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How differentiate
the two sexes
To differentiate a male from a female you must look underneath the shark
at the pelvic fins. Males have claspers extending from the pelvic fins
(see diagram), females do not.
Little is known about the
reproductive biology of Grey Nurse Sharks in Australian waters.
Consequently, the timing of mating and pupping in Australia is unknown.
Reproductive
Biology
The Grey Nurse Shark has
a relatively low growth rate and take 4 - 6 years to mature, with both
males and females maturing at about 220cm total length. The precise
timing of mating and pupping in Australian waters is unknown. Many
sharks have been observed at Pimpernel Rock, NSW during the months of
March and April with mating scars, ie. bite marks around the pectoral
fins and head area. In South Africa mating occurs between late October
and the end of November, with pregnant females moving southwards each
year during July and August to give birth in early spring, then
returning northward. Once impregnated, the female stores the sperm while
the ovaries produce eggs that move to the oviduct where they are
fertilised. Not all-migrating females are sexually active and generally
only reproduce once every two years. Therefore, on average, mature
females produce only one pup each year.
The reproductive norm for
the Grey Nurse Shark includes oophagy and intra-uterine cannibalism
which results in a maximum of two young per litter (one in each uterus).
Embryos hatch into the uterus at about 55 mm long and at lengths of
around 10 cm they develop teeth and consume other embryos in the uterus.
The single remaining embryo in each uterus then feeds on any
unfertilised eggs as the female continues to ovulate. Gestation takes
9-12 months.
Young
At birth the Grey Nurse
Shark pups measure on average 1 metre in length. In Australia it appears
that these sharks give birth at select pupping grounds. In July 2001 the
first recorded birth of a Grey Nurse Shark was observed, one pup was
born in the late morning at Julian Rocks - Byron Bay.
Longevity
A Grey Nurse Shark held
in captivity at a Sydney aquarium lived for 13 years, and others have
lived for over 16 years in captivity in South Africa. The average life
span of this species in the wild is unknown, although it is likely that
larger specimens in the wild may be much older than 13 or 16 years.
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