If you saw a 15-foot-long shark swimming toward you with its mouth wide open, your life would probably flash before your eyes. This is precisely what happened to UK snorkeller Lew Smart in 2014.
Seeing a fin in the water, Smart jumped in to get a closer look and almost ended up in the mouth of this underwater giant.
Fortunately for Smart, basking sharks are non-aggressive sharks that filter-feed rather than attack.
They might have more teeth than any other shark but don’t appear to use them when eating.
As the second-largest fish in the sea, basking sharks have fascinated scientists and researchers since they were first discovered in 1765.
Despite that fascination, they haven’t managed to acquire a lot of knowledge about these mysterious creatures over the past 150 years. Those facts they have unearthed, we plan to share with you right here.
Key Takeaways From This Article:
Basking sharks are filter-feeders, not attackers.
Basking sharks are large with open mouths, making them easily recognizable.
Basking sharks are endangered due to human activities and reduced prey.
What do Basking Sharks Look Like?
The basking shark is one of the easiest ocean inhabitants to identify. It is huge, at between 22 to 29 feet long, and it also swims with its large mouth wide open.
When close to the surface, the basking shark’s large dorsal fin sticks out of the water along with its nose and the tip of its tail.
Each basking shark’s dorsal fin is unique, enabling scientists to identify individuals based on the notches and grooves visible on the fin. The dorsal fin may flop to one side in some large adults, making them even more discernible.
The basking shark’s appearance changes as it matures. At birth, the basking shark has a “long hook-like snout” which is thought to assist the young shark “by increasing water flow through the mouth.”
- Basking sharks are the second-largest living fish, after whale sharks. They can grow up to 10-12 meters (33-39 feet) in length, and weigh up to 5,200 kg (11,500 lbs).
- They are filter feeders, and mostly eat zooplankton such as copepods. They can filter up to 2,000 tons of water per hour while feeding.
- Basking sharks are found in all the world’s oceans, but they tend to prefer temperate latitudes and cold waters. They are most commonly spotted off the coasts of Europe and North America.
- They are sometimes known as the “sunfish” or “sailfish” because they often swim slowly at the surface with their dorsal fin exposed, as if basking in the sun.
- Despite their size, basking sharks are harmless to humans because they are not aggressive and feed only on small marine animals. However, they can accidentally bump boats while feeding or swimming.
- Basking sharks are classified as “vulnerable” on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, due to overfishing and accidental capture in fishing gear. Their populations have declined significantly over the past few decades.
During its first year of life, the basking shark’s snout straightens and lengthens rapidly, soon taking on the distinctive conical appearance of the adult.
Basking sharks are dark grey on their backs, with a pale underside common to many shark species. They have enormous mouths that can measure over three feet wide inside, which you’ll find more teeth than inside any other species of shark, numbering more than 1,500 at any one time.
Unlike predatory sharks, the basking shark doesn’t use its teeth for hunting; its preferred prey is roughly the size of a dime.
As far as scientists can figure out, the basking shark’s teeth are used only when mating, “allowing the shark pair to hold onto each other while internal fertilization is completed.”
Basking Sharks Taxonomy
Like all sharks, the basking shark is a cartilaginous fish and, as such, belongs to the Chondrichthyes class. These creatures have been around for some 450 million years but were first described in 1765.
At that time, they were assigned the scientific name Squalus Maximus. This genus has since been restricted to various types of dogfish, and the basking shark is now known as the Cetorhinus maximus.
The word Cetorhinus comes from the Greek words “kenos” and “rhinos”. Ketos refers to a marine monster or whale, while rhinos means nose. In other words, the basking shark is a large marine monster with a big nose!
Although the basking shark appears to have much in common with the whale shark, including size and diet, the two species are not closely related. Indeed, “they are further apart on the evolutionary tree than cats and dogs.”
Belonging to the Lamniformes order, also known as mackerel sharks, the basking shark is more closely related to the great white than the whale shark. Having said that, the basking shark is also the only remaining member of the family, Cetorhinidae.
Basking Shark Characteristics
The basking shark bears little resemblance to other mackerel sharks, many of which are fast-moving, predatory creatures. The basking shark ambles its way through the oceans, rarely exceeding 3.7kph.
Most of the time, the basking shark swims with its mouth open, filtering its microscopic prey out of the water as it moves.
Although most basking sharks measure less than 30 feet in length, the biggest one on record exceeded 40 feet!
The average basking shark weighs around 10,200 lb, but larger specimens could exceed 45,000 lb.
One of the most distinctive features of the basking shark is its enormous mouth, which it uses to consume millions of plankton every day. Scientists estimate that the basking shark filters somewhere in the region of “two million liters of water per hour through its gills.”
Although frequently seen near the surface, basking sharks can descend to depths of around 2,990 ft.
One of the most distinguishing characteristics of the basking shark is the large gill slits that almost entirely encircle the head. When the basking shark opens its mouth, the cartilage between each slit becomes visible. This cartilage is bright white and visible from the surface.
In addition to gill slits, basking sharks also have structures known as gill rakers, which it uses to catch plankton as the water filters through the mouth and gills.
Basking Shark Life Cycle
The basking shark’s life cycle remains something of a mystery, although scientists estimate that they live for around 50 years. This is a comparatively short lifespan compared to other species, like the great white, which lives to around 70, and the Greenland shark, which can live for hundreds of years.
Like many other shark species, the basking shark is thought to be ovoviviparous. The pups hatch from eggs inside the female’s body and continue to grow there, living off the egg’s yolk.
The gestation period of the basking shark lasts between two and three years, after which they give birth to a handful of large pups. These pups are born free-swimming and autonomous and have no further interactions with their parents.
Both male and female basking sharks are polyandrous and therefore have multiple mates.
For many years, scientists have wondered how these solitary giants find a mate in the ocean’s huge expanse, and a recent study appears to have found the answer.
Marine biologists in Ireland observed groups of six to 23 basking sharks swimming slowly in circles. The circle formations comprised equal numbers of male and female sharks, all gathering together in a kind of “slow motion ‘speed-dating’ event.”
It takes over a decade for a female basking shark to reach sexual maturity, although the exact age is widely contested. According to one source, they are sexually mature “after about 11.5 years,” while another claims it takes between “16 and 20” years.
Where do Basking Sharks Live?
Basking sharks have a global distribution. They frequent cold to temperate waters throughout the Atlantic and Pacific Oceans, the Mediterranean Sea, and the Sea of Japan. They are highly migratory, appearing to spend the spring and summer months closer to shore and the winters beyond the continental shelf.
The movements of the basking shark correspond to the availability of their main prey, although some scientists believe it’s “a type of hibernation.”
During the spring and summer, basking sharks appear to feed at the surface. At this time, they often come close to the surf zone and even enter the brackish waters of coastal lagoons and estuaries.
In the winter, their behavior and habitat change. The basking sharks move deeper into open water, leaving the coastline behind, as they seek out the “deep water over the upper continental slope and oceanic banks.”
According to a study conducted in the UK in 2003, basking sharks dive much deeper than other plankton-eating sharks. In accessing these deeper waters, they can exploit “zooplankton communities in mesopelagic (200 to 1000 m) as well as epipelagic habitat (0 to 200 m).”
Although primarily solitary, basking sharks are sometimes seen in large groups numbering 100s of individuals. This is presumably linked to their “speed-dating” method of finding a mate as it occurs in spring and summer, close to shore.
Basking Shark Behavior
One of the strangest behaviors exhibited by the basking shark is breaching. While fast-moving sharks often breach at the end of a high-speed hunt, basking sharks breach even faster, exceeding the top speed of the great white.
A 2018 study of basking sharks found that they “breached at approximately 5 meters per second,” marginally faster than the great whites “which clock in at 4.8 meters per second.”
Quite why this usually sluggish creature decides to suddenly propel its huge bulk out of the water at high speed remains something of a mystery.
Some scientists theorize that it could be a type of “male-male competitive behavior,” while others believe it’s intended to remove irritating parasites from the shark’s skin.
Basking sharks are non-aggressive creatures that tend to avoid boats and humans, although their sheer size makes them potentially dangerous.
One incident occurred in 1937 when a basking shark capsized a boat off the Kintyre Peninsula in Ireland. It’s believed a breaching basking shark landed on the vessel, snapping the main halliard and causing it to overturn.
There have also been reports of injured basking sharks attacking boats after being harpooned.
What do Basking Sharks Eat?
Despite being the second largest fish in the sea, the basking shark eats some of the ocean’s smallest inhabitants. Their diet consists of small copepods and other zooplankton, larvae, fish eggs, barnacles, and oceanic shrimp.
As they swim, basking sharks filter over 2.5 million liters of water every hour, extracting millions of tiny organisms with their comb-like gill rakers as they go.
The basking shark’s “olfactory tract is larger than the rest of its brain,” suggesting that they use a sense of smell to locate its prey.
Research indicates that basking sharks are incredibly adept at hunting out plankton, choosing areas with “specific zooplankton characteristics” that suit their tastes.
Researchers found that basking sharks feed predominantly on calanoid copepods, avoiding other smaller zooplankton species. They also migrate both horizontally and vertically in response to prey availability.
Not only do basking sharks seek out areas where their prey is most abundant, but they also target the most energy-rich sources.
What Hunts Basking Sharks?
The basking shark is so large that it doesn’t have many naturally occurring predators. A great white shark could potentially take down a basking shark, but there’s no evidence of such an attack ever occurring.
The most likely predator of the basking shark is the orca. Orcas, or killer whales, are quickly establishing themselves as the ocean’s top predator, taking on everything from the great white to the vast blue whale.
Earlier this year, footage emerged of killer whales attacking a juvenile whale shark off the coast of Panama. According to witnesses, the shark didn’t survive the incident.
If orcas are successfully preying on whale sharks, there’s nothing to stop them from taking on a basking shark, although the basking shark’s preference for colder waters could prove to be its saving grace.
The only other predator the basking shark has to fear is the human. Although the commercial fishing industry rarely targets basking sharks, some countries still hunt them for their fins and liver oil.
The basking shark is classified as an endangered species by the International Union for Conservation of Nature (IUCN) and currently faces the following threats:
- Entanglement in commercial fishing nets
- Collision with vessels
- Harassment from marine-based activities
- Reduced prey availability
Conclusion
The basking shark is a gentle giant enjoying nothing more than lazing around at the ocean’s surface, consuming huge mouthfuls of water and plankton.
Despite being generally solitary and slow-moving, the basking shark goes into overdrive when it’s time to find a mate.
Suddenly hundreds of basking sharks congregate for a speed-dating event that sees males leaping from the water at speeds faster than those achieved by the powerful great white.
The basking shark is one of just three plankton-eating shark species, the others being the whale shark and the megamouth.
It’s not particularly closely related to either one, however, having more in common with the great white!
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Hi, my name is Alex and I love Sharks and everything that lives in the sea 🙂