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Sunday, 27 April 2014 02:25

Grey Nurse Sharks - Diet & Life History

Diet

The diet of the adult Grey Nurse Shark consists of a wide range of fish, other sharks and rays, squids, crabs and lobsters. In Australia it is likely that the Grey Nurse Shark diet consists of species such as pilchards, jewfish, tailor, bonito, moray eels, wrasses, sea mullet, flatheads, yellowtail kingfish, small sharks, squid and crustaceans. Observations also suggest that schools of Grey Nurse Sharks can feed cooperatively by concentrating schooling prey before feeding on them. It is important to note that many of the species that comprise the Grey Nurse Sharks diet are also harvested by commercial, recreational and spearfishing interests, which is one of the main reasons that a number of commercial fisherman are not too friendly to grey nurse they happen to catch.

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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