Pacific Cownose Rays, Rhinoptera steindachneri
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Description & Behavior
A common stingray, Pacific cownose rays, Rhinoptera steindachneri (Evermann and Jenkins, 1891), are members of the Family Myliobatidae or eagle rays and are also called golden cownose or hawk rays. Pacific cownose rays have a subrostral (below the front edge) lobe with a median notch. They have a single dorsal fin near the base of their long whip-like tail, and one or two stingers at the base of their tail. They are dark brown or golden on their dorsal (upper) sides with a creamy white ventrum or underside. Maximum width 90 cm; reef-associated; marine; depth range 0-30 m. Often observed in small groups and sometimes in large schools.
World Range & Habitat
This is the only species in this genus known in the Eastern Pacific: Gulf of California to Peru and the Galapagos Islands. Found over soft bottoms, near rocky or coral reefs and reef drop-offs. Occasionally found near the surface and can jump out of the water. Often in schools, sometimes associated with Aetobatus narinari, spotted eagle rays.
Feeding Behavior (Ecology)
Feeds on benthic crustaceans and mollusks. The soft subrostral fins are used to probe the substrate in search of bivalve prey and may serve to detect water expelled from a clam's siphon or the weak bioelectric field generated by a bivalve. To excavate their prey, they dig deep depressions up to 40 cm in depth in bottom sediment by flapping the pectoral fins and by sucking sediment through the mouth and expelling it out of the gill slits. The flat tooth plates, present on both jaws, are used to grind their hard shelled prey.
Pacific cownose rays, Rhinoptera steindachneri, are viviparous, the newborn resemble adults.
Conservation Status & Comments
Pacific cownose rays are harmless to humans.
IUCN Red List Status: Near Threatened (NT):
"Justification: Rhinoptera steindachneri is the only representative of its family known from the eastern Pacific. Little is known of the species' ecology yet it is one of the primary components of artisanal elasmobranch fisheries in the Gulf of California and the southern Pacific coast of the Baja peninsula (México). As a broadly distributed, migratory species inhabiting shallow coastal waters, it is likely an important component of artisanal fisheries throughout its range. The extent of movements throughout the eastern Pacific coast, longevity, growth rates, population structure, and age at maturity are unknown. Both sexes mature at similar sizes that are approximately 70% of their maximum size, suggesting that the species may have a relatively late age at maturity. The reproductive strategy of producing a single pup following an extended 10-12 month gestation period indicates that the species has a low productivity and is likely to be highly susceptible to overexploitation. Due to such low fecundity, fishing pressure and its important contribution to artisanal fisheries, R. steindachneri is considered to be Near Threatened throughout its range. An assessment of the species' current population status and monitoring of catches throughout its range is of priority.
Major Threat(s): Directed artisanal elasmobranch fisheries. Rhinoptera steindachneri is one of the most common batoid species landed in both the northern Gulf of California (GOC) and Bahía Almejas, Baja California Sur, México, where it is taken almost exclusively with bottom set gillnets, but may be landed in nearshore surface gillnets and longlines as well (Bizzarro et al. submitted, Notarbartolo di Sciara 1987). In the northern GOC from 1998?1999, R. steindachneri was most frequently observed in summer landings (11.4% of catch, CPUE=8.0 individuals/vessel/trip) and was rarely noted in winter (0.1%, CPUE=0.1). In Bahía Almejas from 1998?2000, it was more abundant in August (5.15%) than in June landings (0.30%), a trend also evident in CPUE (August=1.13, June=0.13). The mean size of female R. steindachneri captured in the GOC was 64.4 + 11.8 cm DW (mean and SD) whereas males averaged 64.2 + 14.0 cm DW (Bizzarro et al. submitted).
Also taken as incidental catch among trawl (especially shrimp trawlers) and other artisanal fisheries using gillnets and longlines in México. No information is currently available on its presence or contribution to artisanal fisheries throughout the rest of its range, however, given its inshore habitat and the occurrence of fishing activities in coastal zones throughout its range it is most certainly commonly taken.
Habitat modification. Many embayments and estuaries in north-west Pacific México are being modified to accommodate shrimp farming. Since this species uses these areas for feeding and reproduction, this could have a detrimental impact on its abundance in affected areas.
Conservation Actions: Rhinoptera steindachneri fisheries are generally unmanaged throughout the species range. In México, a moratorium on the issue of elasmobranch fishing permits was enacted in 1993, but no formal management plan has been implemented. However, legislation is currently being developed in México to establish national elasmobranch fishery management. Elasmobranch fisheries are generally unmanaged throughout Central and South America. Attempts to monitor and regulate fisheries in the eastern tropical Pacific would greatly improve conservation of R. steindachneri and other chondrichthyans.
Elasmobranch landings reported from México and Central America typically lack species specific details. Most often, all batoids are often simply termed "manta raya" collectively. Improved clarity in catch records would provide an essential basis for detecting fishery trends and are much needed throughout the species' range. Expanded monitoring of directed elasmobranch landings and bycatch in México, 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.
In addition to species-specific catch details, life history information including age, growth, longevity, movement patterns, habitat use, potential nursery areas, diet, and further reproductive studies are necessary to develop effective conservation actions for R. steindachneri. Direct estimates of fishing and natural mortality are critical for assessing fisheries impacts on a particular species. Tagging, tracking, and genetic studies are essential for determining the population structure, movement patterns, and possible subpopulations throughout the species' range.
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. steindachneri."
References & Further Research
Research Rhinoptera steindachneri » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
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