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What People Say

The program is designed for any person with an interest in coral reef biology. All the information was presented in a clear step by step manner making it thus easy to understand - nice pictures as well! You really prepare the "entry-level" diver or snorkeler for what he will be observing as he passes through the different zones of the reef. I had alot of fun!

Jose, High school student, snorkeler, 18 years, Montreal


     
Spotted Eagle Ray - Aetobatus narinari PDF Print E-mail

 

spotted_eagle_ray_aetobatus_narinari

Who?

Family: Myliobatidae
Species: Aetobatus narinari
Species ID: M.AN

Description: A diamond-shaped ray with large triangular pectoral fins (1) and a large head and snout (2). The eyes and spiracles (which pump water to the gills) are located on the sides of the head. Two small pelvic fins flank the long, whip-like tail (3) which bears stinging spines. The back is grey to dark brown and covered in small white spots or rings (4), while the belly is pale. Males are distinguished by their external sex organs – small, fingerlike projections called ‘claspers’ found on the ends of the pelvic fins. Juveniles resemble adults

Maximum Size: 2.3 m (7.5 ft) disk diameter
Longevity: Unknown, but likely up to 19 years based on the longevity of other eagle rays.
Status: Near threatened according to the IUCN endangered species list
Spotted Eagle Rays & People: This species is eaten locally, but not commercially important. They are considered a pest in mariculture, and are sometimes killed to prevent them from feeding on farmed shellfish


Where?

Geographical Range: Found throughout the world’s tropical oceans
Coral Reef Zone: Found in the back reef, fore reef and drop-off zones, and also the open ocean
Favourite Habitat: Spotted eagle rays feed over sandy bottoms, but often move to offshore surface waters to rest, socialize, and reproduce
Depth: 1–80 m ( 3–260 ft)

A Day in The Life:

The spotted eagle ray does not follow the regular day/night cycle of most creatures, but instead follows a routine set by the tides.

High tide: Eagle rays forage for food and socialize on sand flats; mating may also occur
Falling tide: Foraging activity tails off and eagle rays begin to move offshore
Low tide: Eagle rays rest offshore, often in groups
Rising tide: Eagle rays begin to move inshore towards feeding areas


Who Eats Who?

The spotted eagle ray is a carnivore that specializes in eating hard-shelled prey such as snails, clams, crabs, and lobster, as well as octopuses and occasionally fishes. Eagle rays are large and potentially dangerous prey, and are fed on by only the largest coral reef predators, such as tiger, bull, lemon, and hammerhead sharks.

Scuba Diver & Snorkeler Best Practices

Participate in environmental initiatives. Participate in underwater cleanup projects and public education efforts whenever possible. These initiatives make a huge difference to the coral reef, and help spread word of eco-diving best practices.


What?

Approach

Spotted eagle rays are shy and tend to avoid divers and snorkellers. Staying still and breathing slowly can encourage rays to approach more closely. Eagle rays that are busy feeding are more easily approached.

Feeding Behaviour
Spotted eagle rays are carnivores that specialize in feeding on hard-shelled prey such as shellfish. They are often seen feeding during the day, though they may also feed at night (see previous note about tidal cycle). Eagle rays feed primarily over sand flats and occasionally in rocky areas. They have electroreceptors in their snout that enable them to detect the weak electric signals generated by the muscles of prey buried in the sand. Once they detect their prey, they excavate the area with their snout, raising large clouds of sand in the process. These rays have also been known to poke their heads into caves and crevices and even overturn rocks in their search for food. Once captured, the hard shells of their prey are crushed between two bony plates in the jaw; hard parts are spat out, while soft parts are swallowed.

Observe, record & share:

O M.AN-101 – Scanning: Eagle rays move over the bottom using electroreceptors in their snout to detect prey buried in the sand
O M.AN-102 – Digging: Rays dig their prey from the sand using their scoop-like snout
O M.AN-103 – Moving objects: Rays stick their head into caves and crevices and may even move rocks in their search for food

Attack & Defense Behaviour
Spotted eagle rays are generally docile, have few predators, and rely mainly on their speed and agility to avoid predation. If a perceived threat moves too close, these rays will attempt to escape, and may make sharp turns and other evasive maneuvers to avoid being caught. In some cases, eagle rays have been known to leap out of the water when chased. If cornered or caught, the eagle ray may attempt to sting using its tail. Spotted eagle rays sometimes form large schools which are thought to have defensive benefits, but may also help them in finding a mate.

Observe, record & share:

O M.AN-201 – Escape: Rays accelerate away from threats and make sharp, evasive turns
O M.AN-202 – Schooling: Spotted eagle rays can form schools consisting of up to 50 individuals
O M.AN-203 – Leaping: Rays sometimes leap out of the water to escape predators
O M.AN-204 – Stinging: Rays may thrash their tail in order to sting a predator with their spines

Reproductive Behaviour
Spotted eagle rays, like sharks, reproduce sexually by internal fertilization and give birth to up to four pups per litter after a long gestation period of roughly one year. During the breeding season, male spotted eagle rays closely follow females, nibbling or biting their back in an act of courtship. Males bite and hold the edge of the female’s pectoral fins for support. The male then flips his body under the female in order to mate, after which the male either swims away or remains near in order to mate again. Unreceptive females rise to the surface and slap their fins against the water to drive males away. Pregnant females give birth in open water, and some females have even been recorded leaping from the water while giving birth. It is believed that they do so because the impact of entering the water may help push out the pups. Unfortunately, little is known about the seasonal timing of reproduction in this species.

Observe, record & share:

O M.AN-301 – Following: One or more males closely follow a female
O M.AN-302 – Back biting: Males nuzzle and bite the back of females they court
O M.AN-303 – Fin biting: A male will grip the trailing edge of the female’s pectoral fin
O M.AN-304 – Mating: The anchored male flips beneath the female and mating occurs
O M.AN-305 – Unreceptive female: Females uninterested in mating rise to the surface and slap their fins against the water to drive males away
OM.AN-306 – Birth: Females give birth to live young, sometimes leaping from the water to help with labour


Highlight Behaviour

Courtship: Spotted eagle rays show courtship behaviours that are typical of many other rays and even sharks. Courtship begins when males follow females closely (1) and begin biting their back and fins (2), a courtship ritual that is very common among rays and sharks. Although this may seem painful, studies have shown that females are protected from these “love bites” by their exceptionally thick skin, which is typically three to four times thicker than that of males. Once a male spotted eagle ray has a tight grip on the female (3), he swivels his body beneath hers (4) and inserts his reproductive organ, known as a clasper. Mating continues for roughly a minute before the couple parts ways.

Did You Know?

• The spotted eagle ray has one of the highest brain to body mass ratios among fish, a criteria usually used to estimate relative intelligence. This means eagle rays are likely to be one of the smarter marine creatures. In support of this finding, spotted eagle rays are known to have complex social systems and behaviours, many of which are still not fully understood.
• Despite all the hard-shelled prey they eat, pieces of shell are almost never found in the stomachs of spotted eagle rays. Six or seven papillae – projections that resemble small tongues – are located behind each of the crushing mouth plates. The papillae selectively pick out pieces of shell and move them forward so they can be expelled rather than swallowed.

What to do?

Share your observations today! Discover your species of interest, observe its behaviour, and share your pictures and videos with friends and coral reef enthusiasts around the world! Upload media to the web, tagged with species common name (ex.: trumpetfish) and species ID code (ex.: A.AM) or species behaviour code (ex.: A.AM-101)

Observation Key

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