What Do Spotted Eagle Rays Eat?

Spotted eagle rays eat hard-shelled mollusks, primarily clams and other bivalves, along with snails and a smaller proportion of crustaceans. Their diet is remarkably specialized compared to many other ray species. A detailed gut-content study in Bermuda found that a single clam species, the calico clam, accounted for more than 86% of all individual prey items consumed, with some rays carrying over 150 clams in their stomachs at one time.¹ That said, the menu varies by region, individual size, and local prey availability, and the story of how these rays find and process their food is worth understanding in its own right.

What Shows Up in Their Stomachs

The most thorough look at spotted eagle ray diet comes from Bermuda, where researchers examined the gut contents of rays collected in Harrington Sound. The results were strikingly lopsided. Calico clams were by far the dominant prey, appearing in about 79% of rays examined and making up roughly 86% of all individual prey items by count. Five different rays, both male and female, had more than a hundred calico clams in their stomachs. One individual held 161 clams.¹

Other bivalves made smaller but consistent appearances in the diet. These included lucine clams, eared arks, and purplish tagelus, each showing up in a modest fraction of the stomachs examined. Gastropods, or snails, were rarer. Only one large female was found to have eaten gastropods, specifically moon snails and milk conch.¹ An interesting detail: 80% of the rays examined had only a single prey species in their gut, suggesting that when a spotted eagle ray finds a productive patch of clams, it tends to stay put and eat one thing rather than grazing on a mixture.

The total amount of food in a ray’s stomach at any given time ranged from less than 1% to about 8.5% of its body weight, averaging around 5%. Most of the ingested material was intact or nearly intact shells, with very few shell fragments, which tells researchers something important about how these animals process their food before swallowing.

Regional and Age-Related Differences in Diet

The Bermuda picture is not universal. In Queensland, Australia, and the Penghu Islands off Taiwan, researchers found a broader menu and a clear shift in diet as the rays grow. Small spotted eagle rays leaned heavily on gastropods and crustaceans, with gastropods making up about 53% and crustaceans about 43% of the diet by mass. Bivalves were barely on the radar for young rays, contributing only around 4% of food intake.²

As the rays grew, their diet composition changed. Medium-sized individuals ate a more mixed diet in which mollusks overall (gastropods plus bivalves) rose to about 71% by mass and crustaceans dropped to about 21%. In the largest size class, crustaceans shrank further to roughly 12% of the diet while bivalves surged to about 36%. Gastropods remained the single largest prey category even among the biggest rays, at around 52%.²

This pattern makes intuitive sense. Crushing thick bivalve shells requires considerable jaw strength, and younger rays with smaller jaws may simply not be able to crack them efficiently. Snails and small crustaceans like crabs and shrimp offer a softer or more accessible meal. As the ray grows and its crushing apparatus develops, harder-shelled bivalves become increasingly worthwhile.

Built to Crush Shells

The reason spotted eagle rays can handle such a specialized diet lies in their jaw anatomy. Like other shell-crushing, or “durophagous,” rays, they have rigid jaws lined with flat teeth that lock together into broad, pavement-like plates. These plates act as a grinding surface, and large jaw muscles generate enough bite force to fracture tough biological composites like mollusk shell.³ If you have ever struggled to crack open a clam with a kitchen tool, consider that an eagle ray does this hundreds of times in a single feeding bout using nothing but its mouth.

The teeth themselves are unlike the sharp, pointed teeth most people associate with sharks and rays. Instead of piercing or tearing, they form a flat mosaic designed purely for compression. The upper and lower tooth plates meet like a nutcracker, distributing force across the whole shell surface. This design allows the ray to crack the shell cleanly, extract the soft tissue inside, and swallow it with minimal shell fragmentation, which is consistent with the observation from gut studies that most ingested shells are largely intact.

How They Find Buried Prey

Clams and other bivalves spend most of their lives buried in sandy or muddy substrate, which means spotted eagle rays need a way to locate prey they cannot see. Their solution is a distinctively shaped snout. The front of an eagle ray’s head features two fused structures called cephalic lobes, which form a flat, delta-shaped rostrum that angles downward when the ray is foraging. This shape is not just cosmetic. Researchers studying the hydrodynamics of this structure found that when the lobes angle down near a solid surface, they generate negative lift, essentially pushing the ray’s sensory apparatus into the sediment.⁴

This matters because eagle rays are powerful swimmers, and the flapping of their large pectoral fins creates pitching motions that would otherwise bounce the snout away from the bottom. The negative lift generated by the cephalic lobes counteracts that upward pitch and keeps the ray’s electroreceptive and mechanosensory organs in firm contact with the substrate.⁴ The ray sweeps this shovel-like snout across the sand, detecting the electrical signals and vibrations of burrowed clams, then uses the same snout to excavate them before crushing and swallowing them.

If you watch a spotted eagle ray foraging, it looks like it is plowing a furrow across the seafloor. It leaves visible trails in the sediment, and these feeding pits can be substantial enough that researchers have used them to map foraging activity even without seeing the rays themselves.

When They Prefer to Feed

Spotted eagle rays do not feed uniformly throughout the day. Acoustic tracking data from Bermuda revealed a pronounced shift in how rays used the water column depending on time of day. During dark hours, from roughly midnight to 5 a.m. and again from 6 p.m. to midnight, the highest proportion of detections were near the surface, at about 0.7 meters deep, suggesting the rays were resting or cruising in subsurface waters during low-light conditions. During daylight hours, this pattern reversed dramatically. Late morning saw a more even spread across depths, and by afternoon the rays had moved significantly deeper, with peak use around 5.5 meters.⁵

This diel pattern has practical implications for understanding when eagle rays are likely to be feeding on benthic prey. Moving to deeper water during the day is consistent with bottom-foraging activity over shallow flats and seagrass beds, which are prime clam habitat. The timing also matters in contexts where eagle ray feeding overlaps with human interests, as we will see below.

The Conflict with Shellfish Farmers

Wherever spotted eagle rays share habitat with commercial clam operations, tension follows. In Florida’s Indian River Lagoon, researchers used acoustic telemetry to monitor how both whitespotted eagle rays and cownose rays interacted with shellfish aquaculture leases. They found that while visits to clam lease sites made up a modest portion of total detections (about 6% for eagle rays), the visits that did occur were sometimes very long. Both species had visits exceeding 17 minutes, and the longest recorded visit lasted nearly six and a half hours.⁶

A telling detail from that study: 84% of all visits were from whitespotted eagle rays rather than cownose rays, and the longest eagle ray visits happened at night. Since most clamming operations run during daytime morning hours, these nighttime foraging bouts are easy to miss. The researchers noted that observed interactions with clam leases are likely underestimated for this reason.⁶ A clam farmer who checks the beds each morning may not realize that a ray spent half the previous night there.

This conflict is not trivial. Shellfish aquaculture is a growing industry in coastal waters of the southeastern United States, and losses to ray predation can be financially significant for individual farmers. At the same time, spotted eagle rays are increasingly recognized as species of conservation concern, and lethal removal is not a sustainable or widely accepted management strategy. Solutions currently being explored include physical exclusion devices like nets and cages over lease sites, though these add cost and complexity to operations.

Sharing the Table with Cownose Rays

Spotted eagle rays and cownose rays look similar at first glance and eat many of the same things, which raises the question of whether they compete directly for food. Stable isotope analysis of both species along Australia’s east coast found substantial overlap in their trophic niches, ranging from about 57% to 75% depending on the modeling approach used.⁷ In other words, more than half of what these two species eat comes from the same general pool of prey types and habitats.

The cownose ray’s niche was smaller and more constrained, meaning it feeds from a narrower range of sources, while the eagle ray’s diet was somewhat broader.⁷ This overlap matters ecologically because both species can be abundant in the same coastal waters. Whether it leads to real competition depends on whether prey is scarce enough to limit either population, which is a question researchers are still working to answer. In areas with abundant shellfish beds, the overlap may be irrelevant; in depleted habitats or near aquaculture operations, it could amplify the combined impact on benthic prey communities.

What Eats the Eagle Ray

For all their size and armor-like skin, spotted eagle rays are themselves prey. Great hammerhead sharks are among their most significant predators, and they seem to have a particular taste for rays. Great hammerheads are unusual among large coastal sharks in that their diet is dominated by other sharks, rays, and large bony fishes, rather than the smaller fish, crustaceans, and mollusks that most big sharks eat. Researchers have documented great hammerheads attacking spotted eagle rays both on the bottom and at the surface. The hammerhead’s wide, flattened head is thought to help pin rays against the seafloor during these encounters.

Bull sharks and tiger sharks also prey on spotted eagle rays opportunistically, though neither specializes in rays the way hammerheads do. The barbed venomous spine on the eagle ray’s tail provides some defensive capability, but it is not always enough to deter a determined large shark. Juvenile eagle rays face additional threats from a wider range of predators simply because of their smaller size.

Feeding Eagle Rays in Captivity

Spotted eagle rays are popular exhibit animals in large aquariums, and their diet in captivity generally mirrors their wild preferences. In one well-documented case at a large public aquarium, two eagle rays were maintained in a display tank of over 21 million liters and hand-fed live clams by divers on SCUBA. The rays developed aggressive behaviors toward the divers during feeding, bumping and pursuing them, which prompted a training program using conditioning techniques. The rays learned to station at a target to receive food and to transfer between different divers on cue, which resolved the behavioral issues and demonstrated that these animals are capable of learning feeding-related tasks.⁸

Aquariums typically offer a rotating diet of clams, squid, shrimp, and sometimes small fish, though the rays consistently show the strongest feeding response to hard-shelled items they can crush. Keeping their tooth plates healthy requires regular access to hard prey; without it, teeth can overgrow or wear unevenly. This is one of the practical challenges of maintaining eagle rays in captivity and a reminder that their crushing diet is not just a preference but a physiological necessity tied to the way their teeth grow and are replaced.

An Ancient Adaptation for Hard Prey

The shell-crushing lifestyle of spotted eagle rays is not a recent evolutionary experiment. Fossil tooth plates from ancestral myliobatid rays, the family that includes eagle rays and their relatives, document the emergence and diversification of durophagy over millions of years. A fossil species described as having a body plan intermediate between bottom-dwelling stingrays and the more streamlined, open-water eagle rays supports the idea that the shift to crushing hard-shelled prey went hand in hand with the evolution of the eagle ray’s distinctive wing-like body shape and pelagic swimming style.⁹

In other words, the ancestor of today’s eagle rays was likely a benthic ray that ate softer prey. As crushing jaws and flat tooth plates evolved, these rays gained access to a rich and previously underexploited food source: shellfish beds. The energy payoff from cracking into densely caloric bivalves and gastropods may have favored larger body sizes and more powerful swimming, eventually producing the broad-winged, open-water foragers we recognize as eagle rays today.⁹ The entire body plan of a spotted eagle ray, from its fused snout to its massive pectoral fins to its flat grinding teeth, can be read as an integrated toolkit for finding, excavating, and crushing shellfish. Few marine predators are so thoroughly committed to a single style of feeding.