Aetobatus narinari

Geographic Range

Aetobatus narinari (spotted eagle ray) is globally distributed throughout tropical and warm temperate waters as far north as North Carolina, U.S.A. in the summer and as far south as Brazil. This species has also been known to inhabit the red sea and oceanic waters surrounding the Hawaiian islands. Its latitudinal range spans from 43°N to 32°S.

• Biogeographic Regions
• indian ocean
• atlantic ocean atlantic ocean
• pacific ocean pacific ocean

• Other Geographic Terms
• cosmopolitan cosmopolitan

Habitat

Aetobatus narinari is a reef associated ray and is commonly found along reef edges. It prefers warm water with soft bottoms consisting usually of mud, sand and gravel. Aetobatus narinari spends most of its time around 60 m deep but may dive up 80 m deep. It is often seen in beach areas as well as estuaries and mangrove swamps throughout tropical regions of the world.

• Habitat Regions
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic
• reef reef
• coastal coastal
• brackish water brackish water

• Other Habitat Features
• estuarine estuarine

Physical Description

Many eagle rays (including Aetobatus narinari ) have a flattened snout that protrudes from the pectoral disc. Aetobatus narinari can be distinguished by a pectoral disc that is approximately twice as wide as it is long. The posterior edge of the pectoral fins are concave and very angular tips (Bester, 2008). The ventral surface is white and the dorsal surface is either blue or black and peppered with white spots and rings. It has rounded pelvic fins and a very small dorsal fin but lacks a caudal fin all together. The pectoral fins make up a majority of the pectoral disc and are acutely angled at the lateral tips. Aetobatus narinari possesses stinging spines, which can be found behind the dorsal fin, and a slender whip-like tail that can be up to three times as long as the width of the pectoral disc (Bester, 2008). It can weigh as much as 230 kg and can reach disc widths of up to 330 cm; however, the average disc width of A. narinari is 180 cm. Sexual dimorphism has not been reported in this species.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry
• venomous venomous

Development

Aetobatus narinari is ovoviviparous, as its eggs develop inside the uterus and hatch within the mother prior to emerging. Once the embryos are released from the egg, they are nourished by a yolk sac rather than through a placental connection with the mother. Little is known of the development of A. narinari . Newborn pups generally measure 17 to 35 cm in disc width.

Reproduction

Prior to mating, multiple Aetobatus narinari males chase a single females while grasping her dorsum with their upper tooth plate. A single male then grabs one of the female's pectoral fins and roles her into a vertical position and inserts his claspers. Copulation can last from 20 to 90 seconds and females have been known to repeat this process up to 4 times over a relatively short period of time. The mating system of Aetobatus narinari has not been clearly defined; however, the competitive behavior of males prior to copulations suggests polygyny.

Breeding season in Aetobatus narinari varies by location but usually occurs during mid-summer. Typically, females give birth to 2 pups per pregnancy but can have between 1 and 4. Gestation lasts for approximately 12 months, but can be short as 8 months depending on location and mean water temperature during gestation. Evidence suggests that A. narinari becomes sexually mature when they grow to about half their maximum disc width, which typically occurs between 4 and 6 years of age.

• Key Reproductive Features
• seasonal breeding seasonal breeding
• sexual sexual
• fertilization fertilization
  • internal internal
• ovoviviparous ovoviviparous

Other than the in-utero protection and yolk sac a mother provides her young prior to birth, there is no information available regarding parental care in Aetobatus narinari .

• Parental Investment
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

There is no information available regarding the average life span of Aetobatus narinari .

Behavior

Aetobatus narinari feeds according to tide. During high tide, it typically forages for food and socializes with conspecific near sand flats. Mating usually occurs during high tide as well. When tide begins to fall, foraging activities taper off and it descends the water column to deeper water. At low tide, Aetobatus narinari often rests in large groups in deep water. The cycle repeats as tide rises. Aetobatus narinari is known to jump high out of the water, a behavior known as breaching. It is hypothesized that A. narinari breaches as an evasive maneuvering to avoid predation and as a method to remove ventrally attached parasites. Females have been observed giving birth during breaching, as the force of landing back in the water is thought to help push the pups out of the uterus. Aetobatus narinari has been documented traveling in schools ranging from 3 to 50 individuals. Schooling is thought to occur more often during breeding season and has been suggested as a predatory defense mechanism.

• Key Behaviors
• natatorial natatorial
• motile motile

Home Range

There is no information available regarding the average home range size of Aetobatus narinari .

Communication and Perception

As with all cartilaginous fishes , Aetobatus narinari has specialized electrosensory organs commonly referred to as Ampullae of Lorenzini. These sensory organs consists of jelly-filled pores that create an electrosensory network along the snout, which increases the sensitivity of A. narinari to prey movement, as muscle contractions create an electrical pulse. In general, elasmobranchs have excellent vision and olfactory perception, which help them avoid predators and detect prey. In addition, all fish have a lateral line system that allows them to sense changes in pressure and temperature in the surrounding environment. There is no information available regarding intraspecific communication in Aetobatus narinari .

• Perception Channels
• visual visual
• chemical chemical
• electric electric

Food Habits

Primary prey of Aetobatus narinari consists of crustaceans , molluscs , echinoderms and polychaete worms . It is also known to occasionally consume smaller fish as well. When a prey item is captured, A. narinari crushes it between the upper and lower dental plates. Prior to ingestion, it uses 6 to 7 rows of papillae located on the roof of the mouth to remove indigestible items (e.g., shell and bone).

• Primary Diet
• carnivore carnivore
  • eats non-insect arthropods
  • molluscivore molluscivore
  • vermivore

• Animal Foods
• fish
• mollusks
• aquatic or marine worms
• aquatic crustaceans
• echinoderms

Predation

Silvertip sharks and great hammerheads , are important predators of spotted eagle rays. Sharks have also been reported to follow spotted eagle rays during the birthing season in order to feed on newborn pups. Similar to other cartilaginous fishes , spotted eagle rays have a network of electrosensory organs on their snout that helps them detect potential predators. In addition, all fish have a lateral line system that allows them to detect changes in temperature and pressure in their immediate environment.

Ecosystem Roles

Spotted eagle rays are predators of a variety of marine invertebrates and are important prey for a number of shark species. Information regarding parasites specific to this species is limited, however, ectoparasites such as marine leeches, are thought to be common. Endoparasites such as trematodes and tapeworms, are common as well.

Economic Importance for Humans: Positive

Although spotted eagle rays are sometimes targeted for their meat, detailed accounts of captures are limited.

• Positive Impacts
• food food

Economic Importance for Humans: Negative

Spotted eagle rays are capable of stinging humans with their venomous spine, which occasionally results in death. There are a few documented cases of spotted eagle rays jumping out of the water and onto boats.

• Negative Impacts
• injures humans
  • bites or stings
  • venomous venomous

Conservation Status

Aetobatus narinari is listed as near threatened on the IUCN's Red List of Theatened Species. Although detailed accounts of its capture are limited, small litter sizes, schooling tendencies and inshore habitat preferences make this species particularly vulnerable to overfishing. In addition, in shore fishing gear (beach seine, gillnet, trawl etc.) is widely available and the practice of in shore fishing is largely unregulated, resulting in the IUCN's near threatened listing. In shore fishing pressure on A. narinari is particularly intense in southeast Asia. As a result, the IUCN classifies this species as vulnerable in this part of its geographic range.

Aetobatus narinari is protected in Australia, the Maldives, and Florida. Much of its geographic range in Australia's coastal waters includes the Great Barrier Reef, a third of which is protected against fishing. In addition, the use of turtle exclusion devices is mandatory in prawn trawl fisheries of Northern Australia, which likely decreases by-catch. The export of rays and ray skins was banned in the Maldives in 1995 and 1996, respectively. In addition, elasmobranchs are protected in marine reserves surrounding the Maldives that attract ecotourists interested in marine wildlife. Finally, A. narinari cannot be harvested, possessed, landed, purchased, sold or exchanged in Florida.

Additional Links

Encyclopedia of Life

Contributors

tom pederson (author), Augsburg College, Kevin Potts (editor), Augsburg College, John Berini (editor), Animal Diversity Web Staff.

References

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Breder, C., D. Rosen. 1966. Modes of reproduction in fishes . Neptune City, New Jersey: T.F.H. Publications.

Breder, C., D. Rosen. 1966. "Modes of reproduction in fishes" (On-line). T.F.H. Publications. Accessed April 22, 2011 at http://www.fishbase.org/references/FBRefSummary.php?id=205&speccode=1256 .

Compagno, L., D. Ebert, M. Smale, London. 1989.

Guide to the sharks and rays of southern Africa

Florida Museum of Natural History, 2005. "2005 Biological profiles: spotted eagle ray" (On-line). Accessed April 21, 2011 at www.flmnh.ufl.edu/fish/Gallery/Descript/SERay/SERay.htmlhttp://www.flmnh.ufl.edu/fish/Gallery/Descript/SERay/SERay.html .

Humann, P. 1989. Reef Fish Identification . Jacksonville, Florida: New World Publications Inc..

Kyne, P., H. Ishihara, S. Dudley, W. White. 2006. "Aetobatus narinari" (On-line). IUCN Red List of Threatened Species. Accessed April 24, 2011 at http://www.iucnredlist.org/apps/redlist/details/39415/0 .

Ochumba , . 1988. The distribution of skates and rays along the Kenyan coast. Journal of East African History and Nature , 78: 192.

Robins, C., R. G.C.. 1986. A field guide to Atlantic coast fishes of North America . Boston, U.S.A.: Houghton Mifflin Company.

2005. "Coral Reef Creatures" (On-line). Beatiful Oceans. Accessed May 01, 2011 at http://www.beautifuloceans.com/creatures/n-to-z/spotted-eagle-ray/224-spotted-eagle-ray-aetobatus-narinari.html .