Whale sharks can grow to 60 feet long and have mouths easily big enough to swallow a human.
Far from being vicious predators, however, whale sharks are gentle giants that drift around the ocean feeding on microscopic prey and the occasional fish.
What do Whale Sharks Eat?
Whale sharks live on a diet of tiny planktonic organisms. A diverse collection of organisms make up this plankton, all of which are so small they’re “unable to propel themselves against a current.”
Plankton includes krill, crab larvae, and microscopic jellyfish. It also contains some plant matter in the form of algae.
Although whale sharks have long been believed to live “almost exclusively on animal protein,” a study published in the Ecological Monographs journal in 2019 found that these gentle giants might have “a pretty omnivorous diet that includes plants and algae.”
Whale sharks are predominantly filter feeders, so can’t be too selective about what they eat.
Filtering pads extract small particles and plankton as the water pours through their gills.
This feeding method “discriminates particles by size, not by species,” leaving the whale shark with little choice about how it gets its nutrition.
In addition to plankton, whale sharks also prey on small fish, like sardines and anchovies. They will charge into a ball of baitfish, ramming as many fish into their mouths as possible as they rush through the ball.
Scientists are unsure of how frequently whale sharks choose to feed like this. Although whale shark gets a bigger meal, this feeding method requires more energy than the whale shark’s more leisurely passive feeding techniques.
The Whale Shark Diet
The whale shark diet is more varied than you might initially expect.
Scientists believed that whale sharks lived on a diet of plankton alone for a long time, but recent studies suggest that they also eat algae, small schooling fish, and even the occasional squid.
Despite that, a study of whale sharks off the coasts of Mozambique and South Africa discovered that small, shrimp-like crustaceans known as mysids formed the bulk of the sharks’ diet, making up 61 to 92% of the stomach contents of three stranded whales.
Other studies found that crab larvae form a critical part of the whale shark’s diet and that older whale sharks tend to seek out larger prey species, targeting more “small fish and/or larger zooplankton of higher trophic level … as they grow.”
Whale sharks are limited in what they can eat because they can’t chew, and their throats are quite small.
How Much do Whale Sharks Eat?
Whale sharks are highly mobile and migratory, covering thousands of kilometers a year.
This behavior makes it impossible for researchers to follow them around, trying to figure out how much they eat. Fortunately, there are some very clever scientists out there who came up with a way of working it out.
Researchers studying the feeding anatomy, behavior, and diet of the whale shark off Cabo Catoche, Yucatan Peninsula, Mexico, made some interesting discoveries.
They calculated that whale sharks spend around 7.5 hours eating per day. During that time, a shark measuring 19.6 feet in length takes around 600 cubic meters of water into its mouth every hour.
From that, it filtered out approximately 2.8 kg of food per hour, meaning it consumed 21 kg of food per day.
That’s for a 19.6-foot shark, however. The largest whale shark ever recorded measured 61.7 feet, so we can assume it would need to eat three times as much as a smaller shark, making its daily consumption as much as 60 kg!
Whale sharks probably don’t consume this much daily, and scientists suspect they go through periods of prolonged fasting. Studies show that whale sharks can “go for four months or more without eating.”
This approach would make sense for a highly migratory creature. When there’s food in abundance, it gorges itself and then uses that energy to sustain itself while searching for the next meal.
How do Whale Sharks Hunt for Food?
Researchers believe that whale sharks use their sense of smell to locate their prey. They “can sense the density of plankton with their nostrils” and then direct their massive heads accordingly.
Whale sharks have several different feeding methods, which they utilize for different types of prey and situations.
Whale sharks can feed while completely stationary, sucking in the plankton by repeatedly opening and closing its mouth.
When suction feeding, the whale shark can be either vertical or horizontal in the water but is virtually motionless for the duration.
When surface ram feeding, a whale shark will swim at the surface of the water with the top of its head exposed. The open mouth is also partially out of the water as the shark swims slowly at speeds of around 0.3–1.5 m/s.
As it moves, it rams water and plankton into its mouth and through its filtering apparatus.
When ram feeding, the whale shark occasionally “coughs” to flush water and particles out of its filters before it resumes feeding.
Whale sharks use a similar technique underwater in a feeding method known as sub-surface passive feeding.
When targeting small fish, whale sharks use a technique similar to the surface ram feeding method but travel faster and more aggressively, bursting into a ball of baitfish. They will also hang vertically underneath a baitball, hoovering fish into their mouths.
Unfortunately, these feeding methods put whale sharks at risk of consuming waste plastic and other marine pollution.
Marine biologists from the Marine Megafauna Foundation at Australia’s Murdoch University teamed up with researchers from Udayana University in Indonesia to calculate how much plastic whale sharks could be ingesting.
They concluded that it could be as much as 137 pieces of plastic per hour!
Ingesting this much plastic could negatively impact the already threatened species, especially given how slowly whale sharks reproduce.
What Animals Compete for Food with Whale Sharks?
Whale sharks aren’t the only filter feeders in the ocean, and plankton is “a crucial source of food to many small and large aquatic organisms.”
Basking sharks are large filter feeders similar to the whale shark and are, therefore, most likely to compete with the whale shark for food.
Basking sharks travel thousands of kilometers in their search for food, so the habitat of the two species could easily overlap.
Other large filter feeders, like the blue whale and the megamouth shark, will also utilize tropical waters, potentially competing with whale sharks for the same microscopic organisms.
FAQ
What is a Whale Shark’s Favorite Food?
Whale sharks can’t necessarily choose what they’re going to eat as they often use a passive feeding technique.
When given the option, however, they will seek out areas with a high concentration of planktonic organisms, including crab larvae, krill, and jellyfish.
Do Whale Sharks Eat Jellyfish?
Whale sharks do eat tiny jellyfish, but they won’t predate larger species that require chewing.
Is a Whale Shark a Carnivore?
Although researchers long believed the whale shark to live off animal protein alone, recent studies suggest that it has more of an omnivorous diet, consuming plant matter in the form of algae alongside zooplankton and small fish.
What do Whale Sharks Not Eat?
Whale sharks cannot eat anything that requires chewing, so consume only microscopic plankton and small fish. They do not prey on larger fish, marine mammals, or humans.
Conclusion
Whale sharks have a more varied diet than researchers suspected, eating algae and small fish in addition to plankton.
They also have a wider array of feeding methods than scientists initially thought, using ram filter feeding, in addition to more passive techniques.
The whale shark’s anatomy makes it impossible for it to chew or swallow larger species, so although it is the biggest shark in our oceans, it’s also one of the least aggressive.
Nicky is a British adventurer and animal lover who spends her time exploring the natural world and writing about her experiences. Whether on horseback, underwater, running, hiking or just standing with a fishing rod in hand, she embraces everything her adopted home of South Africa has to offer.