Any diver who has witnessed a flight of eagle rays gliding along a coral wall will understand why these polka dot-clad fish – yes rays are fish – are likened to birds of prey. The graceful motions of their wing-like pectoral fins give eagle rays the appearance of soaring rather than swimming.
Of the 19 members of the eagle ray family, it is the spotted eagle ray that divers are most likely to encounter. They live in tropical and semi-tropical waters around the world, from the coast of Africa to the Caribbean, the tropical Pacific and the Indian Ocean. The largest spotted eagle rays may tip the scales at 300 pounds and display seven-foot wingspans. But really big specimens are rare, and divers are far more likely to run into rays that are half that size.
The eagle ray's distinctive color pattern is a strategic adaptation that helps it blend into the environment and hide from sharks, which are the ray's only predator. The spotted topside breaks up the ray's profile when seen from above, making it more difficult for a shark to single it out against a mottled seabed. In similar fashion, the light-colored underside blends into the lighter shades of the surface water when viewed from below.
These rays do not seek out human interactions the way their manta ray cousins will sometimes do and instead tend to ignore or shy away from divers. They are non-aggressive but are equipped with poisonous barbs at the base of their long tails. These stingers are not used to subdue prey and are deployed only when the ray is threatened.
Unlike their namesake bird, which relies on keen eyesight to identify prey, the eagle ray uses other senses to find food. The ray's pronounced bulbous beak is packed with electro-sensitive pores that allow them to detect crustaceans hidden in the sand – a sort of biological radar. When the ray detects dinner, the nose is used to dig into the sand to unearth a meal. Their diet includes clams, snails, crabs, worms and shrimp, and they are equipped with special teeth that can crush hard-shelled prey.
If you come across an eagle ray rooting through the sand in search of a meal, you may notice that it is followed by one or more small fish. These fish are shadow feeding, looking for small morsels unearthed by the ray's excavations. For divers who keep a respectable distance and don't spook the ray this behavior can be quite fascinating to watch. Marine biologists report that rays are more likely to be seen foraging in the sand during high tide.
Eagle rays are solitary much of the time, but they will sometimes be seen in loose aggregations on a reef or sand bed, and from time to time they will travel together in formation. Like mantas and other rays, they are susceptible to parasites and can sometimes be seen at reef cleaning stations having pesky parasites removed by small fish or shrimp.
Eagle rays will sometimes take to the air. These brief flights, which can reach heights of six feet, are thought to be done to shake free of remoras and other parasites. Marine biologists have also suggested that the males will leap to show off for the ladies. If this display of prowess is successful and there's a mutual attraction, the flirting pair may engage in an underwater ballet that can last for several hours as the suitors circle and glide in unison.
These romances are relativity rare, as eagle rays are not prolific breeders, reaching sexual maturity at between four and six years of age and taking anywhere from six to 12 months to produce a litter of one to five babies. Mothers are ovoviviparous, which means they hold their eggs inside until they hatch, with the developing youngsters drawing their nutrition from the egg yolk rather than the mother.
Eagle rays have a lifespan of around 25 years, and staying alive is largely about avoiding sharks. They are rarely targeted by fishermen but will sometimes show up as bycatch in trawls and gill nets. Like other coastal species, they are susceptible to habitat loss caused by development. As a result, these rays are often listed as threatened but not endangered.
An eagle ray sighting can be the highlight of a dive. If you are lucky enough to come across a ray rooting through a sand bed the spectacle can provide an entertaining interlude. Equally memorable is witnessing a flight of eagle rays soaring overhead in formation.