAE

Scientific Name: Rhinoptera bonasus
Species Authority: (Mitchill, 1815)
Common Name(s):
English Cowfish, Cownose Ray, Skeete
French Mourine Américaine
Spanish Cara De Vaca, Gavilan Mancha, Gavilan Manchado, Mancha, Raya Gavilán
Taxonomic Notes: Originally, Raja bonasus Mitchill, 1815, this species has also been called Rhinoptera lalandii Müller & Henle, 1841 and Rhinoptera affinis Bleeker, 1863.

This species is sometimes confused with Rhinoptera brasiliensis, which can only be distinguished from R. bonasus by counting the series of toothplates. R. bonasus usually have seven series of plates in both jaws, while R. brasiliensis teeth are typically arranged in series of nine (Bigelow and Schroeder 1953). However, this distinction is not always well defined, as members of both species are sometimes found with fewer or more than the expected series in either jaw (Bigelow and Schroeder 1953, Schwartz 1990). While Gallo-da-Silva (1997) confirmed the distinction between the two species by providing a comparison of cranial anatomy, others have suspected that these two species are actually the same (Schwartz 1965, Schwartz 1990). This issue clearly requires a continued effort at taxonomic resolution.

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2006
Date Assessed: 2006-01-31
Assessor(s): Barker, A.S.
Reviewer(s): Kyne, P.M., Fowler, S.L. & Compagno, L.J.V. (Shark Red List Authority)
Justification:
A large (to 107 cm disc width) batoid of shallow marine and brackish waters of the western Atlantic distributed from the northern US to Brazil, including through the Gulf of Mexico. The schooling nature and inshore habitat of this species together with their relatively late maturity and low productivity (generally one young per litter) increases their susceptibility to overexploitation and will limit their ability to recover from population decline. This species is assumed to be highly migratory, but movement patterns are not well known and research into this area is required. Although there is currently no directed fishery for the cownose ray in the US, it has been suggested due to their reputation as a "pest" species to the shellfish industry. In US waters they are currently taken as bycatch in fisheries employing pound nets, haul seines and shrimp trawls, however, these activities do not pose a significant threat to the species at the present time and the population appears to be healthy. As such the species is assessed as Least Concern in the USA. However, if a fishery for cownose rays is ever established, it could be devastating to the population without proper monitoring. The species is assessed globally as Near Threatened due to heavy (and generally unregulated) fishing pressure on the inshore environment throughout large parts of Central and South America. Although no information is currently available on its contribution to artisanal fisheries in these regions, as a broadly distributed, migratory species inhabiting shallow coastal waters it is most certainly commonly taken either in directed catches or as bycatch. Rhinopterids are regularly landed around the world and heavy pressure on the inshore ecosystem is having negative impacts on congeners of R. bonasus, for example R. javanica throughout Asia and R. brasiliensis in Brazil. Similar adverse population trends are expected for R. bonasus and there is an urgent need to determine the current population status and catch levels.

Geographic Range [top]

Range Description: This species is found along continental shelves in warm temperate and tropical waters of the western Atlantic, from southern New England, USA to southern Brazil, including coastal waters of the Gulf of Mexico and parts of the Caribbean (whilst recorded from Cuba, apparently not confirmed from Jamaica, Hispaniola or the Lesser Antilles). It is known to frequent bays and estuaries of these areas, and has been reported as especially abundant in the Chesapeake Bay during summer months (Schwartz 1965, Smith and Merriner 1987). The exact southern limit of range in Brazil is uncertain due to confusion with the very similar R. brasiliensis.
Countries:
Native:
Belize; Brazil; Colombia; Costa Rica; Cuba; French Guiana; Guatemala; Guyana; Honduras; Mexico; Nicaragua; Panama; Suriname; Trinidad and Tobago; United States; Venezuela, Bolivarian Republic of
FAO Marine Fishing Areas:
Native:
Atlantic – northwest; Atlantic – southwest; Atlantic – western central
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: There are no existing population size estimates for this species, but they are common in parts of their range at certain times of the year. During suspected seasonal migrations, they often occur in groups of thousands of individuals (Clark 1963, Schwartz 1965, Smith and Merriner 1985, 1986, 1987, Rogers 1990). According to Schwartz (1990), the populations in the Western Atlantic (Southern New England to Brazil) and the Gulf of Mexico (Florida to the Yucatan Peninsula) are separate, but insufficient data exist to support this idea.
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: These rays occur in marine and brackish waters, often swimming into estuaries and bays. They have been reported in river portions of estuaries, at salinities as low as eight parts per thousand (Smith and Merriner 1987, A. Barker unpublished data). They are assumed to make mass schooling migrations, triggered at least in part by water temperature (Smith and Merriner 1985).

They are pelagic swimmers, benthic feeders, and are found at depths between 0 to 22 m (Fishbase.org). Reproduction is aplacental viviparous, with mature females giving birth usually to only one pup (although up to six embryos have been reported) (Bigelow and Schroeder 1953, Smith and Merriner 1986, Neer and Thompson 2005). There is confusion as to whether there are one or two annual reproductive events (Smith and Merriner 1986), although Neer and Thompson (2005) support a single annual reproductive event.

Primary prey includes benthic invertebrates, especially bivalve molluscs (Smith and Merriner 1985). Feeding activities by schooling rays have been implicated in extensive damage to seagrass (Orth 1975) and commercial shellfish beds (Smith and Merriner 1985, Peterson 2001).

Life history parameters
Age at maturity: 7 to 8 years (Chesapeake Bay; Smith and Merriner 1987), 4 to 5 years (N. Gulf of Mexico; Neer and Thompson 2005) (female); 5 to 6 years (Chesapeake Bay; Smith and Merriner 1987), 4 to 5 years (N. Gulf of Mexico; Neer and Thompson 2005) (male).
Size at maturity (disc width): 85 to 90 cm DW (Chesapeake Bay; Smith and Merriner 1986), 65 to 70 cm DW (Gulf of Mexico; A. Barker unpublished data, Neer and Thompson 2005) (female); 75 to 85 cm DW (Chesapeake Bay; Smith and Merriner 1986), 64 to 70 cm DW (Gulf of Mexico, A. Barker unpublished data, Neer and Thompson 2005) (male).
Longevity: ~13 years (Chesapeake Bay; Smith and Merriner 1987); 18+ years (females), 16+ years (males) (N. Gulf of Mexico; Neer and Thompson 2005).
Maximum size (disc width): 107 cm DW (Smith and Merriner 1987).
Size at birth: 25 to 40 cm DW (Smith and Merriner 1986, A. Barker unpublished data, Neer and Thompson 2005).
Average reproductive age (years): Unknown.
Gestation time: There is still speculation regarding gestation time, but it is 11 to 12 months if there is a single annual reproductive event, or 5 to 6 months if there are two (Chesapeake Bay, Smith and Merriner 1986). 11 to 12 months (N. Gulf of Mexico; Neer and Thompson 2005) (supporting a single annual reproductive event).
Reproductive periodicity: Females ovulate immediately after parturition, so periodicity is annual or biannual, depending on the resolution of the above issue..
Average annual fecundity or litter size: Typically gravid females have only 1 embryo, but there have been reports of up to 6 embryos within one female.
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
Systems: Marine

Threats [top]

Major Threat(s): There is currently no commercial fishery for this species in the Northwestern Atlantic, but there have been suggestions to establish one (Blankenship 1998) because of the damage that large feeding schools can do to shellfish and seagrass beds.

In the USA, present commercial fisheries for other species can pose a threat to cownose rays, which are caught as bycatch within pound nets, haul seines and shrimp trawls (J. Musick personal communication, G. Burgess personal communication). This species is quite hardy and is likely to survive netting and short amounts of time on the deck of fishing vessels. However, a venomous spine makes handling difficult and their reputation as a nuisance species may encourage persecution.

Although no information is currently available on its presence or contribution to artisanal fisheries throughout the species' Central and South American range, given its inshore habitat and the occurrence of fishing activities in coastal zones throughout its range it is most certainly commonly taken. In many regions of the species' southern range inshore fishing is intense and generally unregulated. For example, in parts of Brazil there is intensive fishing pressure by beach seine and benthic pair trawl fisheries and in southern Brazil these have had detrimental effects on the population of the congener R. brasiliensis which appears to be been extirpated from some areas.

Its inshore habitat, schooling behaviour and low productivity makes R. bonasus highly susceptible to overexploitation. Heavy (generally) fishing pressure on the inshore environment throughout large parts of Central and South America will most certainly be having an effect on R. bonasus, thus resulting in its global Near Threatened assessment.

Specific information on directed and/or bycatch levels are not available from Central and South America and the attainment of such data, as well as investigation into the current population status is of priority.

Conservation Actions [top]

Conservation Actions: There is no existing legislation involving this species. Elasmobranch fisheries are generally unmanaged throughout Central and South America. Attempts to monitor and regulate fisheries in these regions would greatly improve conservation of R. bonasus and other chondrichthyans. Monitoring (including species-specific catch details) of any directed elasmobranch landings and bycatch in Central and South America are necessary to provide valuable information on the biology and population status of these rays. Fishery-independent surveys of this and other elasmobranchs are necessary to provide estimates of abundance and biomass. Due to the transient nature of this schooling ray, coordinated national and international efforts are necessary to adequately assess movements, abundance, and fishery impacts.

Further research required includes an extensive tracking study to better estimate population size and movement patterns, and a focus on obtaining improved life history data from across the species? range, and the characterization of habitat use and potential nursery areas. Furthermore, direct estimates of fishing and natural mortality are critical for assessing fisheries impacts on a particular species.

The development and implementation of management plans (national and/or regional e.g., under the FAO International Plan of Action for the Conservation and Management of Sharks: IPOA?Sharks) are required to facilitate the conservation and sustainable management of all chondrichthyan species in the region. See Anon. (2004) for an update of progress made by nations in the range of R. bonasus.

Citation: Barker, A.S. 2006. Rhinoptera bonasus. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 01 August 2014.
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