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Sharks Megamouth
Shark
Megamouth Shark
Common Name: Megamouth Shark
Scientific Name: Megachasma pelagios
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.
Range & Habitat
Range:
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.
Habitat:
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.
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