The megamouth shark is a rare shark and a large species, reaching weights of 2700 pounds (1215 kg). However, it is the smallest of the three species of filter-feeding sharks, behind the whale shark and the basking shark. The megamouth shark gets its name from the remarkably large, circular mouth.
The megamouth has a brownish-blackish color on top and white underneath, a broadly rounded snout, and a distinctive large head with rubbery lips. They can grow to 18 feet in length. The capture in a drift net of a megamouth shark in California in 1990 was very important in understanding the species. The megamouth shark was tagged and released and followed for two days. Its pattern of behavior, staying at a depth of 50 feet during the night, then diving to 500 feet at dawn, would indicate it is a vertical migratory over a 24-hour span.
The unique appearance of the megamouth
The megamouth is known for its largemouth that it uses to filter plankton from the water. “It is also believed that its lips are bioluminescent, which attracts prey to it in the deep sea where it normally lives,” Colin explained.
Because the mouth and jaw are much larger than the shark’s abdomen, the megamouth doesn’t have the strongest swimming abilities.
Distribution And Habitat
Its distribution and habitat are still uncertain, but a few sightings in areas of the Pacific, Indian, and Atlantic Oceans are on record; and since its discovery in Hawaii, only 55 more sightings have been registered in countries such as Brazil, Senegal, the Philippines, and Indonesia. The first discoveries were on the coasts of California, Japan, and Australia, in addition to the Hawaiian islands.
It is an inhabitant of the deep waters (between 150 and 1,000 meters) that like moderate and warm temperatures.
Feeding
Instead of swimming continuously with its enormous mouth wide open, filtering water for plankton and jellyfish, it is thought to attract prey with a bioluminescent strip along its upper jaw and then engulf prey in a single motion, similar to the feeding mechanism of a whale. This is thought to be due to the restricted internal gill openings and jaw morphology of the megamouth shark. It is thought that swimming with its mouth open would push water and prey aside, as the water will not be able to pass at any great rate between the densely packed papillose gill rakers and through the relatively small internal gill rakers.
Evidence of a Megamouth spotted
Scientists put radio tags on a male Megamouth that was caught in a net in 1990 and tracked it for two days, revealing that the sharks undergo vertical migration. Tom Haight, who swam with the shark and photographed it underwater as the animal was tagged and released, wrote that “From dawn to sunset, he swam slowly at 450 to 500 feet into the prevailing current, apparently feeding on krill that were at that depth during the daytime. From sunset to sunrise he ascended to 39 to 46 feet below the surface to feed on the krill as they also ascended. The extreme daylight depth could explain why the megamouth shark is so rarely spotted.”
Breeding
Megamouth sharks mate via internal fertilization and give live birth to a small number of relatively large young. Though they give live birth, these sharks do not connect to their young through a placenta. Instead, during the gestation period, the mother likely provides her young with unfertilized eggs that they actively eat for nourishment. After they are born, young megamouth sharks immediately become filter feeders. The megamouth shark is not targeted by commercial fishers, but it is often sold when captured accidentally in fisheries targeting other species.
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