Author Archives: jkemper

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Featured Elasmobranch – Spotted Eagle Ray

November 2010

Photo Credit: Keith Wilson (2008)

Spotted Eagle Ray

Aetobatus narinari (Euphrasen, 1790)

Family Myliobatidae (Eagle Rays)

Identification: A distinct eagle ray with numerous white spots or rings on a black to bluish disc (occasionally greenish or pinkish), and white ventrally.  The disc is short and broad with highly angular pectoral fins.  The head is thick, with a distinctive fleshy, long, and rounded rostrum that is shaped like a duck-bill. Each jaw has a single row of flattened, bony plates designed for crushing prey, and the lower set is chevron-shaped.  The skin is uniformly smooth, without thorns or denticles.  The tail is extremely long and whip-like, reaching 2.5-3 times the length of the disc width, if undamaged.  The relatively short stinging spines (2-6 in number) are located near the base of the tail, just posterior to the small dorsal fin.

Size: Maximum total length for this species is 8.8 m (28.9 ft) with an undamaged tail.  The disc width has been reported to reach 3.3 m (10.8 ft), but typically is around 1.8 m (5.9 ft).  Size at birth varies from 17-36 cm  disc width (6.7-13.8 inches).  Males become sexually mature around 100 cm (3.3 ft) and females at 214 cm (7.0 ft) disc width.  Sexual maturity is reached by 4-6 years of age.  The maximum published weight is 230.0 kg (507.1 lbs).

Distribution: This species is the most common and widely distributed of the eagle rays.  It occurs worldwide in tropical and warm temperature seas.

Habitat: This circumtropical species can generally be found inshore in shallow water, often near reefs fringing continents, islands, and atolls, and even occasionally entering estuaries.  It has also been found to occur well offshore. Depth ranges from the intertidal zone to about 61 m (200 ft).  It is an active swimmer and can be seen near the surface singly, in pairs, or in large schools of up to 200, often leaping out of the water, or swimming near the bottom.

Biology:  Reproduction is ovoviviparous (also known as yolk-sac vivparity), meaning that the eggs develop and hatch within the mother with no additional maternal contribution beyond the yolk.  Copulation is brief, lasting from 30-90 second and takes place belly to belly.  Over the course of an hour, a single female may mate with up to four different males.  Females can give birth to 1-4 live young following a gestation period of about 12 months.  These rays use their flattened snouts to probe the sand and dig up hard-shelled molluscs including oysters, clams, and snails.  However, it is not rare for octopus, shrimp, urchins, worms, and bony fishes (which are targeted mainly by adults) to be consumed.

General interest:  The spotted eagle ray is of minor commercial importance, and is caught by trawls, trammelnets, and longlines.  The flesh is edible and consumed in some parts of the world, or used for fishmeal and fish oil. They are occasionally caught by hook-and-line and can only be landed after a great struggle.  Sharks often follow females during the birthing season to feed on newborn pups.  Atlantic, Indian and Pacific populations differ in color pattern and are likely to be separate species.  A spotless form, known as Aetobatus flagellum, is usually considered to be synonymous with this species.  The World Conservation Union (IUCN) Red List has assessed this species to be “Near Threatened” with populations declining worldwide.

By Jahnava Duryea
Graduate Student in Ichthyology
Moss Landing Marine Laboratories
8272 Moss Landing Road
Moss Landing, CA 95039