Megamouth Shark

Megamouth Shark : Description

When the first megamouth shark was captured in 1976, a new shark family, genus and species had to be erected. There are conflicting phylogenetic hypotheses regarding the evolutionary relationships between the Megachasmidae and other shark families. One theory suggests that the Megachasmidae is evolutionary derived and form a monophyletic family with basking shark, Cetorhinidae. Recent studies suggest that Megachasma pelagios is the most primitive living species within the order Lamniformes. The currently valid genus Megachasma is derived from the Greek "megas, megalos" = great and "chasma" = cave, while the species name pelagios is also Greek, meaning of the sea.

Megamouth Shark : Range & Habitat

Although only 37 confirmed sightings (See Table) of megamouth shark are reported, this species is now known from Indian, Pacific and Atlantic Oceans. As with the two other filter-feeding sharks, the basking and whale sharks, this species is wide-ranging.

As its species name (pelagios) suggests, the megamouth lives epipelagicly (in the upper part of the water column) in open ocean. It remains at a depth of 15m during the night, then dive to 150m at dawn and returned to shallow waters at dusk.The megamouth is presumed to be a vertical migrator on a diel cycle, spending the daytime in deep waters and ascending to midwater depths at night.

Biology

Megamouth, in contrast to many other deep-water sharks, shows a decrease in specific gravity in the form of a soft, and poorly calcified cartilaginous skeleton; very soft, loose skin; and loose connective tissue and muscles.The sizes of all reported megamouth sharks are listed in a table (See Table). Maximum size is at least 550cm (17ft). Males mature by 400cm (13ft) and female by 500cm (16ft). Dorsal surface of body, pectoral and pelvic fins, dorsal fins, center of anal fin and caudal fin are blackish brown. Ventral surface of body, below level of pectoral end pelvic fins, tips and posterior margins of pectoral and pelvic fins, abruptly white, as the posterior margins of dorsal and anal fins and postventral caudal margins.

Food

The megamouth shark, which reaches over than 500cm in length, is one of the three giant filter-feeding sharks in the sea. The other two are the basking shark and the whale shark. Precise details of feeding behavior are unknown due to the lack of observations on a live, feeding specimen.

Predators

The only confirmed register of a megamouth predator is an isolated event of sperm whales (Physeter macrocephalus) attacking this shark. This occurred in Manado, North Sulawesi, Indonesia (30th August 1998) near midday, while some researchers were observing the whales. The base of the dorsal fin and the gills of the shark showed signs of the whales' attack.