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Sharks Porbeagle
Shark
Porbeagle Shark
Common Name: Porbeagle Shark
Scientific Name: Lamna nasus
Description
The Porbeagle
was first validly described as Squalus nasus by Bonnaterre
in 1788. Gunnerus had described it earlier in 1768
as Squalus glaucus, but this name was already in use for the
blue shark, now Prionace glauca. The current valid name of
this shark is Lamna nasus. The genus name Lamna is
translated from Greek "lamna, -es" as a voracious fish while
the species name nasus originates from Latin, meaning nose.
Habitat
Although
the Porbeagle is predominantly pelagic (open-ocean),
it can be found in both coastal and oceanic waters. The species
occurs in both hemispheres and is found at water temperatures
from 34o to 64oF (1o-18oC). It prefers cold water, but was
once recorded in water of 73oF (23oC). It does not appear
to enter freshwater, but has been caught in a brackish estuary
of Argentina. It can be found at the surface to a
depth of 2,346 ft (715 m).
Biology
The Porbeagle
has a heavy spindle-shaped body with a moderately long conical
snout. The gill slits are large. The caudal peduncle is strongly
keeled, with short secondary keels on the caudal base. The
caudal fin is crescent-shaped. The large first dorsal fin
has a white free rear tip. The second dorsal and anal fins
can pivot.The dorsal and lateral surfaces of the porbeagle
are dark blue to gray in color. The first dorsal fin is dark
with an abruptly white or gray free rear tip. The porbeagle
has a maximum total length of about 12 ft (365 cm) and maximum
weight of over 500 lbs (230 kg). Maximum age is likely about
30 years. There is considerable variation in estimates for
size at maturity for this species.
Food
Porbeagles
are opportunistic feeders. In the northwest Atlantic, their
diet consists primarily (90%) of teleosts (bony fish). In
the spring, these are mostly pelagic fish, like lancetfish,
herring, sauries, and mackerels. In the fall, these are mostly
groundfish, like sand lances, lumpsuckers, flounders, hakes,
and cod. Cephalopods, like squid, are the second most common
prey item.
Reproduction
In
the Northern Hemisphere, porbeagles mate autumn-winter
and give birth spring-summer. The little data that exists
for the Southern Hemisphere populations indicates
that they may be out of phase with those of the Northern Hemisphere,
giving birth off New Zealand and Australia in winter.
During mating, the male shark bites the female shark to hold
onto her while they copulate.Gestation is probably
eight to nine months. Litters of 1-6 embryos have been recorded,
but the usual number is 4, with 2 embryos per uterus. The
porbeagle is ovoviviparous, meaning that it gives
birth to live young, but in the uterus (womb), embryos have
no placental or other direct connection to the mother.
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