The basking shark (Cetorhinus maximus), is the second largest shark and fish species in the world. They are also one of the three plankton eating sharks. The insides of a basking shark’s mouth is lined with gill rakers that filter plankton from the water it intakes. Despite their enormous size, basking sharks are harmless to humans, but humans have been harmful to them. Due to the shark’s sometimes elusive nature, some of their traits and behaviors leave scientists stumped.
1. One basking shark can filter 4,000,000 pounds of water in only one hour while filter feeding
Basking sharks weigh nearly 10,000 pounds, but plankton is microscopic. So in order for a basking shark to survive, it needs to eat hundreds of pounds of zooplankton every day. In just one hour of feeding, a single basking shark can filter 4,000,000 pounds of water. Usually, the shark will keep its mouth open for a minute at a time. Basking sharks close their mouths to swallow, and then open wide for more food.
2. Basking Sharks have open jaws that are one meter wide, and teeth less than ½” big
As some of the largest fishes, basking sharks also have some of the largest jaws. A basking shark’s jaw is usually around 1.2m wide (3.9ft). These huge jaws make the shark look like you just told it a shocking secret while it's feeding. They also have very small, hooked teeth. These teeth are only one fifth of an inch, or 5mm. For reference, the smaller great white shark has teeth as big as 6.6” or 167mm.
While their jaws are big enough to swallow a human, basking sharks avoid large objects when feeding
Despite their enormous size, basking sharks do not attack humans. These animals are actually quite shy. They tend to avoid divers and other large objects while feeding. Photographer Charles Hood says that basking sharks sometimes seem like they are coming right at him, but they always veer away at the very last minute. Even though basking sharks don’t attack, their skin is very rough, so divers know not to touch them.
3. Out of all shark species, basking sharks have the smallest brains relative to their size
Pound for pound, basking sharks have the smallest brains of any shark species. Luckily, basking sharks don’t have to rely on their wits for hunting, and they are large enough that they don’t have to outsmart any predators. Shark photographer Charles Hood noted that he often sees the same sharks when filming, but they never recognize him.
4. The average basking shark is 26ft long and weighs almost 10,000 pounds
The basking shark is the second largest species of fish in the world. Only the whale shark is bigger. Basking sharks grow between 23-28ft, with 26ft being the average length. A few sharks have reached over 33ft, but that is incredibly rare. These long sharks are obviously quite heavy too. The average basking shark weighs 9,300lbs (4218kg). Males are usually larger than females, but reach maturity at a much smaller size.
Some Basking Sharks are over 40ft long and weigh 38,000 pounds
Even though the average basking shark is 26ft long, they can grow much bigger. Beachgoers in New England were stunned to discover a 40ft basking shark swimming in shallow waters. This shark weighed 19 tons, or 38,000 pounds! Basking sharks have a dorsal fin that looks a lot like a great white’s dorsal fin. Beachgoers must’ve been terrified, thinking they were swimming with a 40ft great white! Luckily, it was a docile basking shark.
5. The basking shark’s oil-filled liver accounts for 25% of its body weight
Basking sharks have huge livers that account for 25% of their body weights. A basking shark’s liver runs through its entire abdominal cavity. This liver is rich in squalene. Squalene is an oil that helps sharks that live in deep waters maintain buoyancy. Basking sharks can live as deep as 910m below the surface, but migrate upwards to feed. The liver keeps the shark afloat without the shark exerting too much energy.
6. Basking sharks are filter feeders that eat zooplankton
Basking sharks are filter feeders. This means they feed by opening their mouths and intaking zooplankton, which are microscopic animals like fish, krill, and larvae. Zooplankton usually floats along the ocean surface, because it feeds on phytoplankton, which needs sunlight for photosynthesis. On sunny summer days, basking sharks swim along northern coasts with their mouths wide open, taking in all the zooplankton.
7. The basking shark has bony-looking gill rakers in its mouth to catch plankton
Basking sharks feed with their mouths’ wide open, but they don’t swallow all that saltwater with their food. As the shark swims, water passes through the gills, which you can see along the sides of the shark’s head. Gill rakers are inside the shark’s mouth. The rakers catch zooplankton while the water passes through the gills. This way, the shark doesn’t lose its food with the exiting water.
It is the only shark that passively passes water over its gills
Out of all the filter feeding sharks, the basking shark is the only species that does not need to suck in water to catch its prey. The shark stays passive. The gills and gill rakers filter the water and food, so the shark gets fed just by keeping its mouth open. The whale shark and megamouth shark are also filter feeders. But to feed, they have to use the muscles in their head to suck in water.
8. Basking sharks shed their gill rakers, but scientists aren’t sure why
In summer, basking sharks skim the ocean surface for food. But scientists aren’t certain what these sharks do in winter. Scientists know that basking sharks shed their gills, but don’t know what they do until they regrow. One theory states that the sharks hibernate in winter until the rakers grow back. Another states that they feed on creatures at the bottom of the ocean floor. Scientists are also unsure how often the rakers shed, and how long it takes for them to regrow.
9. Basking sharks shake off parasites by leaping out of the water like whales or great whites
Even though basking sharks are slow swimmers, they breach the ocean surface like their much faster relatives. It’s not known for certain why basking sharks jump out of the water. Unlike great white sharks, they don’t have to jump to catch escaping prey. Scientists believe that basking sharks breach to shake parasites, like lampreys, off their skin.
10. Basking sharks sometimes feed in groups of 100
Basking sharks may not be the most outgoing with humans, but they are very social with their own species. These sharks sometimes feed in groups of over 100 sharks. Scientists aren’t sure why these huge pods develop. But one popular theory is that they get together for courtship rituals to find mates.
11. Basking shark eggs hatch inside the mother
Scientists believe that basking sharks are ovoviviparous, like some amphibians. This means that the female’s eggs are fertilized inside the female. But the female does not lay eggs and wait for them to hatch. Instead, a female basking shark carries the eggs in her body until they are ready to hatch. Once they hatch, she gives birth.
Newborn basking sharks are already 4.5-6ft long
When basking sharks are born, they are already between 4.5’ and 6’ long! These baby basking sharks are huge, but still have a lot of growing to do! Basking sharks might not reach maturity until they are between 16-20ft long. This takes females between 12 to 16 years.
12. Female basking sharks are pregnant for at least 3 years
Considering how big basking shark babies are, it’s not surprising that it takes a long time for them to develop in the womb. Embryos inside the eggs (inside the mother) develop for at least 3 years before the eggs hatch and the mother gives birth. And since it takes so long for the eggs to hatch, it makes sense that mom keeps the eggs safe in her own body instead of leaving them on the ocean floor!
A shark by any other name
Basking sharks were deemed “basking” because when they feed, it looks like they are basking in the sunlight. It doesn’t seem creative, but Britons alone have several names for the shark, in English, Irish, and even Orkney. Here are four other names for the basking shark (translated to English), and one made up. Which one do you think is fake?
- Elephant shark
- Bone shark
- Rib Mouth Shark
- Sun Shark
How endangered is this animal?
- The International Union for Conservation of Nature (IUOC) classifies the basking shark as an endangered species.
- Humans have hunted the species for centuries for its fins, meat, and livers. Many countries have had to pass legislation banning basking shark hunting or regulating it. Constant hunting plus a slow reproductive rate mean the population needs a long time to recover.
- Squelene is a popular ingredient in cosmetics because of its spreadability and anti-aging properties. Millions of sharks are killed every year for the squelene in their livers, which is put into makeup.
Twenty-Six-Foot-Long Basking Shark Washes Up on Maine Beach | Smart News | Smithsonian Magazine
Basking shark (Cetorhinus maximus) | Natural History Museum (nhm.ac.uk)
What would happen if a diver swam into the mouth of a basking shark? - Quora
Interview with Charles Hood, Filmer of Basking Sharks (redbull.com)
Basking Shark - Shark Facts and Information (sharks-world.com)
Cetorhinus maximus – Discover Fishes (ufl.edu)
Microplastics: what they are and how you can reduce them | Natural History Museum (nhm.ac.uk)
The Deadly Truth About Squalene & Squalane – Axiology (axiologybeauty.com)
Also Known As
Bone shark, Elephant shark, and Sun-fish
7–8.5 m (23–28 ft) in length with some individuals reaching 9–11 m (30–36 ft)
Worldwide in warm to cold temperate latitudes
Coast to the edge of the continental shelf
Plankton, fish eggs and fish larvae
About 50 years