The largest fish in the sea lives on some of the smallest animals in it. Whale sharks filter zooplankton — shrimp, copepods, krill, fish eggs, and crab larvae — along with small schooling fish such as anchovies, and they can only do it profitably where that food is packed unusually densely. This guide draws on Whale Sharks: Biology, Ecology, and Conservation, the first scientific textbook on the species, whose feeding chapter was written by MMF scientists Chris Rohner and Clare Prebble.
What do whale sharks eat?
Whale sharks eat plankton and small fish. The recurring items across every studied population are copepods (tiny crustaceans, usually under 2 mm), sergestid shrimp, euphausiid krill, crab and other decapod larvae, arrow worms, and fish eggs — plus anchovies and other small schooling fish where they are available.
The prey list changes from place to place, and what matters is not the species but the density. Off Mafia Island in Tanzania, our team sampled the water beside feeding sharks and found the plankton was about ten times denser than the surrounding sea — 25 milligrams of plankton per cubic meter against a background of 2.6. In those dense patches a single large sergestid shrimp, Belzebub hanseni (long known as Lucifer hanseni), made up roughly half of everything we identified. In the background water, small copepods dominated instead. So the sharks were feeding in dense patches that happened to be dominated by one shrimp. Whether they were picking out that shrimp or simply filtering whatever was in the thickest water is not something plankton samples taken beside a feeding shark can settle — prey density and prey composition change together.
Elsewhere the pull is fish spawn. Whale sharks gather at offshore oil and gas platforms in Qatari waters of the Arabian Gulf, where our colleague David Robinson and MMF scientists documented more than 400 sharks feeding on tuna eggs — a food supply that can run for months rather than days. Tracking work around the same platforms in 2025 showed individual sharks staying in the area for weeks at a time. Off the Yucatán coast of Mexico, the same trick draws the biggest known gathering of the species: up to 420 whale sharks feeding in an 18 square kilometer patch of tuna spawn, a figure carried into the current IUCN Red List assessment.
There is also a list of things found in whale shark stomachs that look more like by-catch than a meal: jellyfish, pteropod snails, seaweed, and — in one Indian record from the 1950s — gastropod shells. Some of that is demonstrably accidental; we have watched a shark spit out a jellyfish it had inadvertently sucked in. Other items sit in a middle category. Arrow worms, for instance, are a normal part of the surface plankton whale sharks filter, so they are genuine minor prey rather than mistakes — just unlikely to be what a shark is aiming for. Filter feeding is not precise.
How does a whale shark filter its food?
Water goes in the mouth, passes over 20 filter pads, and leaves through the gill slits. The food stays behind. The pads are modified gill rakers — a flattened mesh with holes about a millimeter across, quite unlike the comb-like rakers of a basking shark.
The leading explanation for how food is separated is crossflow filtration: water runs along the pads rather than straight through them, so particles are swept toward the back of the throat in suspension while the water exits over the gills. That neatly explains why the filters do not clog in dense prey patches. It does not explain everything. Whale sharks routinely swallow fish eggs smaller than their own mesh pores, and nobody yet knows how. When the pads do foul, the shark can cough to backflush them and spit the debris out through its mouth.
Our guide to whale shark anatomy covers the mouth, filter pads, and gill chamber in more detail. The short version: the feeding apparatus takes up close to a third of the animal’s body length, and the throat behind it is only about the width of a baseball.
What are the three ways whale sharks feed?
Passive (ram) feeding, active surface feeding, and stationary suction feeding. Most filter-feeding sharks only manage the first — open the mouth and swim. Whale sharks can also actively suck water in, and that is what gives them the other two modes.
Passive, or ram, feeding. The shark swims slowly forward with its mouth partly or fully open and lets its own motion push water through the filters. This is the cheapest mode and the one used when prey is thinly spread or too small and slow to escape — fish eggs, for instance. It works at the surface or at depth.
Active surface feeding. The shark swims forward while rapidly expanding its mouth and gill basket, gulping as it goes. The dorsal fin, the top of the head, and the upper jaw often break the surface. This is the behavior most people photograph, and it is what whale sharks switch to when prey is dense or fast-moving. At Mafia Island, 87% of the feeding we recorded was active surface feeding — unsurprising, given that the target was a 10 mm shrimp capable of darting away from an approaching mouth.
Stationary, or vertical, suction feeding. The shark stops swimming, lets its tail sink, hangs nose-up near the surface, and pulls water in by suction alone, creating a vortex that draws prey to it. Mexican guides call these sharks botella — bottles — because that is exactly what a vertically hanging whale shark looks like. It is used on small, tightly concentrated patches and on small fish.
There is a fourth variant worth knowing. At Mafia Island, sharks chasing sergestid shrimp use “yo-yo feeding” — repeated shallow bounce dives in the top 10 meters that appear to trap fleeing prey against the underside of the sea surface.
The trade-off in all this is that active suction filters less water than passive ram feeding does. Whale sharks buy access to mobile prey at the cost of throughput, which is exactly why they depend on finding dense patches.
How much does a whale shark eat, and how much does feeding cost?
The only published estimates come from two juveniles in Mexico: a 6.6 m shark taking in about 28,000 kilojoules a day and a 4.4 m shark about 15,000. Read those as an order-of-magnitude sketch, not a species average — nobody has measured intake for a typical whale shark, let alone an adult.
Set against modeled resting metabolic costs, both were comfortably in profit while the aggregation lasted — a net gain of roughly 11,000 and 8,000 kilojoules a day respectively. That calculation depends on estimated body masses and modeled metabolic rates, each carrying real uncertainty, and it describes two juveniles at one exceptionally good feeding site.
You may see a claim that whale sharks filter around 600,000 liters of water an hour. We have not been able to trace that number to any study, and it does not appear in the scientific literature on whale shark feeding. Treat it as folklore.
What is better established is that feeding is expensive. An open mouth wrecks a whale shark’s streamlining, and the extra energy cost of feeding rather than simply swimming is more than three times higher at the surface than it is below it — surface feeding means fighting drag at the air–water boundary as well. So whale sharks do not feed on everything they pass through. Off Mafia Island the switch from searching to feeding happened at roughly 12 milligrams of dry plankton per cubic meter, close to the threshold measured for reef manta rays using the same method. A basking shark, which filters passively and continuously, will feed in considerably poorer water. We would not put a number on the size of that gap: the published basking shark and whale shark thresholds were measured in different ways — one as wet weight of plankton, the other as dry weight — so they are not directly comparable. The qualitative conclusion stands, and it follows from anatomy: an actively suction-feeding shark needs richer water than a passive filterer does.
The flip side of a high threshold is that whale sharks must go hungry between opportunities. Aquarium sharks routinely fast for up to eight days at a time, and blood chemistry suggests long fasts are normal for wild sharks on oceanic crossings. Feast and famine is the working model for the species. One much-repeated extreme needs its context restored: the aquarium shark that did not feed for 151 days did so in the period before it died. That is not evidence of how long a healthy whale shark can go without food.
Do whale sharks feed at night or in deep water?
Almost certainly both, and this is where the surface photographs mislead us most.
The strongest evidence comes from MMF’s work in Mozambique. Combining stomach contents from stranded sharks with fatty-acid signatures from living ones, we found that Mozambican whale sharks are not living on daytime surface plankton alone. Three of the stomachs we examined were dominated by mysids — small shrimp-like crustaceans that spend the day in the seabed and rise into the water column only after dark. In one stomach they were 61% of the prey items, in another 92%. Mysids that behave that way are not available to a shark feeding in daylight. That is direct evidence of night feeding.
The deep-water part of the story is weaker, and worth keeping separate. The fatty acids in whale shark tissue are strange: arachidonic acid, an omega-6 fat, made up about 18% of the total in our Mozambican sharks, while the surface plankton they were seen eating was dominated by omega-3 fats instead. The profiles resembled those of deep-living shrimp, mysids, and lanternfish. That suggests whale sharks also forage hundreds of meters down, which fits their diving behavior — they reach depths well beyond a thousand meters, as covered in our guide to whale shark movements. But a fatty-acid resemblance is a hint, not a stomach. Rival explanations are still live, including that whale sharks route particular fats preferentially into the skin tissue researchers can actually sample, or that long fasts distort the signal. Our textbook leans toward a physiological explanation; the question is genuinely open.
Does every whale shark eat the same thing?
No — and the differences run at the level of the individual animal. Mafia Island’s whale sharks are unusually resident and unusually well catalogued, which let us sample the same identified sharks over several years. Those stable isotope data show a range of individual feeding strategies within one small aggregation, with differences related to sex and body size, even though the population as a whole occupied a fairly narrow feeding niche.
In other words: the sharks at one site are all plankton eaters working the same local food web, but some specialize more than others. Size and sex differences are a recurring theme across whale shark diet studies, and they matter because coastal feeding sites are heavily biased toward juvenile males. What large adults and newborn pups eat is still substantially unknown. One long-standing hypothesis is that adults shift onto larger prey — the small midwater fish that swarm hundreds of meters down in the open ocean. That would give them a steadier food supply than juveniles chasing short-lived plankton patches, and it might help explain how they grow so large. It has not been tested.
Why do whale sharks gather in the same places every year?
Because a handful of places reliably concentrate food, and whale sharks appear to remember them. At least 30 coastal hotspots have now been identified worldwide, and at most of them shark presence tracks prey availability.
Some are driven by a biological event with a calendar: a fish spawning aggregation, as in Qatar and Mexico. Others are built by physical oceanography — upwelling, river run-off, wind, and currents combining to pile zooplankton into patches. Individual sharks show real fidelity to these sites, returning across years and sometimes decades, and rarely turning up at a second aggregation.
The striking part is that they sometimes arrive early. At Mafia Island we have watched sharks show up weeks before any feeding is observed, searching rather than feeding, apparently waiting for the patches to form. Smell almost certainly does the close-range work: captive whale sharks will start feeding in response to chemical cues alone — krill homogenate, and to a lesser degree dimethyl sulfide, a compound phytoplankton release when zooplankton graze on them, which is an indirect signal that dense zooplankton is present. But that only helps within a prey patch, not from hundreds of kilometers away, so the early arrivals look like learned, remembered timing — a form of spatial memory nobody has yet studied properly in the species. Between those events, the same sharks cross thousands of kilometers of open ocean; see our guide to whale shark movements for where they go.
Do whale sharks eat plastic?
Yes, unavoidably. An animal that filters cubic meters of water for millimeter-scale food cannot exclude millimeter-scale plastic.
MMF’s work in Indonesia measured the exposure directly: whale sharks feeding in Javanese coastal waters were passing through water carrying up to about 137 pieces of plastic per hour of filtering. Our colleague Elitza Germanov and co-authors later confirmed the sharks are ingesting it, finding microplastics in whale shark fecal samples in the Philippines. Whale sharks also swallow larger items, with fatal results in several documented cases — a hardened plastic straw that punctured the gut in Thailand, a plate lodged in the stomach outlet in Japan, a bag obstructing the intestine in Malaysian Borneo.
Two caveats keep this honest. First, whale sharks do exercise some choice: we have seen a shark spit out a large piece of plastic it had inadvertently sucked in, and react the same way to an accidentally ingested jellyfish. Big items can be rejected; microplastics cannot. Second, the population-level consequences are unquantified. Plastic overlaps whale shark habitat almost everywhere and the potential harms are real — gut damage, and chemicals carried on plastic surfaces — but the Red List assessment classes the threat as data deficient rather than demonstrated. It is a research priority, not a settled cause of decline. Our guide to threats sets it beside fishing and ship strike.
Are whale sharks dangerous to swimmers?
No. A whale shark’s throat is roughly the width of a baseball, its thousands of teeth play no part in feeding, and it lives on plankton and small fish. There has never been a case of a whale shark preying on a person. The risk in the water runs the other way — toward the shark, from boat propellers and from swimmers crowding or touching it. See our whale shark facts page and swim with whale sharks for how a good encounter is run.
What happens when people feed whale sharks?
Whale sharks learn fast, and feeding them changes them. At Oslob in the Philippines, sharks are hand-fed shrimp from small boats and will hold a vertical suction-feeding posture for hours. Aquarium sharks have been trained to follow particular colored ladles. In Cenderawasih Bay, Indonesia, wild sharks have learned to work fishers’ lift-nets at night, sucking baitfish straight out of the mesh.
The Oslob evidence, reviewed in our textbook, shows sharks that associate the site with food, stay longer than they otherwise would, become habituated to close human contact, and carry far more scarring than sharks at non-provisioned tourism sites. Provisioning also raises the energy a shark spends while it is there. Whether the local economic benefits justify those costs to the animals is unresolved, and it is an ethical question as much as a scientific one. It is why MMF supports tourism built on natural feeding aggregations rather than hand-feeding.
Why it matters for conservation
Feeding is what makes whale sharks findable, and therefore protectable. The coastal aggregations where they come to eat are the places we can count them, identify them, measure them, and detect decline — the 87% drop in sightings we recorded off southern Mozambique was only visible because that site is a feeding site. Those same aggregations are where sharks are most exposed to boats, nets, and plastic, and they are small enough to be managed. Knowing which patch of water matters, in which month, and why, is what turns a general concern about an Endangered species into a protected area with lines on a map.
Feeding is also how whale sharks act on the ocean rather than just in it. They take up large amounts of plankton in warm, generally unproductive waters, then carry it — as body mass, waste, and eventually carcass — across thousands of kilometers and hundreds of meters of depth. Our textbook’s reading is that this makes them a nutrient vector, moving energy between rich and poor parts of the ocean, by analogy with baleen whales. Nobody has yet measured that budget for whale sharks.
You can help fund that work by adopting a whale shark.