GOLDEN COWNOSE RAY
RHINOPTERA STEINDACHNERI EVERMANN & JENKINS, 1892
FAMILY RHINOPTERIDAE (COWNOSE RAYS)
Identification: A diamond-shaped ray with a head distinctly protruding from the disc. The anterior face of the cranium is concave with a bilobed subrostral fin. Width of the disc is about 1.7-1.8 times its length. The tail is extremely long and slender, about 1.2-1.6 times the disc length, with one or two rather small, serrated spines at the base. Coloration is uniformly pale yellowish to brown dorsally, white ventrally.
Size: Maximum size is 105 cm disc width (DW) for females. Males are slightly smaller, with a maximum-recorded size of 96 cm DW. Size records were derived from Bahía Almejas, on the Pacific coast of Baja California Sur, Mexico. Specimens from the Gulf of California reach smaller maximum sizes (98 cm DW, females; 89 cm DW, males).
Distribution: This species ranges from Bahia de Sebastian Vizcaino, central Baja California, to the Gulf of California and south to Peru, including the Galapagos Islands.
Habitat: This stingray inhabits nearshore and inshore waters to depths of approximately 30 m and can be found throughout the water column. It is usually associated with sandy substrates but also occurs near rock or coral reefs, often near the reef dropoffs. A transient, highly mobile species it often forms large schools or moves in loose aggregations. The movements of this stingray, like those of congeneric species, may be related to water temperature, as it tends to migrate northward in the Gulf of California during the spring and south in the autumn.
Biology: The reproductive mode of this species is aplacental viviparity. Females nourish young initially by means of a yolksac and later supplement this energy source with protein-rich uterine excretions termed hisotrophe. Only a single ovary is functional. Median size at 50% maturity for Gulf of California specimens is similar for females (70.2 cm DW) and males (69.9 cm DW). Fecundity is one offspring per female, with parturition estimated to occur from late June-August. Size at birth is estimated at 38-45 cm DW after a gestation period of approximately 11-12 months. Courtship and fertilization follow shortly after parturition. This species possesses plate-like teeth and appears to be primarily durophagous. Based on limited information, the diet consists of bivalves and tube-dwelling polychaetes. Individuals of this species from the Pacific coast of Baja California Sur reach greater maximum overall and embryo sizes than those from the Gulf of California.
General interest: This is one of the most abundant species landed in artisanal elasmobranch fisheries in Mexican North Pacific, where it is used for both food and bait. In this region, R. steindachneri is most frequently observed during summer months and is rare during winter. The large size at maturity, low fecundity, and schooling behavior of R. steindachneri indicate that this species could be particularly susceptible to overexploitation. A docile species that does well in captivity, this species and its congeners are often found in aquarium touch tanks and similar exhibits.
By Joseph J. Bizzarro
Pacific Shark Research Center
Moss Landing Marine Laboratories
8272 Moss Landing Road
Moss Landing, CA 95039
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