Spotted eagle ray

Spotted eagle ray Temporal range: Upper Cretaceous–Recent[1] PreЄ Є O S D C P T J K Pg N
Conservation status
Near Threatened (IUCN 3.1)[2]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Order:	Myliobatiformes
Family:	Myliobatidae
Genus:	Aetobatus
Species:	A. narinari
Binomial name
Aetobatus narinari (Euphrasén, 1790)[3]
Range of spotted eagle rays
Synonyms[4]
Aetobatis latirostris Aetobatis narinari Aetomylus maculatus Myliobatis eeltenkee Myliobatis macroptera Myliobatus punctatus Raia quinqueaculeata Raja narinari Stoasodon narinari

The spotted eagle ray (Aetobatus narinari) is a cartilaginous fish of the eagle ray family. It can be found globally in tropical regions, including the Gulf of Mexico, Hawaii, off the coast of West Africa, the Indian Ocean, Oceania, and on both coasts of the Americas at depths down to about 80 meters (262 ft). Rays are ovoviviparous, the female retaining the eggs, then releasing the young as miniature versions of the parent. The ray can be identified by its dark ventral surface covered in white spots or rings. Near the base of the ray's relatively long tail, just behind the pelvic fins, are several venomous, barbed stingers. Spotted eagle rays commonly feed on small fish and crustaceans, and will sometimes dig with their snouts to look for food buried in the sand of the sea bed. These rays are commonly spotted leaping out of the water, and on at least two occasions have been reported as having jumped into boats, in one incident resulting in the death of a woman in the Florida Keys.

Taxonomy

The spotted eagle ray was first described by Swedish botanist Bengt Anders Euphrasén as Raja narinari in 1790 while he was on a naturalist trip to the Antilles, and later as Stoasodon narinari.^[3][4][5] Its current genus name is Ateobatus, derived from the Greek words aetos (eagle) and batis (ray). The spotted eagle ray belongs to the Myliobatidae family, which includes the commonly known Manta ray. Most rays in the Myliobatidae swim in the open ocean rather than close to the sea floor.^[4] The spotted eagle ray has many different common names, including white-spotted eagle ray, bonnet skate, bonnet ray, duckbill ray and spotted duck-billed ray.^[6][7][8]

Description and behavior

Close up of the head

Spotted eagle rays have flat disk-shaped bodies, deep blue or black with white spots on top with a white underbelly, and distinctive flat snouts similar to a duck's bill.^[9] Their tails are longer than those of other rays, and may have 2–6 venomous spines.^[4] The front half of the long and wing-like pectoral disk has five small gills in its underside; the rays' barbed stingers are just behind the pelvic fins.^[10]

Mature spotted eagle rays can be up to 5 meters (16 ft) in length; the largest have a wingspan of up to 3 meters (10 ft) and a mass of 230 kilograms (507 lb).^[11][12]

Reproduction

One male, or sometimes several, will pursue a female. When one of the males approaches the female, he uses his upper tooth plate to grab her dorsum. The male will then roll the female over by grabbing one of her pectoral fins, which are located on either side of her body. Once she is on her ventral side, the male puts a clasper into the female, connecting them venter to venter, with both undersides together. The mating process can last anywhere from thirty to ninety seconds.^[4]

The spotted eagle ray develops ovoviviparously, that is, the eggs are retained in the female and hatch internally first, feeding off a yolk sac until live birth.^[4] The gestation period for these rays is one year. At the end of this period, the mother ray will give birth to a maximum of four pups.^[2] When the pups are first born, their discs measure from 170–350 millimeters (6.7–14 in) across.^[4] The rays mature in 4 to 6 years.^[2]

Feeding and diet

Spotted eagle ray preys mainly upon bivalves, shrimps, crabs, whelks, and other benthic infauna. The spotted eagle ray's specialized chevron-shaped tooth structure helps it to crush the mollusks' hard shells.^[11][12] They feed on mollusks and crustaceans, particularly malacostracans.^[13][14] and also upon hermit crabs,^[15] shrimp, octopi, and some small fish.^[16] These rays have several distinctive behaviors, including digging with their snouts in the sand of the ocean. ^[17] While doing this, a cloud of sand surrounds the ray and sand spews from its gills. One study has shown that there are no differences in the feeding habits of males and females or in rays from different regions.^[14] The jaws of these rays have developed calcified struts to help them break through the shells of mollusks, by supporting the jaws and preventing dents from hard prey.^[1]

Behavior

Underside of the body

Spotted eagle rays prefer to swim in waters of 24 to 27 °C (75 to 81 °F). Their daily movement is influenced by the tides; one tracking study showed that they are more active during high tides. These rays have several distinctive behaviors including digging with their snouts in the sand,^[17] during which a cloud of sand surrounds the ray and sand spews from its gills. The spotted eagle ray also exhibits two motions in which the abdomen and the pectoral fins are moved rapidly up and down: the pelvic thrust and the extreme pelvic thrust. The pelvic thrust is usually one ray alone and repeated four to five times rapidly. The extreme pelvic thrust is most commonly observed when the ray is swimming in a group, from which it will separate itself before vigorously thrusting with its pectoral fins. The rays also performs dips and jumps; in a dip the ray will dive and then come back up rapidly, perhaps as many as five times consecutively. There are two main types of jump: in one, the ray propels itself vertically out of the water, to which it returns along the same line; the other is when the ray leaps at a 45 degree angle, often repeated multiple times at high speeds. When in shallow waters or outside their normal swimming areas the rays are most commonly seen alone, but they do also congregate in schools. One form of traveling is called loose aggregation, which is when three to sixteen rays are swimming in a loose group, with occasional interactions between them. A school commonly consists of six or more rays swimming in the same direction at exactly the same speed.^[18]

Human interaction

In the public aquarium uShaka Marine World, South Africa

The dorsal spots make the spotted eagle ray an aquarium attraction, although because of its large size it is likely kept only at public aquariums.^[6] There are no target fisheries for the spotted eagle ray, but it is often eaten after being caught unintentionally as bycatch.^[6] Although interaction with humans is rare, there have been cases of humans encountering these animals. In March 2008 a woman was sunbathing on her boat in the Florida Keys when a 34-kilogram (75 lb) spotted eagle ray struck her on the head, resulting in her death.^[19] A few years later another woman was struck by an eagle ray in the same area as she was taking pictures of rays jumping in front of her. It leaped into her boat and hit her in the chest, knocking her over, and then thrashed around on top of her. The ray was 2.4 meters (8 ft) wide with a 3-meter (10 ft) tail and weighed about 135 kilograms (300 lb). After a few moments the woman succeeded in freeing herself, unharmed.^[20] Nevertheless spotted eagle rays do not pose a significant threat to humans, as they are shy and generally avoid human contact.^[4]

Predators

The silvertip shark is a predator of the spotted eagle ray.

Spotted eagle rays, in common with many other rays, often fall victim to sharks such as the tiger shark, the lemon shark, the bull shark, the silver tip shark, and the great hammerhead shark.^[21][22] A great hammerhead shark has been observed attacking a spotted eagle ray in open water by taking a large bite out of one of its pectoral fins, thus incapacitating the ray. The shark then used its head to pin the ray to the bottom and pivoted to take the ray in its jaws, head first.^[23] Sharks have also been observed to follow female rays during the birthing season, and feed on the newborn pups.^[4]

Habitat and distribution

An eagle ray searching the bottom for food

Spotted eagle rays are found globally in tropical regions, including the Gulf of Mexico, Hawaii, Atlantic Africa, the Indian Ocean, Oceania, and the Pacific west coast.^[4][11]

They are found in shallow coastal water by coral reefs and bays, in depths down to 80 meters (262 ft).^[11] Spotted eagle rays are found in warm, temperate, waters worldwide. In the waters of the West-Atlantic Ocean, off the coast of North Carolina and Florida, in the Gulf Stream, in the Caribbean, and down past the southern part of Brazil. In the West-Pacific Ocean, it can be found from the Red Sea to South Africa and also in northern Japan and Australia.^[4] The ray can also be found in the Eastern-Pacific Ocean from the Gulf of California down through Puerto Pizarro, an area that includes the Galapagos Islands. Spotted eagle rays are most commonly seen in bays and reef areas. They spend much of their time swimming freely in open waters. Generally swimming in schools close to the surface, they can travel long distances in a day.^[4]

Conservation

The spotted eagle ray is included in the IUCN's Red List as "near threatened". The rays are caught mainly in Southeast Asia and Africa. They are also common in commercial marine life trade and are displayed in aquariums. Among the many efforts to help protect this species, South Africa's decision to deploy fewer protective shark nets has reduced the number of deaths caused by entanglement. South Africa has also placed restrictions on the number of rays that can be bought per person per day. In the state of Florida in the United States, the fishing, landing, purchasing and trading of spotted eagle ray is outlawed. The spotted eagle ray is also protected in the Great Barrier Reef on the eastern coast of Australia.^[3]

References

1. ^ ^{a b} Summers, Adam (2001). "Aetobatus narinari". Digital Morphology. http://digimorph.org/specimens/Aetobatus_narinari/upperjaw/. Retrieved 1 November 2011. 
2. ^ ^{a b c} Kyne, P.M., Ishihara, H., Dudley, S. F. J. & White, W. T. (2006). Aetobatus narinari. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 24 February 2009.
3. ^ ^{a b c} Kyne, Ishihara. "Aetobatus narinari". IUCN 2011. http://www.iucnredlist.org/apps/redlist/details/39415/0. Retrieved 23 October 2011. 
4. ^ ^{a b c d e f g h i j k l} Bester, Cathleen. "Ichtyology at the Florida Museum of Natural History". Florida Museum of Natural History. http://www.flmnh.ufl.edu/fish/gallery/descript/seray/seray.html. Retrieved 21 October 2011. 
5. ^ (in German) Symbolae Antillanae : seu fundamenta florae Indiae Occidenttalis. Berolini : Fratres Borntraeger ; Parisiis : Paul Klincksieck. http://www.archive.org/details/symbolaeantillanv3pt1urba. Retrieved 2011-10-27. 
6. ^ ^{a b c} Fowler, Sarah L; Cavanagh, Rachael D (2005). "Species status report". Sharks, rays, chimaeras: The status of the Chondrichthyan fishes. UK: IUCN. p. 354. ISBN 2831707005. http://books.google.com/books?id=z6scNrsln2MC&pg=PA354. 
7. ^ Daley, R K; Stevens, J D; Last, P R; Yearsley, G. K. (October 2002). "Northern demersal species". Field guide to Australian sharks and rays. Australia: CSIRO Marine Research. p. 44. ISBN 1876996102. http://books.google.com/books?id=9yIPeavWykwC&pg=PA44. 
8. ^ Tee-Van 1953, p. 453
9. ^ "White-Spotted Eagle Ray". http://www.ozanimals.com/Fish/White-spotted-Eagle-Ray/Aetobatus/narinari.html. Retrieved 29 October 2011. 
10. ^ Carpenter, Kent E.; Niem, Volker H.. "The Living Marine Resources of the Western Central Pacific". pp. 1511, 1516. ftp://ftp.fao.org/docrep/fao/009/x2401e/x2401e12.pdf. Retrieved 30  October 2011. 
11. ^ ^{a b c d} Luna, Susan M. "Aetobatus narinari – Species Summary". Fish Base. 30 April 2007. WorldFish Center. 3 June 2007.
12. ^ ^{a b} "Spotted Eagle Ray". Elasmodiver. 3 June 2007.
13. ^ "Eagle Ray Spotted Eagle Ray Aetobatus narinari". http://www.cayman.org/fauna/eagle.htm. Retrieved 18 October 2011. 
14. ^ ^{a b} "Life History, Population Genetics and Sensory Biology of the White Spotted Eagle Ray Aetobatus narinari (Euphrasen, 1790) with Emphasis on the Relative Importance of Olfaction". http://espace.library.uq.edu.au/view/UQ:151742. Retrieved 18 October 2011. 
15. ^ Schluessel, V; Bennett, M. B.; Collin, S. P.. "Diet and reproduction in the white-spotted eagle ray Aetobatus narinari from Queensland, Australia and the Penghu Islands, Taiwan". http://espace.library.uq.edu.au/view/UQ:223468. Retrieved 1 November 2011. 
16. ^ SeaWorld. "Spotted Eagle Ray". http://www.seaworld.org/animal-info/animal-bytes/animalia/eumetazoa/coelomates/deuterostomes/chordata/craniata/chondrichthyes/batoidea/myliobatiformes/spotted-eagle-ray.htm. Retrieved 1 November 2011. 
17. ^ ^{a b} Silliman 1999, p. 5.
18. ^ Silliman 1999, pp. 5–6.
19. ^ CNN. "Woman dies after stingray strikes her". Cable News Network. A Time Warner Company. http://edition.cnn.com/2008/US/03/20/stingray/. Retrieved 30 October 2011. 
20. ^ CNN. "Ray slams woman on boat in Florida Keys". Cable News Network. A Time Warner Company. http://articles.cnn.com/2011-03-29/us/florida.ray.tourist_1_tour-boat-ray-barbed-tails?_s=PM:US. Retrieved 30 October 2011. 
21. ^ Silliman 1999, p. 2.
22. ^ "Spotted Eagle Ray, Aetobatus narinari". marinebio.org. http://marinebio.org/species.asp?id=58. Retrieved 9 November 2011. 
23. ^ Chapman 2002, p. 949.

Bibliography

• Carpenter, Kent E.; Niem, Volker H. (1999). "Batoid fishes". The Living Marine Resources of the Western Central Pacific. Batoid fishes, chimaeras and bony fishes. 3. pp. 1511, 1516. ISBN 92-5-104302-7. ftp://ftp.fao.org/docrep/fao/009/x2401e/x2401e12.pdf. 
• Chapman, D.D.; Gruber, S.H. (May 2002). "A further observation of the prey-handling behavior of the great hammerhead shark, Sphyrna mokarran: predation upon the spotted eagle ray, Aetobatus narinari". Bulletin of Marine Science 70 (3): 947–952. http://www6.miami.edu/sharklab/images/Papers/Chapman%20and%20Gruber_2002.pdf. Retrieved 31 October 2011. 
• Silliman, William R.; Gruber, S.H. (1999). "Behavioral Biology of the Spotted Eagle Ray, Aetobatus narinari (Euphrasen, 1790), in Bimini, Bahamas; an Interim Report" (pdf). http://www6.miami.edu/sharklab/images/Papers/Silliman%20and%20Gruber_1999.pdf. Retrieved 31 October 2011. 
• Tee-Van, John (1953). "Family Myliobatidae, Genus Aetobatus". Fishes of the western North Atlantic, part two. New Haven,Sears Foundation for Marine Research, Yale Univ.. pp. 253–263. http://www.archive.org/details/fishesofwesternn02teev. Retrieved 2011-10-27. 

External links

• Information and pictures of the spotted eagle ray
• White-spotted Eagle Ray, Aetobatus narinari (Euphrasén, 1790) – Australian Museum