When you think of a shark, you might imagine a fearsome predator tearing through the water with rows of razor-sharp teeth. But the ocean is full of surprises, and the basking shark (Cetorhinus maximus) is one of the biggest. As the second-largest fish in the sea, this gentle giant reaches lengths of up to 40 feet and weighs more than a school bus, yet it poses absolutely zero threat to humans.
Instead of hunting seals or fish, the basking shark spends its days cruising the surface with its massive mouth wide open, filtering microscopic plankton from the water. Its name comes from this very behavior—it often looks like it’s simply “basking” in the sun, soaking up the warmth.
But don’t let the relaxed appearance fool you; these sharks are hard at work, filtering thousands of tons of seawater every hour to fuel their massive bodies.This guide dives deep into the fascinating world of the basking shark. From their colossal size and unique biology to their critical role in the marine ecosystem, we’ll explore why this endangered species is one of the ocean’s most misunderstood—and magnificent—inhabitants.
What Are Basking Sharks? Quick Facts
The basking shark is a creature of contradictions: massive but gentle, toothy but not biting, and widely distributed yet rarely seen. Taxonomically, it is the only living member of the family Cetorhinidae, making it a unique evolutionary branch in the shark family tree.
Scientific Classification:
- Scientific Name: Cetorhinus maximus (meaning “great whale-nosed shark”)
- Common Names: Basking shark, bone shark, elephant shark, sailfish
- Family: Cetorhinidae
- Order: Lamniformes (mackerel sharks)
- Class: Chondrichthyes (cartilaginous fish)
Key Characteristics:
- Size: 23-40 feet long (7-12 meters)
- Weight: 8,500-36,000 pounds (4,000-16,000 kg)
- Diet: Exclusively zooplankton (filter feeder)
- Lifespan: Estimated 50+ years
- Conservation Status: Endangered (IUCN Red List)
- Range: Temperate oceans worldwide
- Distinctive Feature: Massive gill slits that almost encircle the head
The scientific name Cetorhinus maximus is a perfect descriptor. It combines the Greek words ketos (whale) and rhinos (nose) with the Latin maximus (greatest). Essentially, it is the “greatest whale-nosed shark,” a fitting title for a fish that rivals whales in size and feeding habits.
How Big Do Basking Sharks Get? Size & Comparison
One of the most common questions people ask is: Just how big is a basking shark? The answer places them firmly in the realm of marine megafauna. While they don’t quite reach the colossal lengths of the whale shark, they dwarf almost everything else in the ocean.
Average vs Maximum Size
Typical Adult Measurements:
- Average Length: 26 feet (7.9 meters)
- Average Weight: 9,300 pounds (4,200 kg)
Maximum Recorded:
- Largest Documented: 40.3 feet (12.27 meters)
- Maximum Weight: Estimated 36,000 pounds (16,000 kg)
The largest confirmed specimen was a 40.3-foot giant caught in Canada’s Bay of Fundy in 1851. While 19th-century reports often exaggerated sizes, claiming sightings of 45-foot sharks, modern marine biologists rarely encounter individuals exceeding 33 feet.
Basking Shark Size Comparison
To truly appreciate their scale, it helps to compare them to other well-known species:
| Species | Average Length | Maximum Length | Average Weight |
| Basking Shark | 26 ft (7.9 m) | 40 ft (12.3 m) | 9,300 lbs |
| Whale Shark | 40 ft (12 m) | 60+ ft (18+ m) | 20,000 lbs |
| Great White Shark | 15 ft (4.6 m) | 20 ft (6 m) | 2,000 lbs |
| Human | 6 ft (1.8 m) | — | 180 lbs |
As the table shows, a basking shark is roughly double the length of a Great White and nearly five times heavier. Despite this intimidation factor, swimmers have nothing to fear—unless you happen to be a microscopic copepod.
Physical Characteristics & Identification
If you spot a large fin slicing through the water, how do you know it’s a basking shark and not a predatory species? Look for these unmistakable physical traits.
Distinctive Features
- Enormous Gill Slits
This is the most defining feature. The basking shark possesses five massive gill openings that extend almost completely around the head, looking like a collar. These slits can measure up to 3 feet long and are crucial for their survival, allowing for maximum water flow during filter feeding. - Huge Gaping Mouth
When feeding, the shark’s mouth opens to a cavernous 3 feet wide. It looks terrifying, but the throat is surprisingly narrow—so narrow that the shark couldn’t swallow a person even if it wanted to. - Prominent Dorsal Fin
The dorsal fin is tall and triangular, often reaching over 3 feet in height. Unlike the stiff, upright fin of a Great White, a basking shark’s fin can sometimes flop to the side when it’s at the surface. - Conical Pointed Snout
While many large sharks have broad, flat heads, the basking shark has a distinctly conical, pointed snout. This shape helps streamline its massive bulk as it moves through the water.
Basking Shark Teeth Structure
Here is one of the most surprising basking shark facts: they have teeth, but they don’t use them.
Teeth Characteristics:
- Size: Tiny, only 5-6mm (0.2 inches)—about the size of a grain of rice.
- Number: Hundreds arranged in multiple rows (100+ per row).
- Shape: Conical and curved backward (hooked).
- Function: Essentially non-functional for feeding.
In contrast to the 2.5-inch serrated teeth of a Great White, the basking shark’s teeth are evolutionary leftovers. They play no role in catching food.
Gill Rakers: The Real Filtering System
Since teeth are useless for catching plankton, the basking shark relies on gill rakers. These are dark, bristle-like projections that line each gill arch. They act like a biological sieve. As water rushes into the mouth and out through the gills, the rakers trap tiny organisms in a fine mesh, allowing the shark to swallow the concentrated food while the water exits.
Coloration & Skin
Basking sharks are typically dark gray-brown to nearly black on top (dorsal side), fading to a paler gray or dull white underneath (ventral side). Their skin is incredibly rough, covered in tiny, tooth-like scales called dermal denticles. This “sandpaper” skin is coated in thick mucus. While the shark is gentle, brushes against its skin can cause severe abrasions to divers.
What Do Basking Sharks Eat? Diet & Feeding
Basking sharks are obligate planktivores, meaning they are biologically committed to a diet of microscopic organisms.
Diet Composition
Primary Food Sources:
- Copepods: These tiny crustaceans (1-5mm) make up the bulk of the diet.
- Barnacle & Decapod Larvae: Seasonal treats including crab, lobster, and shrimp larvae.
- Fish Eggs: Consumed during spawning events.
- Krill and small shrimp.
Important Note: Unlike some filter feeders, basking sharks do not eat phytoplankton (plant plankton). They focus exclusively on zooplankton (animal plankton) to get the necessary protein and fat.
Filter Feeding Mechanism Explained
The feeding process is a marvel of biological engineering. Unlike whale sharks, which can suck water in, basking sharks rely on forward motion to feed.
How It Works:
- Mouth Opens: The shark opens its mouth ~3 feet wide while swimming at a steady 2-3 mph.
- Water Intake: Water flows passively into the mouth and across the gills at a rate of up to 2,000 tons per hour.
- Filtration: The gill rakers catch the plankton while the water passes out through the gill slits.
- Swallowing: roughly every minute, the shark closes its mouth to swallow the accumulated prey.
Daily Consumption
To maintain a body weight of over 10,000 pounds, a basking shark must consume approximately 2,000 pounds (900 kg) of plankton every single day. Achieving this requires filtering roughly 4 million pounds of water during extended feeding sessions.
Feeding Behavior Patterns
Surface Feeding:
This is the behavior that gave the shark its name. When plankton blooms near the surface due to sunlight and warmer temperatures, the sharks cruise slowly with mouths agape.
Group Feeding:
While often solitary, basking sharks are social when the food is good. They have been known to aggregate in groups of 50 to 100 individuals when they encounter dense plankton patches.
Deep Water Feeding:
Recent tracking data has busted the myth that these sharks hibernate in winter. Instead, they often follow plankton migrations into deep water, feeding at depths exceeding 3,000 feet where food sources are still available.
Where Do Basking Sharks Live? Habitat & Distribution
You can find basking sharks in temperate and boreal oceans all around the globe. They prefer cool to temperate waters, generally avoiding the warm tropics.
Global Distribution
Northern Atlantic:
- United Kingdom and Ireland (especially the Hebrides in Scotland)
- North Sea, Norwegian Sea, and Iceland
- Canada (Newfoundland, Bay of Fundy)
- U.S. East Coast (New England)
Northern Pacific:
- Alaska and British Columbia
- U.S. West Coast (specifically Monterey Bay, California)
- Japan and Korea
Southern Oceans:
- South Africa
- Southern Australia and Tasmania
- New Zealand
- Chile and Argentina
Preferred Habitat
Basking sharks prefer water temperatures between 46-58°F (8-14°C), though they can tolerate a range from freezing up to 75°F. Their habitat use changes based on the location of their prey. They are surface dwellers during plankton blooms but become deep-sea travelers during transit, occupying depths from 100 to 3,000+ feet.
Seasonal Migration
Spring/Summer (April-August):
This is the best time to spot them. They move into shallow coastal waters to feast on seasonal plankton blooms. Hotspots include Cornwall (UK), Ireland, and the Canadian Maritimes.
Autumn/Winter (September-March):
For years, scientists thought basking sharks hibernated on the seafloor because they disappeared from the surface. We now know they migrate. Some dive deep to chase zooplankton, while others undertake massive journeys. Tagged individuals have been tracked traveling 6,000 miles from the British Isles to Newfoundland, proving they are capable navigators rivaling the Great White.
How Long Do Basking Sharks Live? Lifespan & Reproduction
Lifespan
Estimating the age of a shark is difficult because their skeletons are made of cartilage, which doesn’t hold growth rings as well as bone. However, scientists estimate the basking shark lifespan to be 50+ years. Some research suggests they may live as long as 70 years.
Reproduction
The basking shark’s life cycle is slow, which is a major factor in their endangered status.
- Sexual Maturity: Males don’t mature until they are 13-16 feet long (6-13 years old). Females take even longer, maturing at 16-20 feet long (12-20 years old).
- Reproductive Strategy: They are ovoviviparous. This means the eggs hatch inside the mother’s body, and the pups are born live.
- Gestation Period: A staggering 2-3.5 years. This competes with the elephant for the title of longest pregnancy in the animal kingdom.
- Litter Size: Relatively small, estimated at 2-4 pups per pregnancy.
- Pup Size: Pups are born large and independent, measuring 5-6 feet (1.5-1.8 meters).
Because females likely only reproduce every 2-4 years, a single female may only produce 10-20 offspring in her entire life. This extremely low reproductive rate makes the species highly vulnerable to population crashes.
Conservation Status & Threats
Are Basking Sharks Endangered?
Yes. The IUCN Red List classifies the basking shark as Endangered. Global populations are estimated to have dropped by 80% between the 1950s and the 2000s.
Main Threats
- Historical Commercial Hunting
For decades, basking sharks were targeted for their massive livers. A single shark’s liver can account for 25% of its body weight and yield up to 500 gallons of oil. This oil was used for lamps, lubricants, and cosmetics. While large-scale hunting has largely stopped, the populations have never fully recovered. - Bycatch
Even though they are no longer hunted, they often get tangled in fishing nets and longlines meant for other species. - Boat Strikes
Because they spend so much time slowly swimming at the surface, basking sharks are prone to collisions with vessels. - Climate Change
Rising ocean temperatures and ocean acidification can alter the distribution and abundance of plankton. If the food moves or dies off, the sharks starve. - Microplastics
As filter feeders, basking sharks ingest whatever is in the water column, including microplastics and chemical pollutants that can harm their health.
Protection Measures
Fortunately, conservation efforts are ramping up. The species is now protected in the UK, US, Canada, New Zealand, and EU waters. International trade is restricted under CITES Appendix II. Additionally, research programs and citizen science databases are helping scientists understand migration patterns to better protect critical habitats.
Frequently Asked Questions
1. Are basking sharks dangerous to humans?
No. Basking sharks are gentle giants. They eat microscopic plankton and have no interest in humans. There has never been a recorded attack on a human. However, divers should keep a respectful distance; their skin is like coarse sandpaper and can cause injury if brushed against, and their sheer size makes accidental impact dangerous.
2. How big do basking sharks get compared to whale sharks?
Basking sharks are smaller than whale sharks. A basking shark averages 26 feet, while a whale shark averages 40 feet. In terms of weight, a whale shark is more than double the weight of a basking shark.
3. What is the scientific name for basking sharks?
The scientific name is Cetorhinus maximus. It translates roughly to “greatest whale-nosed shark,” referring to its massive size and whale-like feeding habits.
4. Where can I see basking sharks in the wild?
The best places to see them are in temperate coastal waters during plankton blooms (May-August). Top locations include the Inner Hebrides in Scotland, the west coast of Ireland, Cornwall in England, and the Bay of Fundy in Canada.
5. Do basking sharks have teeth?
Yes, but they are tiny (about 0.2 inches) and non-functional. They have hundreds of these hooked teeth, but they rely entirely on their gill rakers to filter food.
6. How long do basking sharks live?
They are estimated to live 50 years or more. Their slow growth and late maturity suggest a long lifespan, similar to other large shark species.
7. What do basking sharks eat besides plankton?
Nothing. They are strict planktivores. Their throat structure prevents them from swallowing anything larger than small invertebrates.
8. Why are they called “basking” sharks?
They are named for their habit of swimming slowly at the very surface of the water, which makes them look like they are sunbathing or “basking” in the warmth of the sun.
9. How do basking sharks reproduce?
They are ovoviviparous (eggs hatch inside the mother). The gestation period is incredibly long—up to 3.5 years—and they give birth to live, fully formed pups.
10. Can you swim with basking sharks?
In many parts of the world, yes. It is a popular eco-tourism activity in the UK and Ireland. However, strict codes of conduct usually apply, requiring swimmers to maintain a distance of at least 10 feet to avoid disturbing the animal.
Conclusion
The basking shark (Cetorhinus maximus) is a testament to the diversity and wonder of our oceans. It challenges our perception of sharks, proving that the biggest inhabitants of the deep are often the most gentle. From their complex filter-feeding mechanisms to their epic trans-Atlantic migrations, these animals are marvels of evolution.
However, their story is also a cautionary one. Their slow reproductive rates and history of exploitation have left them in a precarious position. By understanding the facts—their size, biology, and behavior—we can better advocate for their protection. Whether you are lucky enough to spot a dorsal fin breaking the surface off the coast of Scotland or simply admiring them from afar, the basking shark commands respect as one of the ocean’s true giants.