Megamouth Shark

What is megamouth shark?

The megamouth shark (Megachasma pelagios) is a rare species of large filter-feeding shark that inhabits tropical and temperate oceans worldwide. First discovered in 1976 near Hawaii, it is the only living member of the family Megachasmidae.¹²

These sharks are characterized by a bulky, teardrop-shaped body, a bulbous head, and an unusually wide mouth containing up to 50 rows of tiny teeth. They are slow swimmers that migrate vertically in the water column to follow plankton, though they may also consume small bony fishes and jellyfish. Females are significantly larger than males, reaching lengths of up to 7.1 meters (23.3 feet).³¹

While the International Union for Conservation of Nature and Natural Resources (IUCN) lists the megamouth shark as a species of least concern, it is incredibly rare and faces potential risks from commercial fishing bycatch.³¹

What are the other two filter-feeding shark species?

The three large filter-feeding sharks are the whale shark, the basking shark, and the megamouth shark.⁴

• Whale shark (Rhincodon typus): As the largest living fish, this species inhabits tropical oceans worldwide. It utilizes elaborate spongy tissue supported by its gill arches to strain plankton and small organisms from the water.⁵⁴
• Basking shark (Cetorhinus maximus): This massive, slow-swimming shark is found in temperate coastal regions. It feeds by swimming with its mouth open, using modified gill rakers to sift copepods and other zooplankton from the water.³⁴

These sharks are unique among their kind for their specialized feeding apparatus, which functions similarly to the baleen found in whales.⁴

How does filter feeding work in sharks?

Filter feeding in sharks is a specialized method of food procurement used by the three largest shark species: the whale shark, the basking shark, and the megamouth shark. Unlike predatory sharks that hunt individual prey, these species subsist on minute, drifting organisms known as plankton.⁸⁵⁶

To capture this food, these sharks utilize a straining apparatus analogous to the baleen found in whales. The mechanism functions as follows:⁵

• Water Intake: As the shark swims with its mouth open, seawater containing plankton and other small organisms enters the mouth cavity.⁸
• Straining: The water is filtered through the gill slits. The sharks are equipped with specialized structures that act as a sieve to trap prey while allowing water to pass through and return to the sea.⁸⁵
• Specialized Anatomy: The basking and megamouth sharks utilize modified gill rakers for this process, while the whale shark employs elaborate, meshlike spongy tissue supported by its gill arches.⁵⁶
• Consumption: Periodically, the shark closes its mouth to swallow the concentrated prey trapped by the straining apparatus.⁸

What is oophagy and why do some sharks practice it?

Oophagy is a form of cannibalism in which developing shark embryos consume unfertilized eggs or their own siblings within the mother’s uterus.¹⁰³

This behavior occurs in certain ovoviviparous shark species, such as the porbeagle, the mako, the sand shark, the megamouth shark, and the white shark.¹⁰³⁶

Sharks practice oophagy as a reproductive strategy to provide supplemental nourishment to the developing young after their initial yolk sacs are exhausted. By consuming these nutrient-rich resources, the embryos can grow significantly larger before birth. While this process typically results in a smaller number of offspring per litter, the young are born at a more advanced stage of development, which may enhance their chances of survival in the wild.¹⁰³