The megamouth is the newest and most intriguing species of large shark to have been discovered in recent years.
The first one was caught by accident in 1976; since then, there have only been a handful of sightings.
The megamouth shark appears to be a rather solitary and elusive creature that occupies the ocean’s dark depths during the day, coming close to the surface only after night has fallen.
Although scientists are still accumulating data about this unusual shark, they have made some interesting discoveries about its habitat, behavior, and diet.
What do Megamouth Sharks Look Like?
It’s impossible to confuse the megamouth shark with any other creature. Its large mouth, rubbery lips, and bulbous head make it unmistakable, not that you’re likely to see one anytime soon.
Humans rarely get to see these elusive creatures, and when they do, they’re often already dead.
On an average-sized megamouth of 17 feet long, the mouth would measure approximately 4 feet across. No wonder scientists decided to call it the megamouth!
The megamouth’s cavernous mouth is full of teeth. Each jaw features around 50 rows of small teeth, although only three of these are functional.
The megamouth’s upper jaw is protrusible, meaning the shark can extend it forward. When it does this, it exposes a distinct white band between the snout and upper jaw.
Like most other sharks, the megamouth is lighter underneath than it is on its dorsal side.
This dual coloration camouflages the shark, protecting it against potential predators. The dorsal side of the megamouth shark is usually brown or grey, while the belly is creamy white.
The megamouth also has black spots under its lower jaw and white tips on its fins, or so we believe. Megamouth shark sightings are extremely rare, and all the information we have comes from just 117 specimens.
Megamouth Sharks Taxonomy
The megamouth shark was only discovered about 40 years ago, in 1976, when a U.S. Navy research vessel discovered an adult male off the coast of Hawaii.
The specimen was so different from every other shark species that scientists gave it a new genus and species.
The megamouth shark is in a league of its own, taxonomically speaking, and is the only remaining member of the only genus left in the family Megachasmidae.
Fossilized teeth suggest that two other species of megamouth once swam in our oceans, but there’s no sign of them now.
The megamouth’s scientific name, Megachasma pelagios, refers to its chasm-like mouth and the fact that it lives in the sea.
There has been some debate over the megamouth’s possible connection to the basking sharks, but it’s unclear if they descended from the same ancestral lineage or not.
Although it may not resemble the great white, the megamouth shark is loosely related to this notorious species. Both belong to the Lamniformes order, along with all other species of mackerel shark.
Megamouth Sharks’ Characteristics
Megamouth sharks are large and slow-moving. They average around 13 to 16 feet in length, with some individuals growing up to 17 feet long or possibly longer.
There are reports of a 23-foot-long carcass found off the coast of Taiwan, but I couldn’t find any evidence to support those claims.
Unlike the muscular great white, the megamouth shark is a rather flabby creature that ambles around the ocean at speeds of between 1.5 to 2.1 kph.–
The megamouth has “very flexible and mobile” pectoral fins that give it the stability it needs to swim at such slow speeds.
Despite their size, megamouths aren’t particularly robust sharks. They have poor muscle structure, soft fins, and “skeletons that are poorly calcified.”
At one stage, scientists thought that the megamouth might be capable of producing bioluminescence to attract its prey, but it’s unclear whether this is actually the case. It’s possible that the white band on the megamouth’s snout reflects light rather than produces it.
The megamouth shark is the third largest shark in our oceans. Like the whale shark and basking shark, it’s also a filter feeder, although it uses a slightly different method to the others.
Megamouth Sharks’ Life Cycle
Due to the megamouth’s elusive nature, we know hardly anything about its life cycle. It’s presumed to be ovoviviparous simply because most other sharks are, and we’re fairly sure reproduction takes place via internal fertilization.
As an ovoviviparous species, a female megamouth would lay and hatch eggs inside her uterus and nurture the embryos for several months before giving birth to live young.
We don’t even know how many megamouth shark pups there might be in a litter but judging by their scarcity, probably not very many.
Megamouth sharks are thought to measure less than 5’8” at birth and reach maturity at around 14 feet for males and 16’ for females.
The large size of the pups also supports the theory that the female megamouth only gives birth to small litters.
The lifespan of the megamouth shark is also unknown. Judging by what we know of other filter-feeding sharks, it’s probable that they live anywhere between 50 and 100 years.
Where do Megamouth Sharks Live?
Megamouth sharks are rare but have an almost global distribution. They can be found in temperate and tropical oceans worldwide, including the Atlantic, Indian, and Pacific.
Most megamouth sightings have taken place off the coast of Japan, the Philippines, and Taiwan, but they’ve also been seen close to the San Diego coastline in recent months.
A study of the genetic diversity of the megamouth population caught both close to Taiwan. In Baja California, Mexico concluded that the “low genetic diversity” was indicative of a small migratory population.
In addition to traveling across oceans, megamouths also move vertically. During the day, they descend to depths up to 15,000 feet, while at night they’ll feed close to the surface.
Studies suggest that megamouths move from around “39 to 46 feet below the surface” at night to “450 to 500 feet” during the day.
This type of movement is known as diel migration. It’s probable that, in doing this, the megamouth is mirroring the progress of its favorite food – krill. It would also explain why megamouth sightings are so incredibly rare.
Megamouth Shark Behavior
Like other filter-feeding sharks, megamouths are gentle and docile. They lack the aggressive of predatory sharks like the bull shark and great white because catching tiny prey doesn’t require it.
Thought to be a primarily solitary creature, the megamouth swims with its mouth open, sucking its prey in as it traverses the oceans.
It’s less active than other filter feeders and appears to be a comparatively poor swimmer. Its swimming speed is “less than half the average cruising speed recorded for large predatory sharks” and well below the optimal swimming speed for a fish of this size.
Nevertheless, it’s normal for sharks to move slowly in the cold, deep waters where megamouths are often found. The Greenland shark, for example, moves at just 0.3m per second, or just over 1 kph.
These deep-water sharks probably need to move slowly to conserve enough energy to maintain their body temperature in such frigid waters.
During the day, megamouth sharks remain at depth but well above the bottom of the ocean, averaging around 490 feet. At night, they follow their prey into the ocean’s upper layers, averaging depths of approximately 56 feet.
Research indicates that the megamouth’s more extreme depth changes occur at “the times of maximum rate of change in ambient light,” suggesting that they move in response to changes in light levels or to their prey’s reaction to light.
What do Megamouth Sharks Eat?
Although the megamouth’s diet is similar to that of other filter-feeders, it has a slightly different way of consuming it.
Employing “a kind of low-velocity, high-volume suction feeding” mechanism, the megamouth swims slowly through schools of plankton and krill with its jaws wide open. It then creates suction by protruding its jaws and lowering the pharynx and tongue.
By swimming into the current, the megamouth can effectively ram prey into its giant mouth.
Although some sources claim that the megamouth “feeds exclusively on euphausiids” or krill, others believe it likes a little variety in its diet. According to them, the megamouth will throw a few “copepods and gelatinous zooplankton” into the mix, given the opportunity.
Given their considerable size, megamouth sharks probably need to consume large quantities of food, although their slow swimming speed will help to offset their energy demands.
A juvenile whale shark measuring 19 feet long is thought to consume around “46 pounds of plankton per day,” suggesting that an adult megamouth would probably need between 30 and 40 pounds of food each day to survive.
What Hunts Megamouth Sharks?
Megamouth sharks may not be aggressive, but they are big, which deters most potential predators.
The only report of anything attacking a megamouth involved a trio of sperm whales. This incident occurred in 1998 in Manado, North Sulawesi, Indonesia, and was observed by a group of researchers.
After the attack, the megamouth had injuries to its dorsal fin and gills, but whether it survived or not remains a mystery.
This attack was a rare occurrence, although sperm whales have been known to attack other shark species in addition to the megamouth.
There’s also evidence to suggest that the megamouth sustains injuries from the cookie-cutter shark, but these are unlikely to be fatal.
The cookie cutter is a small shark that takes cookie-sized chunks out of its victim without endangering their lives.
Although the commercial fishing industry presents some risk to the megamouth shark in the form of bycatch, it’s not targeted as other shark species are.
Megamouths that are accidentally caught by fisheries targeting other species may be sold for meat.
A few years ago, a megamouth shark caught off the coast of eastern Taiwan was sold to a local seafood restaurant for nearly $2,000!
Fortunately, scientists took what samples they needed before the shark was sold, but the incident still left the environmental group Kuroshio Ocean Education Foundation calling for “a ban on catching megamouths.”
Our understanding of the megamouth’s life is still extremely limited, largely due to its preference for deep-water habitats during the day.
It differs from most other sharks in both appearance and behavior, lacking the aggression and speed of predatory sharks.
It’s most closely related to the basking shark, which displays similar behavioral traits and uses a similar feeding mechanism.
Although the megamouth shark could, theoretically, swallow a human whole, it appears to prefer microscopic organisms, like krill, and is generally gentle and non-aggressive around humans.
Hopefully, scientists will soon discover more about the megamouth’s life cycle, reproduction, and behavior, giving us a clearer insight into what role this species plays in our marine ecosystems.
For now, let’s simply celebrate that such a strange and unique creature exists.
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.