Sharks: What Do They Eat? A Look at Their Diverse Diets

Sharks eat everything from microscopic plankton to whales, and the roughly 500 known species occupy nearly every feeding niche the ocean has to offer. The popular image of a shark is a sleek predator tearing into a seal, but that describes only a handful of species. Most sharks are actually smaller, bottom-associated predators that eat fish, crabs, and squid, and a few don’t hunt at all, instead filtering seawater for tiny organisms. Understanding what sharks eat means appreciating a group of animals that has diversified its diets over hundreds of millions of years in ways that still surprise researchers.

Most Sharks Are Not Apex Predators

One of the biggest misconceptions about sharks is that they sit uniformly at the top of the food chain. In reality, the majority of shark species function as mid-level predators. Among the 73 shark species documented in the eastern North Pacific alone, fewer than half reach maximum lengths greater than about two meters, and roughly 78% live on or near the seafloor of the continental shelf or slope rather than cruising the open ocean.¹ These smaller, bottom-dwelling species tend to eat small bony fish and crustaceans like crabs and shrimp. Even on coral reefs, where sharks are often cast as the top-down enforcers of ecosystem order, most reef-associated species turn out to be mesopredators, feeding alongside a wide range of reef fish rather than sitting above them.²

That said, several truly large, open-ocean species do earn their reputation. White sharks, shortfin makos, and some requiem sharks hunt large fish, marine mammals, and even other sharks. The twist is that even among these big predators, diet changes drastically over a lifetime, something covered in detail further on.

Filter Feeders and the Largest Sharks on Earth

The two largest fish in the ocean, the whale shark and the basking shark, eat some of the smallest prey. Rather than chasing down individual animals, they filter enormous volumes of seawater to extract plankton and tiny fish. Whale sharks off Mexico’s Yucatan Peninsula have been observed spending about seven and a half hours per day feeding at the surface on dense patches of plankton dominated by small crustaceans, arrow worms, and fish larvae. A whale shark roughly four and a half meters long can filter around 326 cubic meters of seawater per hour; a six-meter individual manages about 614 cubic meters per hour.³ At average plankton densities at those feeding sites, that translates to roughly 1.5 to 2.8 kilograms of plankton consumed per hour.

These sharks use a method called ram filter feeding: they swim forward with their mouths open, forcing water over a filtering apparatus in their gills. Research on whale sharks has revealed that their filters use a cross-flow mechanism rather than a simple sieve. Water moves across the filter pads at an angle, concentrating food particles while reducing clogging, which allows the sharks to capture plankton even smaller than the actual mesh size of the filter.³ Basking sharks feed similarly, cruising slowly through plankton blooms with their mouths agape. Despite their enormous size, both species are harmless to humans and to virtually every animal larger than a thumbnail.

The Generalists

Tiger sharks are the textbook example of a shark that will eat almost anything. Stomach content studies and chemical analysis of their tissues both show that tiger sharks are generalist feeders at the population level, consuming fish, sea turtles, seabirds, marine mammals, crustaceans, and even garbage.⁴ That reputation for eating just about anything is well documented: researchers have pulled license plates, tires, and pieces of armor from tiger shark stomachs over the decades. Their broad, serrated teeth are well suited for cutting through a range of prey, from soft-bodied squid to the hard shells of sea turtles.

White sharks, despite their reputation as precision seal-hunters, are more opportunistic than they’re given credit for. DNA-based analysis of the gut contents of over 200 juvenile and subadult white sharks from eastern Australia found diets consisting primarily of ray-finned fishes, including mullets, jacks, and mackerel, along with smaller amounts of other sharks, marine mammals, and even seabirds.⁵ Young white sharks, it turns out, are primarily fish-eaters; the dramatic seal-hunting behavior shows up later in life. Scavenging also plays a role. White sharks have been documented feeding on whale carcasses, and researchers have proposed that whale scavenging may be a more significant part of their overall diet than previously appreciated, especially as they approach sexual maturity and need far more calories.⁶

Hard-Shell Specialists

Not every shark has the blade-like teeth you see in nature documentaries. Some species have evolved flattened, molar-like teeth designed for crushing hard-shelled prey, a feeding style called durophagy. The bonnethead shark, a small member of the hammerhead family, feeds almost exclusively on hard-shelled crabs. It captures crabs by ramming into them, then crushes the shells between specialized molariform teeth before swallowing. This shell-crushing mechanism involves a distinct jaw movement: the jaw adductor muscles stay active through a second closing phase, applying sustained force in a way that ordinary bite-and-swallow feeding does not require.⁷

Horn sharks take a similar approach, crunching through sea urchins and other hard-bodied invertebrates on the rocky reefs they call home. Young horn sharks face a real challenge, though. Bite force scales with body size, and smaller individuals simply can’t generate enough force to crack the hard prey that adults eat regularly. A fully grown horn shark can generate posterior bite forces exceeding 380 newtons, but a juvenile may produce only 15 newtons, far too little to break open all but the smallest urchins.⁸ Their jaw mechanics grow disproportionately fast relative to body size, allowing them to start eating hard prey earlier than you’d expect from their size alone, but they’re still functionally locked out of the adult diet for much of their early life.

The Parasitic Feeder

The cookiecutter shark is one of the strangest feeders in the ocean. Barely half a meter long, it takes neat, round plugs of flesh out of animals many times its size, including tuna, dolphins, whales, and even other sharks. Its lower jaw is equipped with a row of broad, interconnected teeth that function together like a cookie cutter pressed into dough. Upper teeth are narrower and shorter, anchoring the shark in place while the lower jaw rotates to scoop out a nearly symmetrical oval of tissue.⁹ The resulting wound is distinctive and has been found on a wide range of species.

Research around an equatorial Atlantic archipelago found that cookiecutter sharks target adult fish across most species, efficiently removing energy-rich tissue layers, though their approach to yellowfin tuna differs: they preferentially attack juveniles, possibly because younger tuna swim at depths that overlap more with the shark’s range. Bites predominantly land on the lateral body in most prey species, but on yellowfin tuna, about 95% of bites targeted the ventral region.¹⁰ This is ectoparasitic feeding rather than predation: the prey animal usually survives, though scarred.

The Shark That Eats Its Vegetables

For years, marine biologists noticed seagrass in bonnethead shark stomachs but assumed it was swallowed incidentally while the sharks were hunting crabs in seagrass beds. That assumption was wrong. A 2018 study showed that bonnetheads actually digest seagrass with roughly 50% efficiency for organic matter, a figure comparable to some sea turtles. Chemical analysis confirmed that carbon from seagrass was being assimilated into the sharks’ tissues, not just passing through.¹¹ Researchers also detected cellulose-degrading enzyme activity in the sharks’ hindguts, suggesting that gut microbes help break down the plant material.¹²

This makes the bonnethead the first known omnivorous shark. It challenges the assumption that all sharks are obligate carnivores and has ecological implications as well: a shark that grazes seagrass may transport nutrients between seagrass habitats and open water in ways that no one had accounted for. Whether other shark species also digest plant matter remains an open question, but the bonnethead at least proves the possibility.

How Diet Changes as Sharks Grow

One of the most important patterns in shark feeding ecology is that diet shifts as an individual gets bigger. Young sharks eat small, easy-to-catch prey. As they grow, they gain the jaw strength, gape size, and swimming speed to tackle larger and tougher food. Copper sharks, for instance, show a discrete dietary shift at roughly 200 centimeters in total length: individuals below that size eat mainly fish, while those above it begin to prey on other sharks and rays.¹³

White sharks follow a similar trajectory but with higher-profile prey. Juveniles eat mostly bony fish. At around 210 centimeters, structural changes in jaw morphology produce broader teeth and increased bite capacity, supporting a transition from an all-fish diet to one that includes marine mammals.¹⁴ This is not just a matter of preference; it reflects physical thresholds. A young white shark’s teeth and jaws are shaped for gripping slippery fish, not for carving through blubber. As the animal grows, its equipment literally changes shape. Many shark species also segregate their juvenile and adult foraging habitats, which further reduces competition between size classes.¹

Teeth as Dietary Indicators

Because sharks continually grow and replace their teeth, tooth shape is a reliable indicator of feeding strategy. Sharks that eat large prey they need to cut into pieces tend to have broad, serrated, blade-like teeth. Those that swallow prey whole usually have narrow, pointed teeth for gripping. A comparison of two large, overlapping shark species in Australian waters illustrates the difference well. The grey nurse shark has spear-shaped grasping teeth suited for seizing fish and swallowing them intact, while the sevengill shark has multi-cusped cutting teeth used to carve pieces from larger prey.¹⁵ The cutting teeth appear to give the sevengill access to higher-quality prey at a smaller body size than the grey nurse can manage, because it can process prey items that are too large to swallow whole.

Flattened, pavement-like teeth signal a hard-shell diet, as seen in the horn shark and bonnethead. Meanwhile, the tiny teeth of filter-feeding species like whale sharks are vestigial, playing no real role in feeding. If you want a rough guide to what a shark eats, looking at its teeth gets you surprisingly far.

How Sharks Find Their Food

Sharks are famous for their keen sense of smell, but the final moments of a strike depend heavily on electroreception, the ability to detect the faint electrical fields that living organisms produce. Experiments blocking different sensory channels in three shark species found that electroreception is what triggers the jaw to open during a strike. Without it, blacktip and nurse sharks could still capture prey if they happened to touch it with their snouts, though it took repeated attempts. Bonnethead sharks, however, could not capture prey at all when electroreception was blocked, even when they made direct physical contact with the food. Their jaw depression appears to be entirely controlled by the electrical signal surrounding the prey.¹⁶

This means the sensory toolkit a shark uses can vary by species and habitat. Open-water hunters like white sharks rely on a suite of senses in sequence: smell at long range to locate a general area, vision and lateral-line detection at medium range to zero in, and electroreception in the last few centimeters before the bite. White sharks hunting seals near a colony in South Africa were observed to maintain a search base roughly 100 meters seaward of the seals’ primary entry point, apparently balancing prey detection against capture rates and competition with other sharks.¹⁷ Smaller, less experienced sharks showed more scattered search patterns and lower predatory success, suggesting that hunting strategy is partly learned.

What Happens Below the Twilight Zone

Deep-sea sharks occupy a less studied but fascinating dietary world. Stomach content studies of several deep-water species off New Zealand found diets dominated by fish and cephalopods, though the specific prey depended on where the sharks lived in the water column. Species associated with the ocean floor, like the kitefin shark and the leafscale gulper shark, ate mainly bottom-dwelling and near-bottom fish and squid. More mid-water species, like the longnose velvet dogfish, fed primarily on mesopelagic fish and squid that inhabit the dimly lit zone between about 200 and 1,000 meters deep. Across most of these species, the commercially important hoki, a bottom-dwelling fish common in New Zealand waters, turned up as a dominant prey item. Empty stomachs were common, occurring in 8 to 62% of individuals sampled depending on the species, which hints at the feast-or-famine reality of life in the deep ocean where meals can be unpredictable.

Shark Diets and Ecosystem Ripple Effects

Because sharks feed across so many levels of the food web, their presence or absence can reshape entire ecosystems, though the effects are not always what you’d predict. A landmark study of the northwest Atlantic documented that as populations of 11 large shark species declined over 35 years, 12 of 14 smaller elasmobranchs they preyed on increased in abundance. One of those newly abundant species, the cownose ray, ramped up its own predation on bay scallops enough to collapse a century-old scallop fishery.¹⁸

That finding became one of the most cited examples of a trophic cascade driven by shark loss, but subsequent work has complicated the picture. Studies on the Great Barrier Reef found that even a fourfold difference in reef shark density across sites had no measurable effect on the density or biomass of the fish communities below them in the food web.¹⁹ The diversity and complexity of coral reef food webs may buffer against cascading effects when shark numbers drop. In other words, where a food web is simple and a single prey species dominates, losing sharks can have dramatic downstream consequences. Where the web is complex and energy flows through many pathways, the loss may be absorbed. The evidence for shark-driven trophic cascades that directly benefit corals remains weak and contested.²

Shark-Feeding Tourism and Whether It Changes Diets

Shark-diving tourism often involves chumming the water or directly feeding sharks bait to attract them for tourists. A reasonable concern is whether this alters the animals’ natural diets or creates dependency. Stable isotope analysis of bull sharks at a provisioning site found no evidence that the food handed out by dive operators was being incorporated into the sharks’ tissues, even among individuals that showed up regularly to eat the handouts.²⁰ The amount of food provided at typical tourism sites appears to be a small fraction of a bull shark’s total intake, not enough to shift the dietary signal.

The more unexpected finding is what happens to the other fish at these sites. Observations at shark-feeding dives showed that a wide range of coral reef fish, spanning multiple families and feeding strategies, take advantage of the food scraps that scatter when sharks feed. Herbivorous fish that would normally eat algae, planktivores that normally eat tiny drifting organisms, and various other species all jumped at the chance for a free meal.²¹ In this sense, shark-feeding tourism may have a greater dietary effect on the bystander reef fish than on the sharks themselves.

What Shark Diets Mean for Mercury Levels

Because many sharks are high-level predators that eat other predators, they accumulate heavy metals, especially mercury, at concentrations far above what’s found in their prey. Blue sharks off the Pacific coast of Mexico had average mercury levels in muscle tissue of about 1.4 micrograms per gram of wet weight, above the 1.0 microgram per gram threshold commonly used as a safety guideline for human consumption. Their primary prey, pelagic red crabs, contained only 0.04 micrograms per gram, illustrating how dramatically mercury concentrates as it moves up the food chain.²² This process, called biomagnification, is why public health agencies generally advise limiting consumption of shark meat.²³

Mercury levels vary by species and region, but as a rule of thumb, the higher a shark feeds in the food web and the longer it lives, the more mercury it will carry. A whale shark filtering plankton would carry far less than a mako shark eating tuna. For anyone eating shark meat, whether as a delicacy or as a staple protein in coastal communities, this is the most direct way that shark diet translates into a human health concern.

Ancient Megatooth Diets

The dietary ambitions of sharks have a deep evolutionary history. Otodus megalodon, the massive megatooth shark that went extinct roughly three million years ago, occupied an extremely high position in the food web, likely higher than any marine predator alive today. Nitrogen isotope analysis of fossil tooth enamel suggests that as the megatooth lineage evolved toward gigantic body sizes, its dietary position shifted upward, meaning each successive species was eating prey that was itself a predator. The highest feeding level was apparently reached before peak body size, suggesting that diet drove size evolution rather than the other way around.²⁴ Modern white sharks, sometimes considered a living analogue of megalodon, actually feed at a considerably lower level by comparison.

Shark guts themselves reflect millions of years of dietary adaptation. The spiral intestine, a corkscrew-shaped structure found in all sharks, skates, and rays, slows the passage of food and increases the surface area available for nutrient absorption. Recent work using 3D imaging found that these spiral intestines function somewhat like Tesla valves: they permit flow in one direction far more easily than the other, creating a passive, one-way movement of digested material that requires little muscular effort.²⁵ Interestingly, the shape of the spiral intestine does not correlate with diet type, meaning filter feeders and active predators can have similar gut architectures. The spiral intestine seems to be a versatile, energy-efficient solution to digestion rather than a specialized tool for any particular food source.